Acid-promoted cyclization of 2,4-diaryl-1,1,1-trifluorobut-3-en-2-oles and their TMS-ethers into CF₃-indenes

Abstract

2,4-Diaryl-1,1,1-trifluorobut-3-en-2-oles and their TMS-ethers in H₂SO₄ at room temperature in just 2 min are quantitatively cyclized into 1-aryl-3-trifluoromethyl-1H-indenes. The reaction proceeds through an intermediate formation of the corresponding CF₃-allyl cations, which are cyclized regioselectively at the allyl carbon atom most remote from the CF₃-group. The obtained CF₃-indenes in solution of EtOAc in the presence of silica gel at room temperature over 4 h are quantitatively isomerized into 3-aryl-1-trifluoromethyl-1H-indenes.

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Introduction

Allyl alcohols are valuable synthons in organic chemistry. Recently we have shown^1–3 that reactions of some trifluoromethyl substituted allyl alcohols with arenes under the action of Brønsted or Lewis acids have resulted in the formation of trifluoromethylated alkenes, indanes, or indenes. Synthesis of indenes^4–6 is an actual goal in chemistry, biology, and medicine. For instance, indene derivatives are widely used as biologically active compounds,^7,8 and ligands for metallo-complexes.^9–12 Introduction of a trifluoromethyl group into the indene core may confer new chemical, biological (lipophilicity and bioavailability), and physical properties to the molecules, due to the strong electron acceptor characteristic of the CF₃ group. CF₃-indenes are rather rare compounds, and there are just a few reports on their synthesis.^13–17 For instance, Langlois et al. showed just one example of BF₃-promoted cyclization of CF₃-allyl alcohol into the corresponding CF₃-indene.¹³

The main goal of this work was a study of acid-promoted electrophilic transformation of 2,4-diaryl-1,1,1-trifluorobut-3-en-2-oles 2 and their TMS-ethers 1. CF₃-TMS-ethers 1 are easily available from chalcones by trifluoromethylation of the carbonyl group with CF₃TMS followed by desilylation with SnCl₂ or aqueous HCl leading to CF₃-allyl alcohols 2 (Scheme 1).

Scheme 1 Synthesis of CF₃-TMS-ethers 1 and the corresponding CF₃-alcohols 2 from chalcones (see substituents R¹, R² in aryl rings Ar¹, Ar², respectively, in Table 1).

Results and discussion

First, we decided to study plausible reaction cationic intermediates by means of quantum chemical calculations. One would expect that compounds 1/2 under the action of Brønsted or Lewis acids could give rise to the corresponding CF₃-allyl cations.¹³ To estimate electronic characteristics of these cations we carried out DFT calculations of species A generated from 1a/2a by the protonation of the OX group (X = TMS or H), followed by elimination of HOX (Fig. 1). The following parameters were calculated: E – energy of the HOMO and LUMO, global electrophilicity index ω,^18,19 natural charges q, contribution of the atomic orbital to the molecular orbital k. The calculation shows that carbon C² bears a large negative charge −0.21e, but carbon C⁴ has a small positive charge and gives rather big contribution (19.6%) to the LUMO. These data demonstrate that the reactive electrophilic center of cation A should be carbon C⁴ by both charge and orbital control. Species A possesses a big value of ω index 7.0 eV, pointing out its high electrophilicity.

Fig. 1 Selected electronic characteristics (DFT calculations) of cation A generated from 1a/2a by protonation of the OX group, followed by elimination of HOX (energy of the HOMO and LUMO E, global electrophilicity index ω = (E_HOMO + E_LUMO)²/8(E_LUMO − E_HOMO), natural charges q, contribution of the atomic orbital to the molecular orbital k).

Then we carried out reactions of the series of compounds 1/2 under the action of various acidic reagents (Table 1). Indeed, the cyclization of 1/2 into CF₃-indenes 3 takes place showing that carbon C⁴ is a reactive center in the corresponding intermediate cations A. Among all other tested Brønsted and Lewis acids, sulfuric acid (H₂SO₄) was found to be one of the best for this transformation, and the reaction in this acid took just 2 min (Table 1). Alcohol 2a was not converted into acetic acid (room temperature, 4 h), and remained unreacted. On the other hand, strong Lewis acids AlX₃ (X = Cl, Br) in the reaction with 2a led to complex oligomeric mixtures. The same reaction in trifluoroacetic needed a longer time (room temperature, 1 h) and gave 3a in 88% yield. Triflic acid CF₃SO₃H (TfOH) may be used as well; indene 3a was formed in 2–3 min in 82% yield in this acid. However, we finally chose H₂SO₄ because it is a cheap and easy to handle reagent.

Table 1 Cyclization of compounds 1/2 in H₂SO₄ (50 equiv.) at room temperature for 2 min leading to CF₃-indenes 3

Entry	Starting compounds			Reaction products
	1/2	R^1, R^2 in 1/2, R^2 in 3		R^1	3 ^a (yield, %)
		R^1	R^2
a Isolated yields. b Yield obtained with the reaction in CF3CO2H (50 equiv.), instead of H2SO4, for 5 min. c Two regioisomers 3j1 and 3j2 with a ratio 1.25 : 1 and 96% yield were obtained. d The mixture of isomeric indenes 3q and 4q in a ratio of 8 : 1, respectively, was obtained (see Scheme 2).
1	1a/2a	H	H	H	3a (90)
2	1b/2b	4-Me	H	6-Me	3b (99)
3	1c/2c	H	4-Me	H	3c (99)
4	1d/2d	4-Me	4-Me	6-Me	3d (99)
5	1e/2e	4-MeO	H	6-MeO	3e (97) (97^b)
6	1f/2f	H	4-MeO	H	3f (97) (97^b)
7	1g/2g	3,4-Di(MeO)	H	5,6-Di(MeO)	3g (95) (98^b)
8	1h/2h	4-MeO	4-MeO	6-MeO	3h (10) (92^b)
9	1i/2i	4-Me	3,4-Di(MeO)	6-Me	3i (20) (50^b)
10^c	1j/2j	3,4-Di(Me)	H	5,6-Di(Me)	3j1 (53)
				6,7-Di(Me)	3j2 (43)
11	1k	2,4-Di(Me)	H	4,6-Di(Me)	3k (97)
12	1l	2,5-Di(Me)	H	4,7-Di(Me)	3l (97)
13	1m/2m	2,4,6-Tri(Me)	H	4,6,7-Tri(Me)	3m (97)
14	1n/2n	H	3,4-OCH2O	H	3n (68) (91^b)
15	1o/2o	H	4-Cl	H	3o (97)
16	1p	4-F	3,4-Di(Me)	6-F	3p (97)
17	1q	4-F	3,4-Di(MeO)	6-F	3q (74)^d

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Both CF₃-TMS-ethers 1 and CF₃-allyl alcohols 2 gave the same indenes with the same high yields (Table 1). In most of the cases, the formation of indenes 3a–q was quantitative (Table 1). However, in H₂SO₄ compounds 3h and 3i bearing donating methoxy groups were formed in low yields of 10 and 20%, respectively, due to the consequent transformations of these electron-rich indenes in H₂SO₄. The use of less acidic CF₃CO₂H resulted in much higher yields of 3h and 3i, 92 and 50%, respectively (entries 8 and 9).

It should be noted that starting compounds 1/2, bearing both electron withdrawing and donating substituents R¹, R² in aryl rings Ar¹, Ar², respectively, led to the exclusive formation of indenes 3, formed by the cyclization at carbon C⁴ in CF₃-allyl cations A (see Fig. 1). The formation of alternative indene structures by cyclization at carbon C² in species A was not observed at all. This regioselectivity in reactions of CF₃-cations A is contrary to the non-selective behaviour of other allyl cations without the CF₃-substituent.²⁰

Despite that indenes 3 were formed quantitatively without any further purification, under the attempt of their additional column chromatography isolation with silica gel, the isomerization into other indenes 4 was observed (Scheme 2). Thus, we developed the procedure for this quantitative isomerization by stirring a solution of compounds 3 in EtOAc in the presence of silica gel at room temperature for 4 h (see Scheme 2 for selected indenes 3/4). Compared with compounds 3, their isomers 4 should be thermodynamically more stable, because of the additional conjugation of the indene C²=C³ double bond with the aryl group Ar². Some of the indenes 3 were isomerized very easily. Thus, under the isolation (without column chromatography with silica gel) of 3q, the additional formation of the corresponding isomeric indene 4q was observed (entry 17, Table 1). On the other hand, polymethylated indenes 3j2, 3l and 3m, bearing a methyl group in the position 7 of the indene system, were not isomerized at all, presumably, because of the steric hindrance from this methyl substituent. Most likely, the presence of the substituent in the indene position 7 is a crucial point for this isomerization. Any bulky group in this position may disturb a flat orientation of ring Ar² relatively to the indene plane, which is thermodynamically favorable for conjugation of their π-systems. A shift of the double bond in the indene system with a formation of isomeric indenes has also been observed under the action of various basic or acidic reagents.^13,21–23

Scheme 2 Isomerization of CF₃-indenes 3 into 4 (see substituents R¹, R² in aryl rings Ar¹, Ar², respectively, in Table 1).

Conclusion

We have found a novel, effective and simple method for the synthesis of two series of isomeric CF₃-indenes based on acid (H₂SO₄ or CF₃CO₂H)-promoted cyclization of 2,4-diaryl-1,1,1-trifluorobut-3-en-2-oles or their TMS-ethers.

