An unprecedented deoxygenation protocol of benzylic alcohols using bis(1-benzotriazolyl)methanethione

Abstract

A facile and regioselective two-step protocol for the deoxygenation of benzylic alcohols using bis(benzotriazole)methanethione has been devised. Benzotriazole derivatives, namely, benzyloxythioacylbenzotriazoles (ROCSBt), on reaction with silanes or Bu₃SnH under microwave irradiation or conventional heating undergo a free radical β-scission of C–O bond instead of N–N bond (benzotriazole ring cleavage) to afford a deoxy product. The methodology has various applications because it selectively deoxygenates benzylic alcohols with the aid of a relatively nontoxic (TMS)₃SiH reagent as an acceptable alternate to Bu₃SnH.

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Introduction

The advantages associated with utilizing benzotriazole as a synthetic auxiliary for common organic transformations lie in enabling them to be rather efficient, fast, and inexpensive.¹ Deoxygenation plays an important role in numerous synthetic transformations. Some common methods include well-known Barton–McCombie deoxygenation,² Marko–Lam de-oxygenation,³ Wolff–Kishner reduction,⁴ opening of epoxide ring via addition to unsaturated compounds⁵ or by the hydride reduction of corresponding mesylates or tosylates.⁶ The replacement of an allylic or a benzylic hydroxyl group through hydride displacement is sometimes complicated because the activation of the hydroxyl function into a suitable leaving group is difficult. The most commonly used activated derivatives, viz., chlorides, bromides and arylsulfonates, may be reactive to such an extent that it is difficult to obtain the product with satisfactory purity, and they cannot be stored for a long period of time. Corey et al. used a pyridine–sulfurtrioxide complex with LiAlH₄ in THF for the activation of hydroxyl groups;⁷ however, the harsh reduction condition limited its scope towards a wide range of substrates. A report by Kim et al. on the selective deoxygenation of alkoxyalkyl ether (EE or MOM) of allylic alcohols by Pd(dppe) Cl₂-catalyzed reduction with LiBHEt₃ is well documented.⁸ However, the involvement of a three-step reaction sequence to obtain only moderate yields and the use of expensive and carcinogenic Pd-catalyst limits the wide applicability of this method.

In classical Barton–McCombie deoxygenation, a thiocarbonyl moiety is commonly present that can be readily desulfurized in a fairly mild reaction condition. Deoxygenation via bis(benzotriazole)methanethione, 2, has several important features: their preparation from the readily available benzotriazole is an easy process and the benzotriazole derived thiocarbamate intermediate has a long term stability; moreover, these compounds can incorporate a relatively more weaker benzylic C–O bond rather than a benzotriazolyl N–N bond at the beta (β) position to the thiocarbonyl moiety, which could be possibly cleaved similar to that observed in Barton–McCombie deoxygenation (Fig. 1). In addition, the abovementioned radical deoxygenation is rather efficient under microwave conditions.

Fig. 1 Barton–McCombie deoxygenation and cyclization via benzotriazole ring cleavage.

Recently, to widen the approach of our ongoing study on benzotriazole methodology,⁹ we reported the synthesis of 2-N/S/C/O-substituted benzothiazoles via the cyclic-cleavage of benzotriazole ring using silane or stannane reagents.^9j,k However, the phenomenon appears to be unusual in the case of benzylic alcohols, which under similar reaction condition undergo unparalleled deoxygenation instead of cyclization, which has been reported herein.

Results and discussion

Our investigation begins with the thioacylation of benzylic alcohols using a benzotriazole based reagent, 2, to afford the corresponding benzyloxythioacylbenzotriazoles (ROCSBt),^9,10 which on further treatment with silanes or stannanes under conventional heating or microwave (MW) condition give deoxy products with moderate to good yields (Scheme 1c). The case is different with aliphatic alcohols, which under similar reaction condition undergo cyclization to afford good to excellent yields of 2-(alkoxy)benzothiazoles via the free radical intramolecular cyclic-cleavage of N–N bond of benzotriazole ring (Scheme 1a).⁹ However, 2,3:5,6-di-O-isopropylidene mannose on reaction with 2 in the presence of Et₃N and pyridine in anhydrous CH₂Cl₂ affords 2-N-benzotriazole-2′,3′:5′,6′-di-O-isopropylidene-β-D-mannofuranoside (Scheme 1b).¹¹ Thus, the three alcohols, viz., benzylic, aliphatic and anomeric, give different results under the similar condition.

Scheme 1 Comparative illustration of previous and present work.

The deoxy product 12, a carbohydrate derivative, has been synthesized from benzylic alcohol 10 (ref. 12) by the radical deoxygenation of intermediate 11. The treatment of compound 10 with bis(benzotriazole)methanethione, 2, in the presence of Et₃N (0.3 equiv.) in anhydrous CH₂Cl₂ at room temperature furnished compound 11, which was further treated with the reagent that is capable of free radical induction in dry toluene to afford compound 12 in a good yield (Scheme 2).

Scheme 2 Synthesis of compound 12 using compound 2.

Compound 11 was characterized by its characteristic NMR signals. A peak corresponding to benzotriazolyl protons in ¹H NMR appears in the aromatic region; moreover, a characteristic peak of thiocarbonyl carbon appears at δ 167.7 ppm in ¹³C NMR spectrum of 11 (see ESI†). The compound 12 was characterized by the disappearance of signals that correspond to benzotriazolyl proton in its ¹H NMR spectra; in addition, the disappearance of the characteristic peak of thiocarbonyl carbon and the appearance of a methylene carbon signal at δ 47.2 ppm in ¹³C NMR suggest the formation of compound 12 (see ESI file†). In addition, the mass spectrum of compound 12 exhibited an [M + H]⁺ peak at m/z 391, which was 177 units less than the molecular ion peak, [M + H]⁺, of compound 11 observed at m/z 568. Together with NMR, mass and elemental data also suggest that deoxygenation would occur in this condition rather than the well-known cyclization.

