InCl₃ catalyzed domino route to 2H-chromene-2-ones via [4 + 2] annulation of 2-hydroxyarylaldehydes with α-oxoketene dithioacetal under solvent-free conditions

Abstract

A facile and efficient synthesis of 3-aroyl/heteroaroyl/ferrocenoyl/alkanoyl-2H-chromen-2-ones has been developed by the cyclocondensation of α-oxoketene dithioacetals and 2-hydroxyarylaldehydes catalyzed by InCl₃ under solvent-free conditions. No co-catalyst or activator is needed and MeSH is the only by-product of this protocol. The methodology involves ring annulation of 2-hydroxyarylaldehydes with a variety of α-oxoketene dithioacetals offering rapid entry into differentially substituted chromen-2-ones. The condensation of ferrocene derived α-oxoketene dithioacetal and 2-hydroxyarylaldehyde furnished coumarin installed on a ferrocene platform.

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Introduction

The coumarins (2H-chromen-2-ones, 2H-1-benzopyran-2-ones), an elite class of lactones, are important oxygen heterocycles that are widely present as a structural motif in numerous natural products.¹ Among the scaffolds of natural products, coumarins exhibit a broad range of biological² and therapeutic³ activities together with various applications in technological⁴ fields. Since the first isolation of coumarin in 1820, over 1400 natural coumarins have been isolated from natural sources, and their pharmacological and biochemical properties depend upon the pattern of substitutions. Several synthetic analogs of the coumarin such as novobiocin, chlorobiocin, coumermycin, simocyclinone, demiflin, and flavaxate have been developed into useful drugs.⁵Xanthotoxol (8-hydroxylpsoralen, Xan 1) is a natural psoralen with high capacity for the treatment of Alzheimer's disease^6a and 4-(4-phenoxybutoxy)-7H-furo[3,2-g]chromene-7-thione, 2 is a blocker^6b of the lymphocyte potassium channel Kv1.3. Scopoletin (7-hydroxy-6-methoxycoumarin) shows inhibitory activities on brain acetylcholinesterase.^6cDibromo-7-hydroxy-4-methylchromen-2-one^7a (DBC, 3), is the most promising inhibitor of Casein Kinase 2 (CK2). Other coumarin derivatives such as calanolide A 4, phenprocoumon 5, and warfarin 6 have been reported as potent anti-HIV agents.^7bNovobiocin⁸7 and its analogues have been shown to bind the C-terminal domain of heat-shock protein 90 (hsp90), an exciting new target in cancer drug discovery⁹ that lead to a decrease in hsp90 client proteins in various cancer cell lines¹⁰ (Chart 1).

Chart 1 Some biologically active coumarins.

Coumarin, having an aldehyde group, was prepared as a doubly activated Michael acceptor and evaluated as a colorimetric and fluorescent probe for cyanide in water.¹¹ Moreover, 3-aroylcoumarins are good Michael acceptors, amenable to further synthetic transformations,¹² and demonstrated important roles in monoamine oxidase (MAO) enzymatic inhibition.¹³

Several elegant strategies¹⁴ for the syntheses of coumarins involving different types of catalysts have been developed.¹⁵ In recent years, versatile coumarin syntheses could be achieved through organopalladium intermediates.¹⁶ A few combinatorial library syntheses of derivatives of this important scaffold have also been developed, principally to test their utility as drug candidates.¹⁷ Among them, domino synthesis of coumarins has proved to be one of the most attractive methods, but only few reports^18a,b are currently known. However, the reports on the synthesis of chromene-2-ones from α-oxoketene dithioacetals are limited,^18a,b and suffer from drawbacks, such as long reaction times, harsh reaction conditions, and a lack of generality. Because of the great relevance to both synthetic and medicinal chemists, exploration of coumarins for drug discovery has been a vital subject of constant interest, and there has been a continuous effort to develop new, convenient, and versatile methods with defined structural features. Recently, indium trichloride has emerged as a powerful green and potential Lewis acid catalyst imparting high regio-and chemoselectivity in various chemical transformations,¹⁹ due to its low toxicity, air and water compatibility, operational simplicity, and remarkable ability to suppress side reactions in acid sensitive substrates.

In continuation of our efforts on the development of synthetic methodologies for heterocycles²⁰ and our current interest in polarized ketene acetals,²¹ we report for the first time a two-component condensation of 2-hydroxyarylaldehydes and α-oxoketene dithioacetals in the presence of InCl₃ under solvent-free conditions. Condensations occurred rapidly and were completed within two hours, consuming both the starting materials completely to give good yields. This procedure offers a selective and straightforward approach to various 3-substituted-2H-chromene-2-ones 10 and benzo[f]2H-chromene-2-ones 12. The generality of this protocol has been established with several examples.

Results and discussion

Our literature survey at this stage revealed that the α-oxoketene dithioacetals have been shown to be a important class of versatile intermediates, which have been exploited extensively in many synthetic transformations.²² The desired α-oxoketene dithioacetals 8 were prepared in good yields by treating the corresponding aryl/heteroaryl/aliphatic ketones with carbon disulphide in the presence of potassium tert-butoxide followed by alkylation with methyl iodide (Scheme 1).¹⁸ The β-alkylthio groups in this intermediate are activated by the presence of the polar carbonyl group at the α-position, and can therefore be displaced sequentially by various nucleophiles, creating further scope for introducing new functionalities at the β-position, which may find applications in many synthetic transformations.

Scheme 1 Synthesis of α-oxoketene dithioacetals 8a–k.