Experimental part

Instruments

The NMR spectra of solutions of compounds in CDCl₃ were recorded on a Bruker AVANCE III 400 (at 400, 376 and 100 MHz for ¹H, ¹⁹F and ¹³C NMR spectra, respectively) spectrometer at 25 °C. The residual proton-solvent peak CDCl₃ (δ 7.26 ppm) for ¹H NMR spectra and the carbon signal of CDCl₃ (δ 77.0 ppm) for ¹³C NMR spectra were used as references. ¹⁹F NMR spectra were indirectly referred to the signal of CFCl₃ (δ 0.0 ppm). HRMS was carried out with a Bruker maXis HRMS-ESI-QTOF and a Varian 902-MS MALDI mass spectrometer. Chromato-mass-spectrometry data were obtained using a Shimadzu QP-2010 Ultra equipped with a SPB-1 SULFUR capillary column (30 m × 0.32 mm), the thickness of the stationary phase being 1.25 μm. The preparative reactions were monitored by thin-layer chromatography carried out on silica gel plates (Alugram SIL G/UV-254), using UV light for detection. Preparative TLC was performed on silica gel Chemapol L 5/40 with the petroleum ether–ethyl acetate mixture as an eluent.

DFT calculations

All computations were carried out at the DFT/HF hybrid level of theory using the Becke's three-parameter hybrid exchange functional in combination with the gradient-corrected correlation functional of Lee, Yang, and Parr (B3LYP) by using GAUSSIAN 2009 program packages.²⁴ The geometry optimization was performed using the 6-311+G(2d,2p) basis set (standard 6-311 basis set added with polarization (d, p) and diffuse functions). Optimizations were performed on all degrees of freedom, and solvent-phase optimized structures were verified as true minima with no imaginary frequencies. The Hessian matrix was calculated analytically for the optimized structures in order to prove the location of correct minima and to estimate the thermodynamic parameters. Gibbs free energies were calculated at 25 °C. Solvent-phase calculations used the Polarizable Continuum Model (PCM).

Synthesis and characterization of compounds 1 and 2

Trifluoromethylation of chalcones with CF₃SiMe₃ leading to compounds 1 was carried out according to the literature procedures.^25,26 Detrimethylsilylation of compounds 1 giving alcohols 2 was carried out with aqueous HCl²⁵ or with SnCl₂.²⁷