For the aforementioned deoxygenation, we briefly investigated the effect of the diverse range of silanes in terms of yield and reaction time; the results obtained have been summarized in Table 1. The obtained results clearly demonstrate that reagent feasibility depends solely on the Si–H and Sn–H bond strength among silanes and stannanes. The deoxygenation carried out in the presence of triethylsilane (Et₃SiH), tris(iso-propyl)silane (Prⁱ₃SiH) and diphenylsilane (Ph₂SiH₂) resulted in poor yields. Compared to 1,2-dimethyl-1,2-diphenyldisilane (Ph(CH₃)SiH)₂, 1,1,2,2-tetraphenyldisilane ((Ph)₄Si₂H₂) performed better. The deoxygenation with tris(trimethylsilyl)silane (TMS)₃SiH and (Ph)₄Si₂H₂ is comparatively better; however, the higher yield of compound 12 was noticed with n-Bu₃SnH. For deoxygenation carried out with alkyl-, phenyl- or trimethylsilyl-substituted silanes and disilanes, the yield of compound 12 increased persistently with phenyl or trimethylsilyl substitution. Chatgilialoglu et al. described the use of (TMS)₃SiH as a substitute to Bu₃SnH under moderate conditions.¹³ In comparison to n-Bu₃SnH, the trialkylsilyls are more reactive towards addition to multiple bonds¹⁴ and abstraction of halogen;¹⁵ however, they are rather poor H-atom donors toward alkyl radicals, and therefore support chain reactions only at elevated temperatures. Moreover, the greater strength of the Si–H bond (78 kcal mol⁻¹) in (TMS)₃SiH compared to Sn–H bond (74 kcal mol⁻¹) in n-Bu₃SnH results in relatively slow deoxygenation with silanes and requires considerably high temperatures or addition of initiators.¹⁶

Table 1 Optimization^a of the radical conversion of compound 11 to 12 using 2.2 molar equivalents of reagents

Entry	Reagent^b	Initiator^c (mol%)	Temp^d (°C)	Yield^e % (time)	Yield^f % (time)
a All the reactions are carried out under microwave conditions at 110 °C.b Reagents are arranged on the basis of increasing order of yield.c AIBN is used as the radical initiator.d Reaction temperature is 80–150 °C.e Isolated yield and reaction time are presented in hours under conventional heating.f Isolated yield obtained for reactions under microwave exposure for 30 min.
1	Et3SiH	5	80	Trace (12)	Trace
2	Et3SiH	0	150	Trace (12)	Trace
3	Pr^i3SiH	5	80	Trace (12)	Trace
4	Pr^i3SiH	0	150	Trace (12)	Trace
5	Ph2SiH2	5	80	Trace (12)	Trace
6	Ph2SiH2	0	150	Trace (12)	Trace
7	Bu^tPh2SiH	5	80	40 (6)	44
8	Bu^tPh2SiH	0	150	42 (12)	47
9	(Ph(CH3)SiH)2	5	80	48 (6)	54
10	(Ph(CH3)SiH)2	0	150	50 (12)	47
11	Ph3SiH	5	80	66 (6)	68
12	Ph3SiH	0	150	63 (12)	65
13	(TMS)3SiH	5	80	75 (6)	74
14	(TMS)3SiH	0	150	73 (12)	69
15	(Ph)4Si2H2	5	80	78 (6)	76
16	(Ph)4Si2H2	0	150	65 (12)	71
17	Bu3SnH	5	80	83 (6)	85
18	Bu3SnH	0	80	73 (12)	74

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The factors that moderate Si–H bond dissociation enthalpies are not yet completely understood; however, the available thermo-chemical data on Si–H bond dissociation energies¹⁷ and the rate constant for the reaction of some radicals with a variety of silicon hydrides suggest that the bond-weakening effects are operative on trimethylsilyl or phenyl substitution due to radical stabilization by the π-conjugation of phenyl group(s) and the d-orbital participation of trimethylsilyl group.¹⁸ The high cost of disilane (Ph)₄Si₂H₂ limits its further exploration in our free radical deoxygenation, whereas the use of Bu₃SnH was ruled out for green perspectives.^18b,19 Moreover, it appeared inappropriate to utilize toxic Bu₃SnH as radical reducing agent for the synthesis of compounds that have value in medicine and agriculture.

Solvent effect was briefly investigated using various solvents in the presence of AIBN (5 mol%) and (TMS)₃SiH (2.2 molar equiv.) at 110 °C (Table 2). The results illustrated the poor performances of cyclohexane, n-hexane, benzene, toluene, 1,4-dioxane, dichloromethane and chloroform in terms of yield and reaction time. The higher yield observed with toluene was mainly due to its capacity to sustain higher temperatures, i.e., it has a higher boiling point compared to dichloromethane, chloroform, cyclohexane, n-hexane, and benzene.

Table 2 Solvent optimization for the conversion of 11 to 12 using (TMS)₃SiH (2.2 molar equiv.) in the presence of AIBN (5 mol%)

Entry	Solvent^a	Time (h)	Yield^b (%)
a 2.0 mL of solvent was used for 1 mmol of 11.b Reaction time 4–12 h.c Reaction was carried out in a sealed tube.
1	Cyclohexane	6	17
2	n-Hexane	6	14
3	Benzene	6	67
4	Toluene	6	85
5	1,4-Dioxane	8	80
6	Dichloromethane	12	<10^c
7	Chloroform	12	<10^c

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The deoxygenation product 19, which is a carbohydrate derivative, has been synthesized from diol 16; it could also be obtained from compound 13 (ref. 12c) by the acid hydrolysis and subsequent NaBH₄ reduction of aldehyde 15 generated by the periodate cleavage of diol 14 (Scheme 3). Along with compound 17, a small amount of compound 18 has also been isolated from the reaction mixture. It was interesting to find that when both benzylic and aliphatic hydroxyl groups are present together in the same molecule, the benzylic hydroxyl group selectively undergoes deoxygenation, while the other promotes cyclization under the same reaction condition.

Scheme 3 Synthesis of compound 19 using 2.

The alcohol 1-ferrocenylmethanol, 21, prepared from NaBH₄ reduction of ferrocene aldehyde, 20, would be further deoxygenated to methyl-ferrocene, 23, via intermediate benzotriazole derivative, 22, with 79% yield. The completion of reaction takes 5 hours under conventional heating, whereas under microwave conditions only 30 minutes are required (Scheme 4).