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2,4-diphenylbut-3-en-2-ol (1a). Yield 82%. Colorless solid. M.p. 49–50 °C (oil lit.^25,26). ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.16 s (9H, SiMe₃), 6.56 d (1H, =CH, J 16.3 Hz), 6.71 d (1H, =CH, J 16.3 Hz), 7.29–7.43 m (8H_arom.), 7.60–7.62 m (2H_arom.). ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −77.40 s (CF₃). HRMS: C₁₉H₂₁F₃OSiAg found 457.0360 [M + Ag]⁺; calcd 457.0359.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2-(4-methylphenyl)-4-phenylbut-3-en-2-ol (1b). Yield 96%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.15 s (9H, SiMe₃), 2.39 s (3H, Me), 6.56 d (1H, =CH, J 16.3 Hz), 6.72 d (1H, =CH, J 16.3 Hz), 7.21 d (2H_arom., J 8.1 Hz), 7.29–7.43 m (5H_arom.), 7.49 d (2H_arom., J 8.1 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.2 (SiMe₃), 21.2 (Me), 80.0 q (C², J_C–F 28.8 Hz), 125.2 q (CF₃, J_C–F 286.8 Hz), 127.0, 127.2, 128.0, 128.7, 128.8, 128.9, 135.2, 135.2, 135.9, 138.5. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −77.57 s (CF₃). HRMS: C₂₀H₂₃F₃OSiAg found 471.0517 [M + Ag]⁺; calcd 471.0516.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-4-(4-methylphenyl)-2-phenylbut-3-en-2-ol (1c). Yield 92%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.16 s (9H, SiMe₃), 2.37 s (3H, Me), 6.52 d (1H, =CH, J 16.4 Hz), 6.66 d (1H, =CH, J 16.4 Hz), 7.17 d (2H_arom., J 8.0 Hz), 7.31 d (2H_arom., J 8.0 Hz), 7.36–7.43 m (3H_arom.), 7.60–7.62 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.2 (SiMe₃), 21.4 (Me), 80.1 q (C², J_C–F 28.8 Hz), 125.2 q (CF₃, J_C–F 286.6 Hz), 126.0, 126.9, 128.0, 128.1, 128.6, 129.7, 133.1, 135.4, 138.2, 138.8. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −77.57 s (CF₃). HRMS: C₂₀H₂₃F₃OSiAg found 471.0507 [M + Ag]⁺; calcd 471.0516.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2,4-bis(4-methylphenyl)but-3-en-2-ol (1d). Yield 99%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.15 s (9H, SiMe₃), 2.36 s (3H, Me), 2.39 s (3H, Me), 6.51 d (1H, =CH, J 16.3 Hz), 6.67 d (1H, =CH, J 16.3 Hz), 7.17 d (2H_arom., J 8.0 Hz), 7.20 d (2H_arom., J 8.1 Hz), 7.31 d (2H_arom., J 8.0 Hz), 7.49 d (2H_arom., J 8.1 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.2 (SiMe₃), 21.2 (Me), 21.4 (Me), 80.0 q (C², J_C–F 28.7 Hz), 125.2 q (CF₃, J_C–F 286.6 Hz), 126.1, 126.9, 128.1, 128.8, 129.6, 133.2, 135.2, 135.3, 138.4, 138.7. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −77.75 c (CF₃). HRMS: C₂₁H₂₅F₃OSiAg found 485.0668 [M + Ag]⁺; calcd 485.0672.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2-(4-methoxyphenyl)-4-phenylbut-3-en-2-ol (1e). Yield 98%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.18 s (9H, SiMe₃), 3.83 s (3H, OMe), 6.46 d (1H, =CH, J 16.3 Hz), 6.64 d (1H, =CH, J 16.3 Hz), 6.91 d (2H_arom., J 8.7 Hz), 7.37 d (2H_arom., J 8.7 Hz), 7.40–7.42 m (3H_arom.), 7.63–7.65 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.2 (SiMe₃), 55.4 (OMe), 80.2 q (C², J 28.8 Hz), 114.4, 124.7, 125.2 q (CF₃, J 286.5 Hz), 128.0, 128.2, 128.3, 128.6, 128.6, 135.1, 138.3, 160.2. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −77.64 c (CF₃). HRMS: C₂₀H₂₃F₃O₂SiAg found 487.0469 [M + Ag]⁺; calcd 487.0465.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-4-(4-methoxyphenyl)-2-phenylbut-3-en-2-ol (1f). Yield 99%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.15 s (9H, SiMe₃), 3.85 s (3H, OMe), 6.56 d (1H, =CH, J 16.3 Hz), 6.73 d (1H, =CH, J 16.3 Hz), 6.93 d (2H_arom., J 8.6 Hz), 7.30–7.37 m (3H_arom.), 7.42–7.44 m (2H_arom.), 7.53 d (2H_arom., J 8.6 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.2 (SiMe₃), 55.4 (OMe), 79.8 q (C², J_C–F 28.9 Hz), 113.4, 125.2 q (CF₃, J_C–F 286.5 Hz), 127.0, 127.2, 128.7, 128.9, 129.5, 130.0, 135.2, 135.9, 159.9. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −77.73 c (CF₃). HRMS: C₂₀H₂₃F₃O₂SiAg found 487.0477 [M + Ag]⁺; calcd 487.0465.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2-(3,4-dimethoxyphenyl)-2-phenylbut-3-en-2-ol (1g). Yield 99%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.15 s (9H, SiMe₃), 3.88 s (3H, OMe), 3.91 s (3H, OMe), 6.55 d (1H, =CH, J 16.3 Hz), 6.71 d (1H, =CH, J 16.3 Hz), 6.88 d (1H_arom., J 9.0 Hz), 7.14–7.15 m (2H_arom.), 7.26–7.43 m (5H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.2 s (SiMe₃), 56.0 (OMe), 56.0 (OMe), 79.9 q (C², J_C–F 28.7 Hz), 110.5, 111.6, 120.8, 125.2 q (CF₃, J_C–F 287.0 Hz), 127.0, 127.0, 128.8, 129.0, 130.4, 135.4, 135.9, 148.5, 149.3. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −77.64 c (CF₃). HRMS: C₂₁H₂₅F₃O₂SiAg found 517.0559 [M + Ag]⁺; calcd 517.0571.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2,4-bis(4-methoxyphenyl)but-3-en-2-ol (1h). Yield 95%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.14 s (9H, SiMe₃), 3.82 s (3H, OMe), 3.84 s (3H, OMe), 6.41 d (1H, =CH, J 16.3 Hz), 6.62 d (1H, =CH, J 16.3 Hz), 6.89 d (2H_arom., J 8.7 Hz), 6.92 d (2H_arom., J 8.8 Hz), 7.35 d (2H_arom., J 8.7 Hz), 7.52 d (2H_arom., J 8.8 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.2 (SiMe₃), 55.4 (OMe), 55.5 (OMe), 79.9 q (C², J_C–F 29.0 Hz), 113.4, 114.4, 124.9, 125.3 q (CF₃, J_C–F 286.6 Hz), 128.3, 128.6, 129.5, 130.2, 134.9, 159.8, 160.2. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.02 c (CF₃). HRMS: C₂₁H₂₅F₃O₂SiAg found 517.0550 [M + Ag]⁺; calcd 517.0571.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2-(4-methylphenyl)-4-(3,4-dimethoxyphenyl)but-3-en-2-ol (1i). Yield 99%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.14 s (9H, SiMe₃), 2.39 s (3H, Me), 3.89 s (3H, OMe), 3.91 s (3H, OMe), 6.40 d (1H, =CH, J 16.3 Hz), 6.61 d (1H, =CH, J 16.3 Hz), 6.85 d (1H_arom., J 8.3 Hz), 6.93 d (1H_arom., J 1.9 Hz), 6.96 dd (1H_arom., J 8.3 Hz, J 1.9 Hz), 7.21 d (2H_arom., J 8.1 Hz), 7.49 d (2H_arom., J 8.1 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.2 (SiMe₃), 21.2 (Me), 56.1 (OMe), 56.1 (OMe), 80.1 q (C², J 28.8 Hz), 104.4, 109.4, 111.4, 120.3, 125.1, 125.2 q (CF₃, J_C–F 286.5 Hz), 128.1, 128.8, 128.9, 135.1, 135.2, 138.4, 149.4, 149.8. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −77.68 (CF₃). HRMS: C₂₂H₂₇F₃O₃SiAg found 531.0727 [M + Ag]⁺; calcd 531.0731.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2-(3,4-dimethylphenyl)-2-phenylbut-3-en-2-ol (1j). Yield 93%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.15 s (9H, SiMe₃), 2.30 s (6H, 2Me), 6.55 d (1H, =CH, J 16.3 Hz), 6.73 d (1H, =CH, J 16.3 Hz), 7.16 d (1H_arom., J 7.8 Hz), 7.29–7.39 m (5H_arom.), 7.42–7.44 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.2 (SiMe₃), 19.6 (Me), 20.2 (Me), 80.0 q (C², J_C–F 28.8 Hz), 125.2 q (CF₃, J_C–F 286.7 Hz), 125.5, 127.0, 127.3, 128.7, 128.9, 129.2, 129.4, 135.0, 135.5, 136.0, 136.2, 137.1. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −77.41 c (CF₃). HRMS: C₂₁H₂₅F₃OSiAg found 485.0668 [M + Ag]⁺; calcd 485.0672.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2-(2,4-dimethylphenyl)-2-phenylbut-3-en-2-ol (1k). Yield 94%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.09 s (9H, SiMe₃), 2.33 s (3H, Me), 2.39 s (3H, Me), 6.47 d (1H, =CH, J 16.4 Hz), 6.67 d (1H, =CH, J 16.4 Hz), 7.01–7.03 m (2H_arom.), 7.27–7.42 m (5H_arom.), 7.50 d (1H_arom., J 7.7 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 1.8 (SiMe₃), 21.0 (Me), 22.6 (Me), 81.0 q (C², J_C–F 28.5 Hz), 125.6 q (CF₃, J_C–F 287.4 Hz), 126.2, 126.9, 128.3, 128.5, 128.9, 133.7, 133.8, 134.1, 136.2, 138.0, 138.3. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −74.50 c (CF₃). HRMS: C₂₁H₂₅F₃OSiAg found 485.0664 [M + Ag]⁺; calcd 485.0672.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2-(2,5-dimethylphenyl)-2-phenylbut-3-en-2-ol (1l). Yield 97%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.09 s (9H, SiMe₃), 2.36 s (3H, Me), 2.38 s (3H, Me), 6.47 d (1H, =CH, J 16.4 Hz), 6.68 d (1H, =CH, J 16.4 Hz), 7.08 m (2H_arom.), 7.28–7.37 m (3H_arom.), 7.40–7.42 m (3H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 1.7 (SiMe₃), 21.3 (Me), 22.2 (Me), 81.0 q (C², J_C–F 28.6 Hz), 125.5 q (CF₃, J_C–F 287.6 Hz), 126.8, 128.1, 128.4, 128.8, 129.0, 129.2, 132.8, 134.1, 134.7, 134.9, 136.1, 136.2. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −74.24 c (CF₃). HRMS: C₂₁H₂₅F₃OSiAg found 485.0662 [M + Ag]⁺; calcd 485.0672.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2-(2,4,6-trimethylphenyl)-2-phenylbut-3-en-2-ol (1m). Yield 99%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.10 s (9H, SiMe₃), 2.25 s (3H, Me), 2.27 s (3H, Me), 2.36 s (3H, Me), 6.48 d (1H, =CH, J 16.4 Hz), 6.69 d (1H, =CH, J 16.4 Hz), 6.97 s (1H_arom.), 7.27–7.43 m (6H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 1.7 (SiMe₃), 19.2 (Me), 19.5 (Me), 22.0 (Me), 80.8 q (C², J_C–F 28.5 Hz), 125.4 q (CF₃, J_C–F 287.6 Hz), 126.7, 128.2, 128.3, 128.7, 129.6, 133.2, 133.6, 133.9, 134.2, 135.1, 136.1, 136.7. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −74.54 c (CF₃). HRMS: C₂₂H₂₇F₃OSiAg found 499.0834 [M + Ag]⁺; calcd 499.0829.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-4-(3,4-methylenedioxyphenyl)-2-phenylbut-3-en-2-ol (1n). Yield 99%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.16 s (9H, SiMe₃), 5.98 s (2H, CH₂), 6.39 d (1H, =CH, J 16.2 Hz), 6.59 d (1H, =CH, J 16.2 Hz), 6.78 d (1H_arom., J 8.0 Hz), 6.83 d (1H_arom., J 8.0 Hz), 6.96 s (1H_arom.), 7.36–7.42 m (3H_arom.), 7.59–7.61 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.2 (SiMe₃), 80.1 q (C², J_C–F 28.8 Hz), 101.4, 105.9, 108.6, 122.2, 125.2 q (CF₃, J_C–F 286.3 Hz), 125.2, 128.0, 128.1, 128.6, 130.3, 135.2, 138.2, 148.3, 148.5. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −77.59 c (CF₃). HRMS: C₂₀H₂₁F₃O₃SiAg found 501.0252 [M + Ag]⁺; calcd 501.0258.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-4-(4-chlorophenyl)-2-phenylbut-3-en-2-ol (1o). Yield 99%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.15 s (9H, SiMe₃), 6.53 d (1H, =CH, J 16.3 Hz), 6.67 d (1H, =CH, J 16.3 Hz), 7.34 s (4H_arom.), 7.38–7.43 m (3H_arom.), 7.59–7.61 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.1 (SiMe₃), 80.1 q (C², J_C–F 29.0 Hz), 125.1 q (CF₃, J_C–F 286.8 Hz), 127.9, 128.0, 128.2, 128.2, 128.8, 129.2, 133.9, 134.4, 134.6, 138.0. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −77.19 c (CF₃). HRMS: C₂₁H₂₅F₃³⁵ClOSiAg found 490.9965 [M + Ag]⁺; calcd 490.9969.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2-(4-fluorophenyl)-4-(3,4-dimethylphenyl)but-3-en-2-ol (1p). Yield 96%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.17 s (9H, SiMe₃), 2.28 s (6H, 2Me), 6.50 d (1H, =CH, J 16.4 Hz), 6.61 d (1H, =CH, J 16.4 Hz), 7.05–7.18 m (5H_arom.), 7.59 dd (2H_arom., J 8.6 Hz, J 5.5 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.1 (SiMe₃), 19.6 (Me), 19.8 (Me), 79.8 q (C², J_C–F 29.0 Hz), 114.8 d (J_C–F 21.5 Hz), 124.3, 125.1 q (CF₃, J_C–F 286.6 Hz), 125.3, 128.3, 130.1 d (J 8.2 Hz), 130.2, 133.2, 134.1 d (J_C–F 3.1 Hz), 135.9, 137.2, 137.7, 162.9 d (J_C–F 247.6 Hz). ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −113.96 c (1F_arom.), −77.95 c (CF₃). HRMS: C₂₁H₂₄F₄OSiAg found 503.0570 [M + Ag]⁺; calcd 503.0578.

Trimethylsilyl ether of (E)-1,1,1-trifluoro-2-(4-fluorophenyl)-4-(3,4-dimethoxyphenyl)but-3-en-2-ol (1q). Yield 93%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 0.16 s (9H, SiMe₃), 3.90 s (3H, OMe), 3.91 s (3H, OMe), 6.39 d (1H, =CH, J 16.3 Hz), 6.57 d (1H, =CH, J 16.3 Hz), 6.85 d (1H_arom., J 8.3 Hz), 6.92 d (1H_arom., J 1.9 Hz), 6.96 dd (1H_arom., J 8.3 Hz, J 1.9 Hz), 7.05–7.11 m (2H_arom.), 7.58 dd (2H_arom., J 8.6 Hz, J 5.4 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 2.1 s (SiMe₃), 56.1 (OMe), 56.1 (OMe), 79.8 q (C², J_C–F 29.0 Hz), 109.3, 111.4, 114.9 d (J_C–F 21.5 Hz), 120.4, 124.6, 125.1 q (CF₃, J_C–F 286.3 Hz), 128.6, 130.1 d (J_C–F 8.3 Hz), 134.0 d (J_C–F 3.2 Hz), 135.6, 149.4, 150.0, 163.0 d (J_C–F 247.7 Hz). ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −113.88 c (1F_arom.), −77.90 c (CF₃). HRMS: C₂₁H₂₄F₄O₃SiAg found 535.0484 [M + Ag]⁺; calcd 535.0476.

(E)-1,1,1-Trifluoro-2,4-diphenylbut-3-en-2-ol (2a). Yield 95%. Yellow oil (oil lit.²⁴). ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.69 s (1H, OH), 6.73 d (1H, =CH, J 16.1 Hz), 6.89 d (1H, =CH, J 16.1 Hz), 7.28–7.45 m (8H_arom.), 7.65–7.67 m (2H_arom.). ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.50 c (CF₃). HRMS: C₁₆H₁₃F₃OAg found 384.9957 [M + Ag]⁺; calcd 384.9964.

(E)-1,1,1-Trifluoro-2-(4-methylphenyl)-4-phenylbut-3-en-2-ol (2b). Yield 94%. Yellow solid. M.p. 53–55 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.38 s (3H, Me), 2.66 s (1H, OH), 6.72 d (1H, =CH, J 16.1 Hz), 6.89 d (1H, =CH, J 16.1 Hz), 7.23 d (2H_arom., J 8.1 Hz), 7.28–7.38 m (3H_arom.), 7.43–7.45 m (2H_arom.), 7.54 d (2H_arom., J 8.1 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 21.21 (Me), 77.4 q (C², J_C–F 29.0 Hz), 125.2 q (CF₃, J_C–F 286.0 Hz), 126.7, 126.9, 126.9, 127.1, 128.7, 128.9, 129.2, 133.5, 134.6, 135.7, 138.9. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.57 c (CF₃). HRMS: C₁₇H₁₅F₃OAg found 399.0124 [M + Ag]⁺; calcd 399.0120.

(E)-1,1,1-Trifluoro-4-(4-methylphenyl)-2-phenylbut-3-en-2-ol (2c). Yield 92%. Yellow solid. M.p. 64–66 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.36 s (3H, Me), 2.67 s (1H, OH), 6.68 d (1H, =CH, J 16.1 Hz), 6.85 d (1H, =CH, J 16.1 Hz), 7.16 d (2H_arom., J 8.0 Hz), 7.33 d (2H_arom., J 8.0 Hz), 7.37–7.44 m (3H_arom.), 7.65–7.67 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 21.4 (Me), 77.5 q (C², J_C–F 29.0 Hz), 125.2 q (CF₃, J_C–F 286.0 Hz), 125.6, 127.0, 127.0, 128.5, 128.9, 129.6, 132.9, 133.6, 137.6, 138.8. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.55 c (CF₃). HRMS: C₁₇H₁₅F₃OAg found 399.0110 [M + Ag]⁺; calcd 399.0120.

(E)-1,1,1-Trifluoro-2,4-bis(4-methylphenyl)but-3-en-2-ol (2d). Yield 80%. Yellow solid. M.p. 49–51 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.36 s (3H, Me), 2.38 s (3H, Me), 2.58 s (1H, OH), 6.66 d (1H, =CH, J 16.1 Hz), 6.84 d (1H, =CH, J 16.1 Hz), 7.16 d (2H_arom., J 8.0 Hz), 7.22 d (2H_arom., J 8.1 Hz), 7.32 d (2H_arom., J 8.0 Hz), 7.53 d (2H_arom., J 8.1 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 21.2 (Me), 21.4 (Me), 77.4 q (C², J_C–F 28.6 Hz), 125.3 q (CF₃, J 286.2 Hz), 125.7, 126.9, 127.0, 129.2, 129.6, 132.9, 133.5, 134.7, 138.7, 138.8. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.65 c (CF₃). HRMS: C₁₈H₁₇F₃OAg found 413.0267 [M + Ag]⁺; calcd 413.0277.

(E)-1,1,1-Trifluoro-2-(4-methoxyphenyl)-4-phenylbut-3-en-2-ol (2e). Yield 94%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.69 s (1H, OH), 3.82 s (3H, OCH₃), 6.59 d (1H, =CH, J 16.1 Hz), 6.81 d (1H, =CH, J 16.1 Hz), 6.88 d (2H_arom., J 8.8 Hz), 7.35–7.44 m (5H_arom.), 7.64–7.66 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 55.5 (OMe), 77.5 q (C², J_C–F 28.6 Hz), 114.3, 124.4, 125.3 q (CF₃, J 285.9 Hz), 127.0, 128.4, 128.4, 128.5, 128.9, 133.3, 137.7, 160.2. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.57 c (CF₃). HRMS: C₁₇H₁₅F₃O₂Ag found 415.0089 [M + Ag]⁺; calcd 415.0070.

(E)-1,1,1-Trifluoro-4-(4-methoxylphenyl)-2-phenylbut-3-en-2-ol (2f). Yield 61%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.66 s (1H, OH), 3.82 s (3H, OMe), 6.58 d (1H, =CH, J 16.1 Hz), 6.80 d (1H, =CH, J 16.1 Hz), 6.87 d (2H_arom., J 8.8 Hz), 7.35–7.43 m (5H_arom.), 7.64–7.65 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 55.5 (OMe), 77.5 q (C², J_C–F 28.9 Hz), 114.3, 124.4, 125.3 q (CF₃, J_C–F 286.1 Hz), 127.0, 128.3, 128.4, 128.4, 128.8, 133.3, 137.8, 160.1. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.59 c (CF₃). HRMS: C₁₇H₁₅F₃O₂Ag found 415.0073 [M + Ag]⁺; calcd 415.0070.

(E)-1,1,1-Trifluoro-2-(3,4-dimethoxyphenyl)-2-phenylbut-3-en-2-ol (2g). Yield 93%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.76 s (1H, OH), 3.89 s (3H, OMe), 3.90 s (3H, OMe), 6.69 d (1H, =CH, J 16.1 Hz), 6.88 d (1H, =CH, J 16.1 Hz), 6.88 d (1H_arom., J 8.5 Hz), 7.16 d (1H_arom., J 8.5 Hz), 7.19 s (1H_arom.), 7.28–7.37 m (3H_arom.), 7.43 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 56.0 (OMe), 56.1 (OMe), 77.5 q (C², J 28.6 Hz), 110.3, 110.8, 119.8, 125.3 q (CF₃, J_C–F 286.1 Hz), 126.7, 127.0, 128.8, 128.9, 129.9, 133.7, 135.7, 148.9, 149.5. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.54 c (CF₃). HRMS: C₁₈H₁₇F₃O₃Ag found 445.0178 [M + Ag]⁺; calcd 445.0175.

(E)-1,1,1-Trifluoro-2,4-bis(4-methoxyphenyl)but-3-en-2-ol (2h). Yield 99%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.73 s (1H, OH), 3.81 s (3H, OMe), 3.82 s (3H, OMe), 6.56 d (1H, =CH, J 16.1 Hz), 6.79 d (1H, =CH, J 16.1 Hz), 6.87 d (2H_arom., J 8.7 Hz), 6.92 d (2H_arom., J 8.8 Hz), 7.36 d (2H_arom., J 8.7 Hz), 7.56 d (2H_arom., J 8.8 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 55.4 (OMe), 55.5 (OMe), 77.2 q (C², J_C–F 28.6 Hz), 113.8, 114.3, 124.5, 125.3 q (CF₃, J_C–F 286.0 Hz), 128.3, 128.5, 129.8, 133.1, 159.9, 160.1. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.77 c (CF₃). HRMS: C₁₈H₁₇F₃O₃Ag found 445.0173 [M + Ag]⁺; calcd 445.0175.

(E)-1,1,1-Trifluoro-2-(4-methylphenyl)-4-(3,4-dimethoxyphenyl)but-3-en-2-ol (2i). Yield 95%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.37 s (3H, Me), 2.71 s (1H, OH), 3.88 s (3H, OMe), 3.90 s (3H, OMe), 6.55 d (1H, =CH, J 16.0 Hz), 6.79 d (1H, =CH, J 16.0 Hz), 6.83 d (1H_arom., J 8.1 Hz), 6.95–6.97 m (2H_arom.), 7.22 d (2H_arom., J 8.1 Hz), 7.53 d (2H_arom., J 8.1 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 21.2 (Me), 56.1 (OMe), 56.1 (OMe), 77.4 q (C², J 28.8 Hz), 109.4, 111.3, 120.5, 124.7, 125.3 q (CF₃, J_C–F 285.8 Hz), 126.9, 128.8, 129.2, 133.5, 134.8, 138.8, 149.3, 149.8. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.49 c (CF₃). HRMS: C₁₉H₁₉F₃O₃Ag found 459.0328 [M + Ag]⁺; calcd 459.0332.

(E)-1,1,1-Trifluoro-2-(3,4-dimethylphenyl)-2-phenylbut-3-en-2-ol (2j). Yield 93%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.28 s (3H, Me), 2.30 s (3H, Me), 2.61 s (1H, OH), 6.70 d (1H, =CH, J 16.1 Hz), 6.89 d (1H, =CH, J 16.1 Hz), 7.17 d (1H_arom., J 8.0 Hz), 7.27–7.36 m (4H_arom.), 7.40 s (1H_arom.), 7.42–7.44 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 19.5 (Me), 20.1 (Me), 77.3 q (C², J_C–F 28.8 Hz), 124.3, 125.3 q (CF₃, J_C–F 286.0 Hz), 126.9, 127.0, 127.9, 128.6, 128.8, 129.7, 133.2, 135.1, 135.9, 136.8, 137.4. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.50 c (CF₃). HRMS: C₁₈H₁₇F₃OAg found 413.0269 [M + Ag]⁺; calcd 413.0277.