Scheme 4 Synthesis of methyl-ferrocene 23.

Furthermore, using our standardized reaction conditions, benzotriazolethiocarbamates, 25a–d, were deoxygenated to their corresponding deoxy analogs, 26a–d, (Scheme 5). The structural assignments of 25a–d and 26a–d were supported by ¹H and ¹³C NMR spectra, mass and elemental analyses.

Scheme 5 Deoxygenation of benzylic alcohols 24a–d to 26a–d. ^aYield under MW/yield under conventional heating.

The higher yield of compound 12 is noticeable among all the synthesized deoxygenation products. This may be due to the extra stabilization of the corresponding radical by the cyclopropyl substituent.^20a The optimum overlap between the p-orbital of cyclopropylmethyl radicals and the Walsh orbital^20b,c of the cyclopropyl group may provide extra stabilization; moreover, some reports show that the calculated value of the stabilization energy of a cyclopropylmethyl radical with an optimum conformation is 12 kJ mol⁻¹.^20d,e

An attempt to deoxygenate aromatic alcohol 4-methoxyphenols, 27, under our optimized reaction condition results in their cyclization to corresponding benzothiazole 29 through the formation of the intermediate 28 via a cyclic ring cleavage of benzotriazole (Scheme 6). The structure of compound 28 was assigned by single crystal X-ray analysis.

Scheme 6 Reaction of 4-methoxyphenol 27 with compound 2.

In another case, the reaction of 1-ferrocenylethanol, 30, with 2 in the presence of Et₃N in anhydrous dichloromethane afforded a mixture of regioisomer, namely, 1-ferrocenyl-1-(1N-benzotriazolyl)ethane, 31, and 1-ferrocenyl-1-(2N-benzotriazolyl)ethane, 32, instead of the desired benzotriazolemethanethione adduct, 30a, (Scheme 7). The structures of compounds 31 and 32 were assigned by single crystal X-ray analysis (Fig. 2).

Scheme 7 Reaction of 1-ferrocenylethanol 30 with compound 2.

Fig. 2 Single-crystal X-ray molecular structure of 31 and 32. The displacement thermal ellipsoids are drawn at 40%.

The chemistry described herein offers a novel route to access the benzotriazole derivatives of ferrocene using compound 2. The reaction proceeds through the Et₃N promoted nucleophilic addition of 1-ferrocenylethanol to compound 2 by the substitution of one of the benzotriazole moiety. However, the resulting adduct 30a decomposes to form products 31 and 32. The mechanism of formation of the two regioisomers is supposed to be S_N1, involving the formation of an intermediate carbocation 30b. The carbocation intermediate, 30b, was stabilized by three hyperconjugated hydrogens and charge dispersal through delocalization over the cyclopentyl ring of the ferrocene moiety, and the charge after being captured by a benzotriazole anion via N1 and N2 nucleophilic center afforded a mixture of two regioisomer, namely, 31 and 32, in the ratio of 60 : 40. The two regioisomers were separated by flash column chromatography. The configuration at the carbon C7 observed in the single crystal X-ray structures of compounds 31 and 32 is exclusively C7-(R) (Fig. 2). The crystallographic and instrumental data for the compounds 28, 31, and 32 has been summarized in Table 3 (see ESI† CIF file for details).

Table 3 Crystallographic refinement data^a for compounds 28, 31 and 32

Property	28	31	32
a For details see ESI file (CIF) enclosed with manuscript.
Mol. formula	C14H11N3O2S	C18H17FeN3	C18H17FeN3
Formula weight	285.33	331.20	331.20
Crystal system	Triclinic	Monoclinic	Monoclinic
Space group	P1̄	P121/n1	P1211
a (Å)	4.2311(7)	6.6888(7)	6.1853(6)
b (Å)	8.0019(16)	28.847(2)	30.023(3)
c (Å)	20.415(3)	8.3300(10)	8.4797(9)
β (°)	92.671(13)	104.396(11)	104.478(10)
V (Å^3)	676.2(2)	1556.8(3)	1524.7(3)
Z	2	4	4
Density (calc)	1.401	1.413	1.443
F(000)	280	688.0	688
M (mm^−1)	0.234	0.968	0.988
Crystal size [mm]	0.16 × 0.17 × 0.24	0.13 × 0.15 × 0.23	0.12 × 0.18 × 0.20
Temperature (K)	293	293	293
Radiation (MoKα)	0.71073	MoKα 0.71073	MoKα 0.71073
θ min-max [°]	3.31, 28.87	3.22, 29.13	3.40, 29.08
h, k, l	−5 : 5; −8 : 10; −26 : 22	−8 : 8; −18 : 39; −5 : 11	−8 : 7; −38 : 39; −9 : 11
Tot., uniq data, R(int)	5013, 3051, 0.0264	6934, 3558, 0.0425	6476, 4835, 0.0328
Obs. data [I > 2.0σ(I)]	1550	2076	3163
Nref, Npar	3580, 181	4193, 259	4835, 433
R1, wR2, S	0.0590, 0.1104, 1.019	0.0694, 0.1545, 1.097	0.0611, 0.1212, 1.046
Min-max resd. dens. [e Å^−3]	−0.205, 0.167	−0.288, 0.370	−0.349, 0.416
CCDC	978009	978010	978011

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The proposed free-radical catalytic cycle shows the application of the deoxygenation approach to a (TMS)₃SiH catalyzed variant of the Barton–McCombie deoxygenation reaction, which is outlined in Scheme 8.^2,9k,21 The radical reduction of a thionocarbonate by (TMS)₃SiH affords carbon oxide sulfide (COS), the desired alkane, and (TMS)₃Si–Bt.²²

Scheme 8 (TMS)₃SiH mediated radical deoxygenation.

Conclusions

The developed methodology is new, concise, efficacious and (TMS)₃SiH-mediated toxic metal-free approach for deoxygenation under mild conditions. Moreover, it is compatible under microwave conditions and gives a new method to avoid the use of highly toxic n-Bu₃SnH for radical deoxygenation. The methodology is extremely important in terms for green chemistry perspectives, and it is selective for benzylic alcohols. Thus, this approach should be of further interest to synthetic and medicinal chemists.