(E)-1,1,1-Trifluoro-2-(2,4,6-trimethylphenyl)-2-phenylbut-3-en-2-ol (2m). Yield 94%. Yellow solid. M.p. 66–68 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.25 s (3H, Me), 2.28 s (3H, Me), 2.41 s (3H, Me), 2.55 s (1H, OH), 6.67 d (1H, =CH, J 16.2 Hz), 6.75 d (1H, =CH, J 16.2 Hz), 6.99 s (1H_arom.), 7.27–7.37 m (3H_arom.), 7.42–7.43 m (3H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 19.3 (Me), 19.6 (Me), 22.0 q (Me, J 1.2 Hz), 78.9 q (C², J_C–F 28.6 Hz), 125.7 q (CF₃, J_C–F 286.7 Hz), 126.9, 127.5, 128.6, 128.9, 129.2, 132.8, 133.7, 134.0, 134.5, 135.1, 135.9, 137.4. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −76.72 c (CF₃). HRMS: C₁₉H₁₉F₃OAg found 427.0422 [M + Ag]⁺; calcd 427.0433.

(E)-1,1,1-Trifluoro-4-(3,4-methylenedioxyphenyl)-2-phenylbut-3-en-2-ol (2n). Yield 72%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.70 s (1H, OH), 5.97 s (2H, CH₂) 6.54 d (1H, =CH, J 16.0 Hz), 6.77 d (1H_arom., J 8.1 Hz), 6.77 d (1H, =CH, J 16.0 Hz), 6.85 dd (1H_arom., J 8.1 Hz, J 1.5 Hz), 6.97 d (1H_arom., J 1.5 Hz), 7.36–7.43 m (3H_arom.), 7.63–7.64 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 77.4 q (C², J 29.2 Hz), 101.4, 106.1, 108.5, 122.2, 124.8, 125.2 q (CF₃, J_C–F 285.8 Hz), 127.0, 128.5, 128.9, 130.1, 133.4, 137.6, 148.2, 148.4. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.57 c (CF₃). HRMS: C₁₇H₁₃F₃O₃Ag found 428.9867 [M + Ag]⁺; calcd 428.9863.

(E)-1,1,1-Trifluoro-4-(4-chlorophenyl)-2-phenylbut-3-en-2-ol (2o). Yield 93%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.69 s (1H, OH), 6.68 d (1H, =CH, J 16.0 Hz), 6.85 d (1H, =CH, J 16.0 Hz), 7.30–7.45 m (7H_arom.), 7.63–7.65 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 77.5 q (C², J_C–F 29.1 Hz), 125.1 q (CF₃, J_C–F 286.0 Hz), 126.8, 127.2, 128.3, 128.6, 129.0, 132.5, 134.2, 134.5, 137.4. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −78.40 c (CF₃). HRMS: C₁₆H₁₂F₃³⁵ClOAg found 418.9557 [M + Ag]⁺; calcd 418.9574.

Synthesis and characterization of indenes 3

General procedure for cyclization of compounds 1 or 2 into indenes 3 in H₂SO₄. 1 mL of H₂SO₄ (95%) was added in one portion to a solution of 0.1 mmol of compound 1 or 2 in 1 mL of CH₂Cl₂ at room temperature with vigorous stirring. The reaction mixture was stirred for 2 min, then poured into 15 mL of water, and extracted with CH₂Cl₂ (3 × 15 mL). The combined extracts were washed with water (3 × 10 mL), dried over Na₂SO₄. Evaporation of the solvent under reduced pressure finally gave indene 3. Analogously the reactions were carried out in CF₃CO₂H (see Table 1).

3-(Trifluoromethyl)-1-phenyl-1H-indene (3a). Yield 90%. Yellow solid. M.p. 43–45 °C (oil lit.¹³). ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 4.74 m (1H, C¹H), 7.03 m (1H, =CH), 7.12 d (2H_arom., J 7.6 Hz), 7.28–7.33 m (5H_arom.), 7.38 t (1H_arom., J 7.4 Hz), 7.57 d (1H_arom., J 7.6 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 55.6 (C¹), 121.2, 122.5 q (CF₃, J 270.0 Hz), 123.9, 126.6, 127.0, 127.6, 128.03, 129.1, 134.6 q (C³, J 34.3 Hz), 137.1, 138.2, 141.0 q (C², J 5.0 Hz), 148.0. ¹⁹F {1H} NMR (CDCl₃, 376 MHz) δ, ppm: −64.05 s (CF₃). HRMS (MALDI): C₁₆H₁₂F₃ found 261.0886 [M + H]⁺, calcd 261.0891.

3-(Trifluoromethyl)-6-methyl-1-phenyl-1H-indene (3b). Yield 99%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.36 c (3H, Me), 4.69 m (1H, C¹H), 6.95 m (1H, =CH), 7.12 d (2H_arom., J 8.0 Hz), 7.13 c (1H_arom.), 7.19 d (1H_arom., J 7.8 Hz), 7.28–7.34 m (3H_arom.), 7.44 d (1H_arom., J 7.8 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 21.6 (Me), 55.4 (C¹), 120.6, 122.6 q (CF₃, J 270.0 Hz), 125.3, 127.5, 128.1, 128.3, 129.1, 134.5 q (C³, J 34.2 Hz), 135.5 d (C^3a, J 1.1 Hz), 137.0, 137.4 d (C^7a, J 0.8 Hz), 140.0 q (C², J 5.1 Hz), 148.4. ¹⁹F {1H} NMR (CDCl₃, 376 MHz) δ, ppm: −64.07 s (CF₃). HRMS (MALDI): C₁₇H₁₄F₃ found 275.1042 [M + H]⁺, calcd 275.1048.

3-(Trifluoromethyl)-1-(4-methylphenyl)-1H-indene (3c). Yield 99%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.34 c (3H, Me), 4.71 m (1H, C¹H), 7.00 d (2H_arom., J 8.1 Hz), 7.01 m (1H, =CH), 7.12 d (2H_arom., J 8.1 Hz), 7.26–7.32 m (2H_arom.), 7.37 t.d (1H_arom., J 7.6 Hz, J 1.5 Hz), 7.56 d (1H_arom., J 7.6 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 21.2 (Me), 55.3 (C¹), 120.9, 122.6 q (CF₃, J 270.0 Hz), 124.5, 126.9, 127.4, 127.9, 129.8, 133.9, 134.4 q (C³, J 34.2 Hz), 137.3, 138.2, 141.3 q (C², J 5.0 Hz), 148.2. ¹⁹F {1H} NMR (CDCl₃, 376 MHz) δ, ppm: −64.02 s (CF₃). HRMS (MALDI): C₁₇H₁₄F₃ found 275.1042 [M + H]⁺, calcd 275.1038.

3-(Trifluoromethyl)-6-methyl-1-(4-methylphenyl)-1H-indene (3d). Yield 99%. Yellow solid. M.p. 101–103 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.35 c (3H, Me), 2.36 c (3H, Me), 4.66 m (1H, C¹H), 6.93 m (1H, =CH), 7.00 d (2H_arom., J 7.8 Hz), 7.12 s (1H_arom.), 7.13 d (2H_arom., J 7.8 Hz), 7.18 d (1H_arom., J 7.9 Hz), 7.43 d (1H_arom., J 7.9 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 21.2 (Me), 21.6 (Me), 55.1 (C¹), 120.5, 122.6 q (CF₃, J 270.0 Hz), 125.3, 127.9, 128.2, 129.8, 134.3, 134.3 q (C³, J 34.2 Hz), 135.5, 137.0, 137.2, 140.2 q (C², J 5.1 Hz). ¹⁹F {1H} NMR (CDCl₃, 376 MHz) δ, ppm: −64.05 s (CF₃). HRMS (MALDI): C₁₈H₁₆F₃ found 289.1199 [M + H]⁺, calcd 289.1210.

3-(Trifluoromethyl)-6-methoxy-1-phenyl-1H-indene (3e). Yield 97%. Yellow solid. M.p. 77–79 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 3.79 c (3H, OMe), 4.69 m (1H, C¹H), 6.84 d (2H_arom., J 8.6 Hz), 6.99 m (1H, =CH), 7.01 d (2H_arom., J 8.6 Hz), 7.25–7.30 m (2H_arom.), 7.37 m (1H_arom.), 7.54 d (1H_arom., J 7.5 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 54.9 (C¹), 55.4 (OMe), 114.5, 120.9, 122.6 q (CF₃, J 270.0 Hz), 124.5, 126.9, 127.4, 128.8, 129.0, 134.3 q (C³, J 34.2 Hz), 138.1, 141.4 q (C², J 5.0 Hz), 148.3, 159.1. ¹⁹F {1H} NMR (CDCl₃, 376 MHz) δ, ppm: −64.03 s (CF₃). HRMS (MALDI): C₁₇H₁₄F₃O found 291.0991 [M + H]⁺, calcd 291.0998.

3-(Trifluoromethyl)-1-(4-methoxyphenyl)-1H-indene (3f). Yield 97%. Yellow solid. M.p. 81–82 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 3.79 c (3H, OMe), 4.69 m (1H, C¹H), 6.84 d (2H_arom., J 8.7 Hz), 7.00 m (1H, =CH), 7.02 d (2H_arom., J 8.7 Hz), 7.25–7.31 m (2H_arom.), 7.36 m (1H_arom.), 7.55 d (1H_arom., J 7.6 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 54.9 (C¹), 55.4 (OMe), 114.5, 120.9, 122.6 q (CF₃, J 270.0 Hz), 124.5, 126.9, 127.4, 128.8, 129.0, 134.3 q (C³, J 34.2 Hz), 138.1, 141.4 q (C², J 5.0 Hz), 148.3, 159.1. ¹⁹F {1H} NMR (CDCl₃, 376 MHz) δ, ppm: −64.02 s (CF₃). HRMS (MALDI): C₁₇H₁₄F₃O found 291.0991 [M + H]⁺, calcd 291.1002.

3-(Trifluoromethyl)-5,6-dimethoxy-1-phenyl-1H-indene (3g). Yield 95%. Yellow solid. M.p. 60–62 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 3.81 c (3H, OMe), 3.95 c (3H, OMe), 4.65 m (1H, C¹H), 6.84 c (1H_arom.), 6.90 m (1H, =CH), 7.05 c (1H_arom.), 7.08–7.10 m (2H_arom.), 7.27–7.33 m (3H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 55.6 (C¹), 56.3 (OMe), 56.4 (OMe), 104.0, 108.1, 122.6 q (CF₃, J 269.9 Hz), 127.5, 128.0, 129.1, 130.8, 134.0 q (C³, J 34.1 Hz), 137.4, 139.8 q (C², J 5.2 Hz), 140.9, 149.0. ¹⁹F {1H} NMR (CDCl₃, 376 MHz) δ, ppm: −63.95 s (CF₃). HRMS (MALDI): C₁₈H₁₆F₃O₂ found 321.1097 [M + H]⁺, calcd 321.1095.

3-(Trifluoromethyl)-6-methoxy-1-(4-methoxyphenyl)-1H-indene (3h). Yield 92%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 3.77 c (3H, OMe), 3.79 c (3H, OMe), 4.63 m (1H, C¹H), 6.84 d (2H_arom., J 8.6 Hz), 6.85 m (=CH + 1H_arom.), 6.89 dd (1H_arom., J 8.3 Hz, J 2.3 Hz), 7.01 d (2H_arom., J 8.6 Hz), 7.42 d (H_arom., J 8.4 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 54.8 (C¹), 55.4 (OMe), 55.7 (OMe), 110.9, 113.0, 114.5, 121.4, 122.6 q (CF₃, J 269.9 Hz), 129.0, 129.2, 131.0, 133.8 q (C³, J 34.1 Hz), 139.2 q (C², J 5.1 Hz), 150.4, 159.1, 159.5. ¹⁹F {1H} NMR (CDCl₃, 376 MHz) δ, ppm: −64.11 s (CF₃). HRMS (MALDI): C₁₈H₁₆F₃O₂ found 321.1097 [M + H]⁺, calcd 321.1115.

3-(Trifluoromethyl)-6-methyl-1-(3,4-dimethoxyphenyl)-1H-indene (3i). Yield 50%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.44 c (3H, Me), 3.88 c (6H, 2OMe), 4.67 m (1H, C¹H), 6.92 m (1H, =CH), 7.2–7.5 m (6H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 21.4 (Me), 42.2 (C¹), 56.1 (2OMe), 111.3, 120.4, 123.5 q (CF₃, J 273.3Hz), 125.3, 127.6, 129.8, 130.2, 139.2, 139.4 q (C³, J 34 Hz), 140.1 q (C², J 5.0Hz), 148.6. ¹⁹F {¹H} NMR (CDCl₃, 376 MHz) δ, ppm: −64.04 s (CF₃). HRMS (MALDI): C₁₉H₁₈F₃O₂ found 335.1253 [M + H]⁺, calcd 335.1267.

3-(Trifluoromethyl)-5,6-dimethyl-1-phenyl-1H-indene (3j1), and 3-(trifluoromethyl)-6,7-dimethyl-1-phenyl-1H-indene (3j2). Yield 96%. Colorless solid. M.p. 85–88 °C (for ratio of 3j1 : 3j2 1.25 : 1). Compound 3j1: ¹H NMR (CDCl₃, 400 MHz) (from the spectrum of a mixture of isomers) δ, ppm: 2.26 s (3H, Me), 2.34 s (3H, Me), 4.67 m (1H, C¹H), 6.93 m (1H, =CH), 7.08 c (1H_arom.), 7.10–7.12 m (2H_arom., J 1.5 Hz), 7.22 d (1H_arom., J 7.7 Hz), 7.24–7.31 m (3H_arom.). ¹³C NMR (CDCl₃, 100 MHz) (from the spectrum of a mixture of isomers, some signals) δ, ppm: 20.1 (Me), 20.2 (Me), 55.2 (C¹), 122.64 q (CF₃, J 270.0 Hz), 134.5 q (C³, J 34.1 Hz), 140.1 q (C², J 5.1 Hz). ¹⁹F {¹H} NMR (CDCl₃, 376 MHz) (from the spectrum of a mixture of isomers) δ, ppm: −64.00 s (CF₃) Mass spectrum (GC-MS), m/z (I_otH., %): 288 [M]⁺ (100). Compound 3j2: ¹H NMR (CDCl₃, 400 MHz) (from the spectrum of a mixture of isomers) δ, ppm: 1.99 c (3H, Me), 2.30 c (3H, Me), 4.72 m (1H, C¹H), 6.86 m (1H, =CH), 7.03–7.05 m (2H_arom.), 7.24–7.31 m (4H_arom.), 7.34 c (1H_arom.). ¹³C NMR (CDCl₃, 100 MHz) (from the spectrum of a mixture of isomers) δ, ppm: 15.8 (Me), 19.8 (Me), 55.4 (C¹), 122.62 q (CF₃, J 270.0 Hz), 133.4 q (C³, J 34.1 Hz), 140.9 q (C², J 5.1 Hz). ¹⁹F {¹H} NMR (CDCl₃, 376 MHz) (from the spectrum of a mixture of isomers) δ, ppm: −64.10 s (CF₃). For a mixture of isomers: 7.24–7.31 m (3H_arom.^A + 4H_arom.^B). Mass spectrum (GC-MS), m/z (I_otH., %): 288 [M]⁺ (80). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 118.1, 121.9, 125.7, 127.3, 127.5, 128.0, 129.1, 129.5, 133.4, 135.6, 135.8, 135.9, 136.1, 136.7, 136.8, 137.7, 145.9, 146.1. HRMS (MALDI): C₁₈H₁₆F₃ found 289.1199 [M + H]⁺, calcd 289.1204 (for a mixture of isomers).

3-(Trifluoromethyl)-4,6-dimethyl-1-phenyl-1H-indene (3k). Yield 97%. Yellow solid. M.p. 111–113 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.35 c (3H, Me), 2.59 c (3H, Me), 4.64 m (1H, C¹H), 7.00 c (1H_arom.), 7.03 c (1H_arom.), 7.09 m (1H, =CH), 7.15 d (2H_arom., J 6.6 Hz), 7.30–7.37 m (3H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 20.0 q (Me, J 4.7 Hz), 21.2 (Me), 54.6 (C¹), 122.9 q (CF₃, J 269.4 Hz), 123.1, 127.5, 128.1, 129.1, 131.3, 131.4, 133.8, 134.5 q (C³, J 33.9 Hz), 137.0, 137.8, 141.8 q (C², J 6.3 Hz), 149.8. ¹⁹F {¹H} NMR (CDCl₃, 376 MHz) δ, ppm: −60.61 s (CF₃). HRMS (MALDI): C₁₈H₁₆F₃ found 289.1199 [M + H]⁺, calcd 289.1214.

3-(Trifluoromethyl)-4,7-dimethyl-1-phenyl-1H-indene (3l). Yield 97%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.01 c (3H, Me), 2.55 c (3H, Me), 4.64 m (1H, C¹H), 6.98 d (1H_arom., J 7.7 Hz), 7.02–7.05 m (=CH + 2H_arom.), 7.12 d (1H_arom., J 7.7 Hz), 7.23–7.30 m (3H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 18.7 (Me), 19.8 q (Me, J 4.8 Hz), 54.5 (C¹), 122.9 q (CF₃, J 269.4 Hz), 127.3, 128.1, 128.6, 129.0, 129.2, 131.1, 131.9, 133.5 q (C³, J 33.9 Hz), 136.3, 137.0, 143.7 q (C², J 6.4 Hz), 146.9. ¹⁹F {¹H} NMR (CDCl₃, 376 MHz) δ, ppm: −60.50 s (CF₃). HRMS (MALDI): C₁₈H₁₆F₃ found 289.1199 [M + H]⁺, calcd 289.1208.

3-(Trifluoromethyl)-4,6,7-trimethyl-1-phenyl-1H-indene (3m). Yield 97%. Yellow solid. M.p. 59–61 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 1.94 c (3H, Me), 2.26 c (3H, Me), 2.51 c (3H, Me), 4.65 m (1H, C¹H), 6.96 c (1H_arom.), 7.02–7.03 m (=CH + 2H_arom.), 7.21–7.29 m (3H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 15.5 (Me), 19.5 (Me), 19.7 q (Me, J 4.8 Hz), 54.6 (C¹), 122.9 q (CF₃, J 269.4 Hz), 126.9, 127.2, 128.0, 128.6, 129.0, 132.7, 133.2 q (C³, J 33.8 Hz), 134.9, 135.7, 137.1, 142.8 q (C², J 6.4 Hz), 147.2. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −60.69 d (CF₃, J 1.8 Hz). HRMS (MALDI): C₁₉H₁₈F₃ found 303.1355 [M + H]⁺, calcd 303.1361.

3-(Trifluoromethyl)-1-(3,4-methylenedioxyphenyl)-1H-indene (3n). Yield 91%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 4.65 m (1H, C¹H), 5.92 m (2H, AB system, CH₂), 6.45 d (1H_arom., J 1.7 Hz), 6.67 dd (1H_arom., J 7.9 Hz, J 1.7 Hz), 6.76 d (1H_arom., J 7.9 Hz), 6.97 m (1H, =CH), 7.27–7.31 m (2H_arom.), 7.36 dt (1H_arom., J 7.2 Hz, J 1.8 Hz), 7.53 dd (1H_arom., J 7.5 Hz, J 0.8 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 55.2 (C¹), 101.3, 108.0, 108.7, 121.0, 121.4, 122.5 q (CF₃, J 270.0 Hz), 124.5, 127.0, 127.5, 134.5 q (C³, J 34.2 Hz), 138.1, 141.1 q (C², J 5.0 Hz), 147.1, 148.1, 148.2. ¹⁹F {1H} NMR (CDCl₃, 376 MHz) δ, ppm: −64.07 s (CF₃). HRMS (MALDI): C₁₇H₁₂F₃O₂ found 305.0784 [M + H]⁺, calcd 305.0792.