Experimental

General remarks

All the reactions were executed in anhydrous solvents under an Ar-atmosphere in oven dried glassware at 110 °C. All the reagents and solvents used were of analytical grade. Laboratory grade dichloromethane was first distilled and then further purified and dried by distillation from calcium hydride. Dry toluene and all the reagents were purchased from Sigma-Aldrich Chemical Company, Inc., with >99% purity and were used without further purification. 2,2′-Azobis(isobutyronitrile) (AIBN) (98%; Spectrochem Chemical Company, Inc.) was used without purification. Thin layer chromatography (TLC) was performed on silica gel 60 F₂₅₄, pre-coated on aluminum plates, which were analysed under either a UV lamp (λ_max = 254 nm) or by spraying with methanolic-H₂SO₄ solution and subsequent charring by heating at 100 °C. ¹H and ¹³C NMR spectra were recorded at 300 and 75 MHz, respectively. Chemical shifts are given in ppm downfield from internal TMS; J values are given in Hz. Mass spectra were recorded using electrospray ionization mass spectrometry (ESI-MS). Infrared spectra were recorded as Nujol mulls in KBr plates. Elemental analysis was performed using a C, H, and N analyzer, and results were found to be within ±0.4% of the calculated values. The reactions under microwave conditions were carried out in a single-mode microwave reactor.

The single-crystal X-ray data of compounds were collected on an Xcalibur Eos (Oxford) CCD-Diffractometer using graphite monochromated MoKα radiation (λ = 0.71073 Å). The data integration and reduction were processed with the CrysAlis Pro software.²³ The structures were solved by the direct method, and then refined on F² by the full matrix least-squares technique with the SHELX-97 set of software²⁴ using the WinGX (version 1.80.05) program package.²⁵ All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were treated as riding atoms using SHELX default parameters. Molecular structures have been drawn using the ORTEP software, as illustrated in Scheme 6 and Fig. 2. Further information on the crystal structure determination (excluding structure factors) has been given in Table 3.†

General procedure for the synthesis of benzyloxythioacyl benzotriazoles (11, 17, 22 and 25a–d)

A solution of alcohol 1 in anhydrous CH₂Cl₂, which was continuously stirred, was treated with bis(benzotriazolyl)methanethione, 2, in the presence of Et₃N under inert atmosphere. After the completion of the reaction (monitored by TLC), the reaction mixture was concentrated in vacuo. Extraction with CH₂Cl₂ and washing with 10% Na₂CO₃, water and brine solution was followed by drying over anhydrous Na₂SO₄, and then the organic layer was concentrated under reduced pressure. Further purification using flash column chromatography using ethyl acetate/n-hexane as an eluent afforded the respective pure benzotriazole methanethiones, namely, 11, 17, 22 and 25a–d.

General procedure for the MW-assisted deoxygenation

A solution of benzotriazolemethanethione 11, 17, 22 and 25a–d (1.0 mmol) in anhydrous toluene, which was continuously stirred, was treated with tris(trimethylsilyl)silane (2.2 equiv.) and AIBN (5 mol%) under inert atmosphere. The reaction mixture was stirred under heating at 110 °C, as well as exposed to single-mode microwave reactor with a new sealed pressure regulation 10 mL pressurized vial with ‘‘snap-on’’ cap and Teflon-coated magnetic stir bar. The standard temperature control system consisted of a non-contact calibrated infrared sensor, which monitored and controlled the temperature conditions of the reaction vessel located in the cavity of the instrument. For each reaction, the reaction temperature was 110 °C. After the completion of the reaction (monitored by TLC), the reaction mixture was concentrated in vacuo, extracted with CH₂Cl₂, washed with 10% LiOH, water and brine solutions. The organic layer was dried over anhydrous Na₂SO₄ followed by concentration in vacuo. Purification using flash column chromatography afforded the products, namely, 12, 19, 23, and 26a–d.

Physical data of the developed compounds

Bis(1H-benzo[d][1,2,3]triazol-1-yl)methanethione (2). Yellow crystals; IR (KBr) ν_max 1597, 1536, 1067, 1007, 959, 891, 728, 692, 650 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 8.27 (d, J = 8.4 Hz, 2H), 8.22 (d, J = 8.1 Hz, 2H), 7.74 (t, J = 7.8 Hz, 2H), 7.60 (t, J = 7.5 Hz, 2H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 169.6 (2C), 146.7 (2C), 133.0 (2C), 130.5 (2C), 126.9 (2C), 120.9 (2C), 113.8 (2C) ppm.

3′-O-(4-(Hydroxy)(cyclopropyl)methyl)-phenyl-1′,2′:5′,6′-di-O-isopropylidene-α-D-glucofuranose (10). Colorless solid; IR (KBr) ν_max 3641, 2983, 2942, 1616, 1589, 1105, 1087, 889, 764 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 7.37 (d, J = 8.4 Hz, 2H), 6.97 (d, J = 8.4 Hz, 2H), 5.92 (d, J = 3.3 Hz, 1H), 4.72 (s, 1H), 4.60 (d, J = 3.6 Hz, 1H), 4.48–4.46 (m, 1H), 4.33 (d, J = 7.8 Hz, 1H), 4.15–4.11 (m, 2H), 3.96 (d, J = 8.4 Hz, one isomer), 3.45 (d, J = 7.8 Hz, other isomer), 3.23 (s, 1H), 1.55, 1.43, 1.32 and 1.30 (each s, each 3H), 0.66–0.60 (m, 1H), 0.58–0.53 (m, 1H), 0.47–0.43 (m, 1H), 0.38–0.30 (m, 1H), 0.24–0.19 (m, 1H) ppm.