1-(4-Chlorophenyl)-3-(trifluoromethyl)-1H-indene (3o). Yield 97%. Yellow solid. M.p. 53–55 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 4.71 m (1H, C¹H), 7.00 m (1H, =CH), 7.05 d (2H_arom., J 7.7 Hz), 7.28–7.30 m (4H_arom.), 7.37–7.43 m (1H_arom.), 7.59 d (1H_arom., J 6.9 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 54.9 (C¹), 121.1, 122.4 q (CF₃, J 270.0 Hz), 124.5, 127.2, 127.7, 129.3, 129.4, 133.5, 135.0 q (C³, J 34.4 Hz), 135.6, 138.1, 140.5 q (C², J 4.9 Hz), 147.6. ¹⁹F {1H} NMR (CDCl₃, 376 MHz) δ, ppm: −64.04 s (CF₃). HRMS (MALDI): C₁₆H₁₁F₃³⁵Cl found 295.0496 [M + H]⁺, calcd 295.0503.

6-Fluoro-3-(trifluoromethyl)-1-(3,4-dimethylphenyl)-1H-indene (3p). Yield 97%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.23 s (3H, Me), 2.25 s (3H, Me), 4.65 m (1H, C¹H), 6.83–6.85 m (2H_arom.), 6.97–6.98 m (1H_arom., C²H), 7.02 dd (1H_arom., ³J_H–F 8.8 Hz, ⁴J 2.3 Hz), 7.04–7.10 m (2H_arom.), 7.47 dd (1H_arom., J 7.8 Hz, ⁴J_H–F 5.0 Hz).¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 19.5 (Me), 19.9 (Me), 55.3 d (C¹, J_C–F 2.3 Hz), 112.4 d (J_C–F 23.5 Hz), 114.5 d (J_C–F 23.5 Hz), 121.8 d (J_C–F 8.3 Hz), 122.4 q (CF₃, J_C–F 269.9 Hz), 125.4, 129.0, 130.4, 133.4, 133.7 q (C³, J_C–F 34.5 Hz), 134.1 q (J_C–F 1.1 Hz), 136.3, 137.6, 141.1 quintet (C⁴, J_C–F 4.9 Hz), 150.9 d (J_C–F 8.3 Hz), 162.6 d (C⁶, J_C–F 246.4 Hz). ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −114.91 td (F, ³J_H–F 8.8 Hz, ⁴J_H–F 5.0 Hz), −64.14 s (CF₃). HRMS (MALDI): C₁₈H₁₅F₄ found 307.1104 [M + H]⁺, calcd 307.1089.

6-Fluoro-3-(trifluoromethyl)-1-(3,4-dimethoxyphenyl)-1H-indene (3q). Yield 74%. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 3.81 s (3H, OMe), 3.86 s (3H, OMe), 4.64 m (1H, C¹H), 6.51 d (1H_arom., ⁴J 2.0 Hz), 6.69 dd (1H_arom., ³J 8.2 Hz, ⁴J 2.0 Hz), 6.81 d (1H, C²H, ³J 8.2 Hz), 6.97–6.99 m (1H_arom., C²H), 7.01 dd (1H_arom., ³J_H–F 8.8 Hz, ⁴J 2.2 Hz), 7.06 td (1H_arom., ³J_H–F 8.8 Hz, ⁴J 2.2 Hz), 7.47 dd (1H_arom., ³J 7.7 Hz, ⁴J_H–F 4.9 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 55.3 d (C¹, J_C–F 2.4 Hz), 56.1 (2MeO), 110.9, 111.8, 112.3 d (J_C–F 23.5 Hz), 114.7 d (J_C–F 23.5 Hz), 120.3, 121.9 d (J_C–F 8.8 Hz), 122.4 q (CF₃, J_C–F 269.9 Hz), 128.6.4, 133.7 q (C³, J_C–F 34.6 Hz), 133.9, 140.9 quintet (C⁴, J_C–F 4.9 Hz), 148.9, 149.6, 150.5 d (J_C–F 8.3 Hz), 162.6 d (C⁶, J_C–F 246.6 Hz).¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −114.72 td (F, ³J_H–F 8.8 Hz, ⁴J_H–F 4.9 Hz), −64.15 s (CF₃). HRMS (MALDI): C₁₈H₁₅F₄O₂ found 339.1003 [M + H]⁺, calcd 339.1018.

Synthesis and characterization of indenes 4

General procedure for isomerization of indenes 3 into 4. A suspension of 4 g of silica gel in a solution of 0.1 mmol of indene 3 in 5 mL of EtOAc was stirred at room temperature for 4 h. The silica gel was filtered off, and washed with EtOAc (3 × 20 mL). The solutions in EtOAc were combined, and evaporation of the solvent under reduced pressure quantitatively gave indene 4.

1-(Trifluoromethyl)-3-phenyl-1H-indene (4a). Quantitative yield. Yellow solid. M.p. 50–52 °C (lit.¹³ m.p. 49–51 °C). ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 4.24 qd (1H, C¹H, J 9.4 Hz, J 2.0 Hz), 6.41 d (1H, =CH, J 2.0 Hz), 7.32 t (1H_arom., J 7.5 Hz), 7.40–7.50 m (4H_arom.), 7.55–7.62 m (3H_arom.), 7.65 d (1H_arom., J 7.5 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 52.7 q (C¹, J 29.4 Hz), 121.3, 124.8 q (C², J 2.7 Hz), 124.9, 126.3 q (CF₃, J 278.5 Hz), 126.4, 127.8, 128.5, 128.8, 129.5, 134.6, 138.8, 144.2, 149.4. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −67.35 dd (CF₃, J 9.3 Hz, J 0.7 Hz). HRMS (MALDI): C₁₆H₁₂F₃ found 261.0886 [M + H]⁺, calcd 261.0885.

1-(Trifluoromethyl)-3-(4-methylphenyl)-1H-indene (4c). Quantitative yield. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.44 c (3H, Me), 4.24 qd (1H, C¹H, J 9.3 Hz, J 2.0 Hz), 6.40 d (1H, =CH, J 2.0 Hz), 7.30 d (2H_arom., J 7.9 Hz), 7.34 t (1H_arom., J 7.5 Hz), 7.43 t (1H_arom., J 7.5 Hz), 7.52 d (2H_arom., J 7.9 Hz), 7.58 d (1H_arom., J 7.5 Hz), 7.68 d (1H_arom., J 7.5 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 21.6 (Me), 52.7 q (C¹, J 29.5 Hz), 121.3, 124.2 q (C², J 2.7 Hz), 124.9, 126.3 q (CF₃, J 278.5 Hz), 126.4, 127.7, 128.5, 129.5, 131.8, 138.5, 138.9 q (J 1.6 Hz), 144.4, 149.3. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −67.31 d (CF₃, J 9.3 Hz). HRMS (MALDI): C₁₇H₁₄F₃ found 275.1042 [M + H]⁺, calcd 275.1047.

1-(Trifluoromethyl)-5-methyl-3-(4-methylphenyl)-1H-indene (4d). Quantitative yield. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.43 c (3H, Me), 2.44 c (3H, Me), 4.21 br. q (1H, C¹H, J 9.2 Hz), 6.38 d (1H, =CH, J 2.1 Hz), 7.16 d (1H_arom., J 7.6 Hz), 7.30 d (2H_arom., J 7.9 Hz), 7.38 s (2H_arom.), 7.51 d (2H_arom., J 7.9 Hz), 7.55 d (1H_arom., J 7.6 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 21.4 (Me), 21.8 (Me), 52.4 (C¹, J 29.4 Hz), 122.1, 124.5 q (C², J 2.8 Hz), 124.6, 126.4 q (CF₃, J 278.4 Hz), 127.1, 127.8, 129.5, 131.9, 136.0 q (J 1.8 Hz), 138.4, 138.5, 144.6, 149.3. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −67.49 d (CF₃, J 9.4 Hz). HRMS (MALDI): C₁₈H₁₆F₃ found 289.1199 [M + H]⁺, calcd 289.1209.

1-(Trifluoromethyl)-5-methoxy-3-phenyl-1H-indene (4e). Quantitative yield. Yellow solid. M.p. 77–79 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 3.87 c (3H, OMe), 4.23 qd (1H, C¹H, J 9.3 Hz, J 2.1 Hz), 6.35 d (1H, =CH, J 2.1 Hz), 7.01 d (2H_arom., J 8.8 Hz), 7.33 dt (1H_arom., J 7.4 Hz, J 0.9 Hz), 7.42 t (1H_arom., J 7.4 Hz), 7.54–7.58 m (3H_arom.), 7.66 d (1H_arom., J 7.4 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 52.7 q (C¹, J 29.4 Hz), 55.5 (OMe), 114.3, 121.3, 123.7 q (C², J 2.8 Hz), 124.9, 126.3 q (CF₃, J 278.5 Hz), 127.2, 128.5, 129.1, 138.9, 144.5, 148.9, 160.0. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −67.34 d (CF₃, J 9.5 Hz). HRMS (MALDI): C₁₇H₁₄F₃O found 291.0991 [M + H]⁺, calcd 291.0990.

1-(Trifluoromethyl)-5,6-dimethoxy-3-phenyl-1H-indene (4g). Quantitative yield. Yellow solid. M.p. 86–88 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 3.89 c (3H, OMe), 3.95 c (3H, OMe), 4.18 br. q (1H, C¹H, J 9.3 Hz), 6.32 d (1H, =CH, J 1.9), 7.07 c (1H_arom.), 7.22 c (1H_arom.), 7.43 t (1H_arom., J 7.3 Hz), 7.49 t (2H_arom., J 7.3 Hz), 7.59 d (2H_arom., J 7.3 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 52.5 q (C¹, J 29.4 Hz), 56.3 (OMe), 56.5 (OMe), 104.9, 108.8, 123.5 q (C², J 2.8 Hz), 126.3 q (CF₃, J 278.5 Hz), 127.7, 128.6, 128.9, 131.3, 135.0, 137.3, 148.4, 149.2, 149.8. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −67.58 d (CF₃, J 9.3 Hz). HRMS (MALDI): C₁₈H₁₆F₃O₂ found 321.1097 [M + H]⁺, calcd 321.1097.

1-(Trifluoromethyl)-5-methyl-3-(3,4-dimethoxyphenyl)-1H-indene (4i). Quantitative yield. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.42 (3H, Me), 3.95 (3H, OMe), 3.95 (3H, OMe), 4.20 qd (1H, C¹H, J 9.3 Hz, J 1.9 Hz), 6.35 d (1H, =CH, J 1.9 Hz), 6.98 d (1H_arom., J 8.2 Hz), 7.09 d (1H_arom., J 1.9 Hz), 7.14–7.19 m (2H_arom.), 7.38 c (1H_arom.), 7.54 d (1H_arom., J 7.6 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 21.8 (Me), 52.3 q (C¹, J 29.5 Hz), 56.1 (OMe), 56.2 (OMe), 111.2, 111.4, 120.4, 122.0, 124.2 q (C², J 2.7 Hz), 124.6, 126.3 q (CF₃, J 278.4 Hz), 127.2, 127.6, 136.0 d (J 1.9 Hz), 138.5, 144.6, 149.1, 149.3 149.5. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −67.48 d (CF₃, J 9.3 Hz). HRMS (MALDI): C₁₉H₁₈F₃O₂ found 335.1253 [M + H]⁺, calcd 335.1258.

1-(Trifluoromethyl)-5,6-dimethyl-3-phenyl-1H-indene (4j1). 4j1 was obtained as a mixture with 3j2. Quantitative yield. A yellow oily mixture of isomers. Compound 4j1: ¹H NMR (CDCl₃, 400 MHz) (from the spectrum of a mixture of isomers) δ, ppm: 2.32 c (3H, Me), 2.35 c (3H, Me), 4.19 qd (1H, C¹H, J 9.0 Hz, J 2.0 Hz), 6.33 d (1H, =CH, J 2.0 Hz), 7.27–7.31 m (1H_arom.), 7.40–7.50 m (4H_arom.), 7.60 d (2H_arom., J 8.4 Hz). ¹³C NMR (CDCl₃, 100 MHz) (from the spectrum of a mixture of isomers, some signals) δ, ppm: 20.1 (Me), 20.3 (Me), 55.4 q (C¹, J 29.4 Hz), 124.0 q (C², J 2.6 Hz), 126.4 q (CF₃, J 278.5 Hz). ¹⁹F NMR (CDCl₃, 376 MHz) (from the spectrum of a mixture of isomers) δ, ppm: −67.45 d (CF₃, J 9.0 Hz). Mass spectrum (GC-MS), m/z (I_otH., %): 288 [M]⁺ (100). HRMS (MALDI): C₁₈H₁₆F₃ found 289.1199 [M + H]⁺, calcd 289.1202 (for a mixture of isomers).

1-(Trifluoromethyl)-5,7-dimethyl-3-phenyl-1H-indene (4k). Quantitative yield. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.37 c (3H, Me), 2.46 c (3H, Me), 4.25 qd (1H, C¹H, J 8.1 Hz, J 2.1 Hz), 6.39 d (1H, =CH, J 2.1 Hz), 6.98 c (1H_arom.), 7.18 c (1H_arom.), 7.41–7.50 m (3H_arom.), 7.57–7.59 m (2H_arom.). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 20.0 q (Me, J 3.7 Hz), 21.5 (Me), 52.0 q (C¹, J 29.2 Hz), 119.9, 125.9 q (C², J 3.1 Hz), 126.7 q (CF₃, J 279.9 Hz), 128.0, 128.5, 128.8, 129.7, 134.2, 135.0, 135.2, 138.7, 145.3, 149.4. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −63.90 dd (CF₃, J 8.2 Hz, J 1.3 Hz). HRMS (MALDI): C₁₈H₁₆F₃ found 289.1199 [M + H]⁺, calcd 289.1207.

3-(4-Chlorophenyl)-1-(trifluoromethyl)-1H-indene (4o). Quantitative yield. Yellow solid. M.p. 49–51 °C. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 4.25 qd (1H, C¹H, J 9.3 Hz, J 2.1 Hz), 6.43 d (1H, =CH, J 2.1 Hz), 7.35 dt (1H_arom., J 7.4 Hz, J 0.9 Hz), 7.41–7.46 m (3H_arom.), 7.50–7.55 m (3H_arom.), 7.67 d (1H_arom., J 7.4 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 52.8 q (C¹, J 29.6 Hz), 121.1, 125.1, 125.2 q (C², J 2.8 Hz), 126.1 q (CF₃, J 278.6 Hz), 126.7, 128.7, 129.1, 129.2, 133.1, 134.6, 138.7, 143.9, 148.4. ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −67.23 d (CF₃, J 9.3 Hz). HRMS (MALDI): C₁₆H₁₁F₃Cl found 295.0496 [M + H]⁺, calcd 295.0496.

5-Fluoro-1-(trifluoromethyl)-3-(3,4-dimethylphenyl)-1H-indene (4p). Quantitative yield. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 2.36 (3H, Me), 2.37 (3H, Me), 4.22 br. q (1H, C¹H, J 9.1 Hz), 6.47 c (1H, =CH), 7.03 dt (1H_arom., J 8.5 Hz, J 2.2 Hz), 7.25–7.35 m (3H_arom.), 7.37 c (1H_arom.), 7.60 dd (1H_arom., J 7.7 Hz, J 5.4 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 19.7 (Me), 20.0 (Me), 52.2 q (C¹, J 29.7 Hz), 109.0 d (J 24.2 Hz), 113.0 d (J 23.2 Hz), 125.1, 125.8 d (J 9.3 Hz), 126.0 q (C², J 2.6 Hz), 126.1 q (CF₃, J 278.5 Hz), 128.9, 130.2, 131.6, 134.2 m, 137.4 d (J 25.7 Hz), 146.8 d (J 9.0 Hz), 148.8 d (J 2.9 Hz), 163.6 d (J 245.3 Hz). ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −113.55 to −113.48 m (1F_arom.), −67.52 d (CF₃, J 9.1 Hz). HRMS (MALDI): C₁₈H₁₅F₄ found 307.1104 [M + H]⁺, calcd 307.1107.

5-Fluoro-1-(trifluoromethyl)-3-(3,4-dimethoxyphenyl)-1H-indene (4q). Quantitative yield. Yellow oil. ¹H NMR (CDCl₃, 400 MHz) δ, ppm: 3.94 (6H, 2OMe), 4.21 br. q (1H, C¹H, J 8.9 Hz), 6.44 d (1H, =CH, J 2.1 Hz), 6.97 d (1H_arom., J 8.2 Hz), 7.02 dt (1H_arom., J 8.7 Hz, J 2.4 Hz), 7.06 d (1H_arom., J 1.9 Hz), 7.14 dd (1H_arom., J 8.2 Hz, J 1.9 Hz), 7.26 dd (1H_arom., J 9.0 Hz, J 2.4 Hz), 7.58 dd (H_arom., J 8.0 Hz, J 5.1 Hz). ¹³C NMR (CDCl₃, 100 MHz) δ, ppm: 52.2 q (C¹, J 29.8 Hz), 56.1 (OMe), 56.2 (OMe), 108.9 d (J 24.3 Hz), 110.9, 111.5, 113.1 d (J 23.2 Hz), 120.3, 125.8 q (C², J 2.6 Hz), 125.9 d (J 9.2 Hz), 126.0 q (CF₃, J 278.5 Hz), 126.8, 134.1 m, 146.7 d (J 8.8 Hz), 148.5 d (J 2.9 Hz), 149.6 d (J 44.1 Hz), 163.6 d (J 245.5 Hz). ¹⁹F NMR (CDCl₃, 376 MHz) δ, ppm: −113.31 dt (1F_arom., J 9.0 Hz, J 5.1 Hz), −67.51 d (CF₃, J 8.9 Hz). HRMS (MALDI): C₁₈H₁₅F₄O₂ found 339.1003 [M + H]⁺, calcd 339.1009.

Acknowledgements

This work was supported by the Russian Scientific Foundation (grant no. 14-13-00448). Spectral studies were performed at the Center for Magnetic Resonance, and the Center for Chemical Analysis and Materials Research of Saint Petersburg State University, Saint Petersburg, Russia.

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Footnote

† Electronic supplementary information (ESI) available: ¹H, ¹³C, ¹⁹F NMR spectra of compounds, and data on DFT calculations. See DOI: 10.1039/c7ob00406k

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