O-(Cyclopropyl(4-(1′,2′:5′,6′-di-O-isopropylidine-α-D-glucofuranoxy)phenyl)methyl)-1H-benzo[d][1,2,3]triazole-1-carbothioate (11). The compound 10 (0.406 g, 1.0 mmol) after treatment with 2 (0.31 g, 1.1 mmol) and Et₃N (0.3 equiv.) in dry CH₂Cl₂ (15 mL) was stirred for 8 h at room temperature. The crude product was purified by flash column chromatography (10% ethyl acetate/n-hexane) to afford a yellowish viscous liquid, 11, (0.436 g, 77%, R_f = 0.60, 20% ethyl acetate/n-hexane). IR (Nujol) ν_max 1744, 1616, 1579, 1088, 1067, 1054, 986, 974, 734 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 8.15 (d, J = 8.1 Hz, 1H), 8.10 (d, J = 8.4 Hz, 1H), 7.62 (t, J = 7.5 Hz, 1H), 7.50 (m, 1H), 7.46 (d, J = 8.7 Hz, 2H), 6.97 (d, J = 8.4 Hz, 2H), 5.90 (s, J = 3.6 Hz, 1H), 4.71 (d, J = 2.7 Hz, 1H), 4.59 (d, J = 3.6 Hz, 1H), 4.43 (dd, J = 6.0, 7.2 Hz, 1H), 4.31–4.25 (m, 2H), 4.13–4.08 (m, 2H), 1.54 (s, 3H), 1.42 (s, 3H), 1.29 (s, 6H), 0.78–0.70 (m, 2H), 0.68–0.56 (m, 1H), 0.50–0.43 (m, 1H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 167.6, 156.1, 146.1, 134.4, 130.7, 130.4, 129.1 (2C), 126.1, 120.2, 115.3 (2C), 113.6, 112.0, 109.1, 105.2, 82.0, 80.3, 79.7, 72.1, 66.9, 54.0, 26.7, 26.6, 26.1, 25.1, 16.9, 6.5, 6.2 ppm; MS: m/z 568 [M + H]⁺; anal. calcd for C₂₉H₃₃N₃O₇S: C, 61.36; H, 5.86; N, 7.40; found: C, 61.51; H, 5.98; N, 7.57.

3′-O-(4-(Cyclopropylmethyl)phenyl)-1′,2′,5′,6′-di-O-isopropylideneglucofuranose (12). Colorless viscous liquid; yield 85%; R_f = 0.68 (20% ethyl acetate/n-hexane); MS: m/z 391 [M + H]⁺; IR (Nujol) ν_max 2938, 1597, 1072, 1032, 981, 972, 875, 766, 732 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 7.26 (d, J = 8.4 Hz, 2H), 6.96 (d, J = 8.4 Hz, 2H), 5.93 (d, J = 3.3 Hz, 1H), 4.73 (d, J = 3.0 Hz, 1H), 4.62 (d, J = 3.9 Hz, 1H), 4.48 (dd, J = 12.3, 5.7 Hz, 1H), 4.33 (dd, J = 13.5, 3.0 Hz, 1H), 4.15–4.12 (m, 2H), 3.48 (d, J = 7.8 Hz, 2H), 2.72–2.55 (m, 1H), 1.55 (s, 3H), 1.44 (s, 3H), 1.32 (s, 3H), 1.31 (s, 3H), 1.17–1.09 (m, 1H), 0.68–0.60 (m, 1H), 0.48–0.43 (m, 2H), 0.26–0.18 (m, 1H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 156.1, 134.9, 128.0 (2C), 115.1 (2C), 111.9, 109.0, 105.1, 82.0, 80.3, 79.6, 72.1, 66.9, 47.2, 26.7, 26.6, 26.1, 25.1, 17.4, 4.2, 1.7 ppm.

3′-(4-((Cyclopropyl)hydroxymethyl)phenyl)-1′,2′-O-isopropylidene-α-D-xylofuranose (16). Viscous liquid; IR (Nujol) ν_max 3589, 2943, 1578, 1544, 1263, 1187, 979, 874, 763, 665 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 7.37 (d, J = 8.1 Hz, 2H), 6.93 (d, J = 7.8 Hz, 2H), 5.96 (s, 1H), 4.70 (s, 1H), 4.61 (m, 2H), 4.42–4.39 (m, 2H), 3.97 (d, J = 9.9 Hz, 1H), 2.18 (bs, 1H), 1.55 (s, 3H), 1.31 (s, 3H), 1.23 (m, 1H), 0.61–0.59 (m, 1H), 0.54 (m, 1H), 0.45 (m, 1H), 0.34 (m, 1H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 155.9, 137.4, 127.4 (2C), 114.9 (2C), 112.0, 105.1, 82.0, 80.2, 77.7, 77.6, 62.0, 26.6, 26.1, 19.0, 3.4, 2.6 ppm.

3′-O-(4-((Cyclopropyl)(1H-benzotriazolylmethanethionyl) methyl)phenyl)-1′,2′-O-isopropylidine-α-D-xylofuranose-5′-1H-benzotriazolecarbothioate (17). The compound 16 (0.672 g, 2.0 mmol) after treatment with 2 (1.193 g, 4.2 mmol) and Et₃N (0.4 equiv.) in anhydrous CH₂Cl₂ (20 mL) was stirred for 12 h at room temperature. The crude product was purified by flash column chromatography (10% ethyl acetate/n-hexane) to afford a light yellowish viscous liquid 17 (0.825 g, 63%, R_f = 0.70, 30% ethyl acetate/n-hexane). MS: m/z 659 [M + H]⁺; IR (Nujol) ν_max 1726, 1613, 1545, 1107, 1055, 1044, 876, 784, 637 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 8.33 (d, J = 7.8 Hz, 1H), 8.31–8.07 (m, 3H), 7.63–7.55 (m, 2H), 7.46–7.44 (m, 4H), 6.99 (d, J = 8.4 Hz, 2H), 6.06 (d, J = 3.3 Hz, 1H), 5.16–5.14 (m, 2H), 4.96–4.91 (m, 2H), 4.71 (m, 1H), 4.25 (d, J = 9.3 Hz, 1H), 1.57 (s, 3H), 1.45–1.42 (m, 1H), 1.33 (s, 3H), 0.79–0.70 (m, 2H), 0.58 (m, 1H), 0.47 (m, 1H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 182.4, 167.5, 155.8, 146.2, 146.1, 134.8, 131.1, 130.7, 130.4, 129.2 (2C), 126.1, 125.9, 125.7, 120.5, 120.2, 115.2 (2C), 114.8, 113.5, 112.4, 105.2, 82.1, 80.1, 76.7, 69.8, 53.9, 26.7, 26.2, 16.7, 6.5, 6.1 ppm.

3′-O-(4-(Cyclopropyl(hydroxy)methyl)phenoxy)-1′,2′-O-isopropylidine-α-D-glucofuranoxy-5′-1H-benzo[d][1,2,3]triazole-1-carbothioate (18). Viscous liquid; R_f = 0.50, 60% ethyl acetate/n-hexane); MS: m/z 498 [M + H]⁺; IR (Nujol) ν_max 3568, 2921, 1663, 1557, 1211, 1189, 794, 768, 654 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 8.35 (d, J = 8.1 Hz, 1H), 8.09 (d, J = 8.1 Hz, 1H), 7.60 (dd, J = 7.5, 7.2 Hz, 1H), 7.46 (dd, J = 7.8, 7.2 Hz, 1H), 7.34 (d, J = 8.4 Hz, 2H), 6.97 (d, J = 7.8 Hz, 2H), 6.06 (s, 1H), 5.17–5.16 (m, 2H), 4.94 (d, J = 11.4 Hz, 1H), 4.92 (m, 1H), 4.71 (d, J = 3.0 Hz, 1H), 3.94 (d, J = 8.1 Hz, 1H), 2.18 (bs, 1H), 1.57 (s, 3H), 1.34 (s, 3H), 1.14 (m, 1H), 0.59 (m, 1H), 0.51 (m, 1H), 0.43 (m, 1H), 0.31 (m, 1H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 182.4, 155.7, 146.2, 137.6, 131.1, 130.4, 127.4 (2C), 125.9, 120.4, 115.0 (2C), 114.8, 112.3, 105.2, 82.2, 80.1, 77.7, 77.6, 69.9, 26.7, 26.2, 19.0, 3.4, 2.6 ppm.

5′-O-(Benzothiazol-2-yl)-3′-O-(4-(cyclopropylmethyl)phenyl)-1′,2′-O-isopropylidine-α-D-xylofuranose (19). Viscous liquid; yield 51%; R_f = 0.75 (20% ethyl acetate/n-hexane); 6 equivalents of (TMS)₃SiH has been used. IR (Nujol) ν_max 3013, 1598, 1535, 1075, 1021, 845, 756, 644 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 7.64–7.60 (m, 2H), 7.34–7.32 (m, 3H), 7.20 (dd, J = 7.8, 7.5 Hz, 1H), 6.94 (d, J = 7.8 Hz, 2H), 6.01 (s, 1H), 4.97–4.81 (m, 4H), 4.65 (m, 1H), 3.37–3.34 (m, 1H), 2.04 (d, J = 3.3 Hz, 1H), 1.56 (s, 3H), 1.42–1.40 (m, 1H), 1.32 (s, 3H), 0.73–0.71 (m, 1H), 0.57 (m, 1H), 0.37–0.29 (m, 2H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 172.3, 155.6, 149.0, 137.4, 132.0, 128.4 (2C), 125.9, 123.5, 121.2, 120.8, 115.1 (2C), 112.2, 105.3, 82.0, 80.2, 77.5, 68.8, 48.7, 26.7, 26.2, 20.2, 6.3, 6.0 ppm; MS: m/z 454 [M + H]⁺; anal. calcd for C₂₅H₂₇NO₅S: C, 66.20; H, 6.00; N, 3.09; found: C, 66.37; H, 6.03; N, 3.13.

1-Ferrocenylmethanol (21)²⁶. Red crystals; IR (KBr) ν_max 3507, 2949, 2883, 1563, 1478, 1247, 1149, 884, 745 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 4.32–4.11 (m, 11H), 1.58 (bs, 1H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 83.7, 69.3, 68.4 (3C), 68.2 (4C), 67.8, 60.7 ppm.

O-(Ferrocenylmethyl)-1H-benzo[d][1,2,3]triazole-1-carbothioate (22). The compound 21 (0.434 g, 2.0 mmol) after treatment with 2 (0.59 g, 2.1 mmol) and Et₃N (0.3 equiv.) in dry CH₂Cl₂ (15 mL) was stirred for 6 h at room temperature. The crude product was purified by flash column chromatography (20% ethyl acetate/n-hexane) to afford a red solid, 22, (0.598 g, 79%, R_f = 0.70, 20% ethyl acetate/n-hexane). MS: m/z 378 [M + H]⁺; IR (KBr) ν_max 2945, 1744, 1625, 1609, 1532, 177, 1025, 1008, 936, 714, 598 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 8.19 (d, J = 8.1 Hz, 1H), 8.09 (d, J = 8.1 Hz, 1H), 7.63 (dd, J = 7.2, 7.8 Hz, 1H), 7.47 (dd, J = 7.2, 7.5 Hz, 1H), 4.31 (s, 2H), 4.21 (m, 7H), 4.16 (s, 2H); ¹³C NMR (75 MHz, CDCl₃): δ 168.2, 146.1, 130.7, 130.4, 126.0, 120.2, 113.5, 82.4, 68.8, 68.3, 30.5 ppm.

Methylferrocene (23)²⁷. Orange solid; yield 56%; R_f = 0.75 (20% ethyl acetate/n-hexane); IR (KBr) ν_max 2943, 1555, 1514, 1244, 1186, 1138, 813, 741, 613 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 4.43 (s, 2H), 4.18–4.15 (m, 7H), 1.70 (s, 3H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 83.8, 69.3, 68.99, 68.90, 68.6, 68.2, 67.8, 14.4 ppm.

3,5-Bis((benzyloxy)phenyl)methanol (24a)²⁸. White solid; IR (KBr) ν_max 3567, 2921, 2841, 1578, 1531, 1267, 1178, 1112, 798, 655 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 7.40–7.29 (m, 10H), 6.59 (s, 2H), 6.52 (s, 1H), 4.99 (s, 4H), 4.57 (s, 2H), 1.90 (bs, 1H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 160.0 (2C), 143.3, 136.7 (2C), 128.5 (4C), 127.9 (2C), 127.4 (4C), 105.7, 105.6, 101.1, 70.0 (2C), 65.1 ppm.

(4-(Benzyloxy)-3-methoxyphenyl)methanol (24b)²⁹. White solid; IR (KBr) ν_max 3609, 2944, 1611, 1509, 1498, 1248, 1143, 898, 765 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 7.43–7.27 (m, 5H), 6.92 (s, 1H), 6.83 (dd, J = 8.1, 15.3 Hz, 2H), 5.13 (s, 2H), 4.56 (s, 2H), 3.87 (s, 3H), 1.89 (bs, 1H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 149.7, 147.5, 137.0, 134.1, 128.4 (2C), 127.7, 127.1 (2C), 119.2, 113.9, 110.9, 71.0, 65.1, 55.9 ppm.

O-3,5-Bis(benzyloxy)benzyl-1H-benzo[d][1,2,3]triazole-1-carbothioate (25a). The compound 24a (0.641 g, 2.0 mmol) after treatment with 2 (0.59 g, 2.1 mmol) and Et₃N (0.3 equiv.) in dry CH₂Cl₂ (15 mL) was stirred for 6 h at room temperature. The crude product was purified by flash column chromatography (20% ethyl acetate/n-hexane) to afford a white solid, 25a, (0.78 g, 83%, R_f = 0.60, 20% ethyl acetate/n-hexane); IR (KBr) ν_max 1737, 1641, 1613, 1511, 1164, 1037, 1013, 909, 794, 697 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 8.31 (d, J = 4.2 Hz, 1H), 8.21 (d, J = 5.1 Hz, 1H), 7.60 (dd, J = 7.2, 7.5 Hz, 1H), 7.47 (dd, J = 7.5, 8.1 Hz, 1H), 7.39–7.24 (m, 10H), 6.76 (d, J = 1.5 Hz, 2H), 6.64 (d, 1H), 5.79 (d, J = 3.9 Hz, 2H), 5.05 (d, J = 3.9 Hz, 4H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 180.5, 160.2 (2C), 146.4, 136.5, 135.8, 131.3, 130.4, 128.5 (4C), 128.0 (2C), 127.4 (4C), 125.9, 129.6, 120.5, 114.9, 114.8, 107.5 (2C), 102.6, 74.4, 70.1 ppm.

O-4-(Benzyloxy)-3-methoxybenzyl-1H-benzo[d][1,2,3]triazole-1-carbothioate (25b). The compound 24b (0.49 g, 2.0 mmol) after treatment with 2 (0.59 g, 2.1 mmol) and Et₃N (3.0 equiv.) in dry CH₂Cl₂ (15 mL) was stirred for 6 h at room temperature. The crude product was purified by flash column chromatography (20% ethyl acetate/n-hexane) to afford a white solid, 25b, (0.674 g, 86%), R_f = 0.65 (20% ethyl acetate/n-hexane). MS: m/z 406 [M + H]⁺; IR (KBr) ν_max 1746, 1638, 1510, 1144, 1007, 909, 794, 697 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 8.16 (d, J = 8.4 Hz, 1H), 8.09 (d, J = 8.1 Hz, 1H), 7.63 (dd, J = 7.2, 7.8 Hz, 1H), 7.47 (dd, J = 7.5, 7.8 Hz, 1H), 7.42–7.27 (m, 5H), 6.97 (s, 1H), 6.91 (d, J = 7.8 Hz, 1H), 6.82 (d, J = 8.1 Hz, 1H), 5.13 (s, 2H), 4.35 (s, 2H), 3.89 (s, 3H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 168.0, 149.7, 147.8, 146.1, 136.9, 130.7, 130.4, 128.7, 128.4, 127.8 (2C), 127.1 (2C), 126.1, 121.3, 120.3, 113.9, 113.5, 112.6, 70.9, 55.9, 34.3 ppm.

O-Benzyl 1H-benzo[d][1,2,3]triazole-1-carbothioate (25c)³⁰. The compound 24c (0.217 g, 2.0 mmol) after treatment with 2 (0.59 g, 2.1 mmol) and Et₃N (0.3 equiv.) in dry CH₂Cl₂ (15 mL) was stirred for 6 h at room temperature. The crude product was purified by flash column chromatography (20% ethyl acetate/n-hexane) to afford a white solid, 25c, (0.488 g, 87%, R_f = 0.7, 20% ethyl acetate/n-hexane). IR (KBr) ν_max 1766, 1641, 1565, 1224, 1107, 949, 889, 767, 645 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 8.05 (d, J = 7.8 Hz, 1H), 7.35–7.27 (m, 8H), 5.83 (s, 2H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 169.0, 146.2, 134.7, 132.7, 128.8 (2C), 128.4, 127.5 (2C), 127.3, 123.8, 120.0, 109.6, 52.2 ppm.

O-4-Chlorobenzyl 1H-benzo[d][1,2,3]triazole-1-carbothioate (25d). The compound 24d (0.285 g, 2.0 mmol) after treatment with 2 (0.59 g, 2.1 mmol) and Et₃N (0.3 equiv.) in dry CH₂Cl₂ (15 mL) was stirred for 6 h at room temperature. The crude product was purified by flash column chromatography (20% ethyl acetate/n-hexane) to afford a white solid, 25d, (0.515 g, 85%, R_f = 0.7, 20% ethyl acetate/n-hexane). MS: m/z 305 [M + H] ⁺; IR (KBr) ν_max 1783, 1647, 1557, 1278, 1211, 1048, 879, 765, 655 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 8.06 (d, J = 8.4 Hz, 1H), 7.41–7.31 (m, 3H), 7.28 (d, J = 5.4 Hz, 2H), 7.18 (d, J = 5.4 Hz, 2H), 5.79 (s, 2H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 168.9, 146.2, 134.3, 133.1, 132.5, 129.1 (2C), 128.8 (2C), 127.5, 123.9, 120.0, 109.4, 51.3 ppm.

(((5-Methyl-1,3-phenylene)bis(oxy))bis(methylene))dibenzene (26a)³¹. White solid; yield 58%; R_f = 0.8 (20% ethyl acetate/n-hexane); IR (KBr) ν_max 2925, 1539, 1508, 1244, 1231, 1043, 1012, 576 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 7.38–7.33 (m, 10H), 6.63 (s, 1H), 6.58 (d, J = 2.4 Hz, 1H), 5.40 (s, 1H), 5.02 (s, 2H), 5.00 (s, 2H), 2.34 (s, 3H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 160.0 (2C), 136.7 (2C), 136.6 (2C), 128.5 (4C), 128.0 (2C), 127.5 (4C), 107.3, 70.2, 70.1, 21.3 ppm.

1-(Benzyloxy)-2-methoxy-4-methylbenzene (26b)³². White solid; yield 60%; R_f = 0.7 (20% ethyl acetate/n-hexane); IR (KBr) ν_max 1573, 1510, 1277, 1232, 1167, 1109, 798, 7761, 629, 534 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 7.41–7.28 (m, 5H), 6.77 (s, 2H), 6.67 (d, J = 6.9 Hz, 1H), 5.13 (s, 2H), 3.87 (s, 3H), 2.37 (s, 3H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 158.4, 149.5, 147.5, 136.9, 130.34, 130.31, 128.5, 127.8, 127.1, 121.5, 113.7, 112.9, 71.0, 56.0, 21.3 ppm.

Toluene (26c)³³. Not isolated.

p-Chloro toluene (26d)³⁴. Liquid; yield 66%; R_f = 0.8 (10% ethyl acetate/n-hexane); ¹H NMR (300 MHz, CDCl₃): δ 7.19 (d, J = 8.1 Hz, 2H), 7.06 (d, J = 7.8 Hz, 2H), 2.29 (s, 3H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 136.1, 131.0, 130.3 (2C), 128.2 (2C), 20.8 ppm.

O-(4-Methoxyphenyl)-1H-benzo[d][1,2,3]triazole-1-carbothioate (28)³⁰. Orange crystals, 0.667 g, yield 68%; R_f = 0.7 (20% ethyl acetate/n-hexane); IR (KBr) ν_max 3234, 2973, 1564, 1525, 1452, 1367, 1023, 1011, 842, 758 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 8.50 (d, J = 8.1 Hz, 1H), 8.19 (d, J = 7.8 Hz, 1H), 7.70 (dd, J = 7.5, 7.8 Hz, 1H), 7.32 (d, J = 8.1 Hz, 2H), 7.15 (d, J = 8.1 Hz, 2H), 2.43 (s, 3H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 182.4, 150.5, 146.6, 137.1, 131.7, 130.7, 130.4 (2C), 126.2, 121.6 (2C), 120.8, 115.1, 21.0 ppm.

2-(4-Methoxyphenoxy)benzo[d]thiazole (29)³⁵. White solid, 0.196 g, yield 87%; R_f = 0.8 (20% ethyl acetate/n-hexane); IR (KBr) ν_max 3259, 2942, 1569, 1555, 1465, 1235, 1047, 745, 665 cm⁻¹; ¹H NMR (300 MHz, CDCl₃): δ 7.86 (d, J = 7.8 Hz, 1H), 7.61 (d, J = 7.8 Hz, 3H), 7.37 (t, J = 7.5 Hz, 1H), 7.28–7.20 (m, 4H), 2.39 (s, 3H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 172.8, 153.8, 139.8, 136.4 (2C), 131.1 (3C), 127.8, 126.4, 124.3, 121.3, 120.2, 22.7 ppm.

1-Ferrocenylethanol (30)³⁶. Orange solid; ¹H NMR (300 MHz, CDCl₃): δ 4.53 (m, 1H), 4.18–4.15 (m, 9H), 1.88 (bs, 1H), 1.43 (d, J = 6.0 Hz, 3H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 94.7, 68.2 (4C), 67.8 (2C), 66.0 (2C), 65.5, 23.6 ppm.

1-Ferrocenyl-1-(1N-benzotriazolyl)ethane (31). Red crystals; ¹H NMR (300 MHz, CDCl₃): δ 8.02 (d, J = 7.8 Hz, 1H), 7.35–7.28 (m, 3H), 6.13–6.07 (m, 1H), 4.38 (s, 1H), 4.19–4.10 (m, 8H), 2.03 (d, J = 7.2 Hz, 3H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 146.2, 131.6 (2C), 126.7, 123.5, 119.9, 110.4, 87.2, 69.0, 68.9, 68.8, 68.7, 68.2, 68.0, 67.9, 67.8, 66.6, 66.4, 55.7, 55.6, 20.1 ppm.

1-Ferrocenyl-1-(2N-benzotriazolyl)ethane (32). Red crystals, MS: m/z 332 [M + H]⁺; ¹H NMR (300 MHz, CDCl₃): δ 7.84 (d, J = 3.3 Hz, 2H), 7.34 (d, J = 3.3 Hz, 2H), 5.98–5.96 (m, 1H), 4.38 (s, 1H), 4.32 (s, 1H), 4.13–4.03 (m, 7H), 2.06 (d, J = 6.6 Hz, 3H) ppm; ¹³C NMR (75 MHz, CDCl₃): δ 143.8, 126.0 (2C), 118.1 (2C), 88.0, 68.9, 68.7, 68.5, 68.4, 68.0, 67.9, 67.8, 67.6, 66.6, 66.5, 62.6, 62.5 ppm.

Acknowledgements

The authors thank CISC, Banaras Hindu University and IIT Delhi for spectroscopic studies. VKT thank Council of Scientific and Industrial Research for funding (Grant no. 02(0173)/13/EMR-II) and Dr R. P. Tripathi Sc F at CDRI Lucknow for his help during the investigation.

Notes and references

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Footnotes

† Electronic supplementary information (ESI) available: Copies of ¹H and ¹³C NMR spectra for all the synthesized compounds and single crystal X-ray crystallographic data for compounds 28, 31 and 32 has been provided. CCDC 978009–978011. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5ra01545f

‡ Present address: Department of Chemistry, Indian Institute of Technology-Delhi, New Delhi, 110016, India.

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