Recently, we have succeeded on the straightforward syntheses of chromene-2-thiones via ring annulation of β-oxodithioesters^20f under solvent-free conditions. The key strategy relies on the creation of a pyran ring through Lewis acid-catalyzed condensation. We envisioned that the similar construction of a pyran ring might be subsequently achieved via intermolecular cyclocondensation between α-oxoketene dithioacetal and 2-hydroxyarylaldehyde in the presence of Lewis acid catalyst under solvent-free conditions. It is worth noting that Rao et al.^18a utilized α-aroylketene dithioacetals for the first time for the synthesis of 3-aroylcoumarins in the presence of piperidine in THF, which required a longer reaction time (12–15 h) and a high temperature (80 °C). In the present work 3-aroylcoumarins have been synthesized utilizing α-oxoketene dithioacetals in the presence of InCl₃ at 65 °C under solvent-free conditions within 2 h.

The synthesis of 3-aroyl-2H-chromene-2-ones 10 was first undertaken. Indeed, our first attempt began with the condensation of 3,3-bis(methylthio)-1-(4-methoxyphenyl)-propen-1-one 8a (1 equiv) with salicylaldehyde 9a (1 equiv) as a model substrate. The reaction took place smoothly in the presence of InCl₃ (10 mol%) under solvent-free conditions at 65 °C to give the desired product 3-(4-methoxybenzoyl)-2H-chromene-2-one (10a) in 94% yield (Table 1, entry 1). The above model reaction was investigated under a variety of conditions (catalyst, solvent, solvent-free, temperature, and time), as a test case to optimize the reaction conditions, and the results are gathered in Table 1.

Table 1 Optimization of reaction conditions^a for the synthesis of chromene-2-ones

Entry	Catalyst (mol%)	Solvent	T/°C	Time	Yield (%)^b
a Reaction of 3,3-bis(methylthio)-1-(4-methoxyphenyl)-propen-1-one (1 mmol) with salicylaldehyde (1 mmol). b Isolated yields.
1	InCl3 (10)	None	65	0.5 h	94
2	SbCl3 (10)	None	65	10 h	48
3	CuBr2 (10)	None	65	4 h	78
4	p-TSA (10)	None	65	10 h	45
5	SiO2–H2SO4(10)	None	65	8 h	40
6	SiO2–HClO4(10)	None	65	6 h	46
7	InCl3 (5)	None	65	1 h	82
8	InCl3 (20)	None	65	25 min	92
9	InCl3 (10)	None	40	1.5 h	64
10	InCl3 (10)	None	55	1.0 h	76
11	InCl3 (10)	None	80	0.5 h	92
12	InCl3 (10)	C6H6	Reflux	24 h	trace
13	InCl3 (10)	CHCl3	Reflux	24 h	No reaction
14	InCl3 (10)	THF	Reflux	24 h	No reaction
15	InCl3 (10)	CH3CN	Reflux	24 h	No reaction
16	InCl3 (10)	DMF	Reflux	24 h	trace
17	InCl3 (10)	EtOH	Reflux	24 h	No reaction
18	None	None	65	24 h	No reaction

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A control experiment with the above model substrates in the absence of catalyst did not provide the desired products (Table 1, entry 18). Initially, a variety of catalysts such as InCl₃, H₂SO₄–SiO₂, SbCl₃, p-TSA, CuBr₂ and HClO₄–SiO₂ were screened to identify a suitable promoter for this transformation. Both InCl₃ and CuBr₂ facilitated chromene-2-one formation but InCl₃ was found to be better than CuBr₂ in terms of yield and time (Table 1, entries 1 and 3). In order to evaluate the most appropriate loading of InCl₃, the above model reaction was performed with varying loading percentages, and it was found that 10 mol% of InCl₃ was sufficient enough to promote the reaction. Further screening of non-polar, polar-aprotic, and polar-protic solvents such as C₆H₆, CHCl₃, THF, DMF, CH₃CN, and EtOH revealed that solvent-free conditions were found to be the best choice, which furnished the products not only in excellent yields but also with higher reaction rates. In addition, the effect of temperature was also studied, and the optimum temperature of the reaction was found to be 65 °C. Increasing the temperature above 65 °C neither improved the yield nor reduced the reaction time considerably; whereas lowering the temperature resulted in longer reaction times (Table 1, entry 9). Thus, the optimum condition was found to be 10 mol% of InCl₃ at 65 °C under solvent-free conditions. Overall, the method works well and tolerates a variety of electron-rich and electron-deficient groups in the salicylaldehyde as well as on the aromatic ring of the α-aroylketene dithioacetal.

To test generality and scope of the condensation, and to generate a small combinatorial library of functionalized 3-substituted chromene-2-ones 10 using the optimized reaction condition, eleven α-oxoketene dithioacetals 8a–k were treated with six 2-hydroxyarylaldehydes 9a–f to furnish eighteen aroyl coumarins 10 in good yields (Scheme 2).

Scheme 2 Synthesis of 3-aroyl-2H-chromene-2-ones 10.

A number of functional groups, such as bromo, nitro, methoxy, and ethoxy in the salicylaldehyde component, and methoxy, methyl, phenyl, chloro and bromo groups at the o-and p-positions of the α-aroylketene dithioacetals 8a–g are well tolerated under the reaction conditions to provide structurally interesting chromene-2-ones 10 in good yields. All the reactions were monitored by TLC up to the total consumption of the starting materials, which required 0.5–2.0 h for their completion. All products were purified either by recrystallization or by column chromatography on silica gel.

To further add diversity to the chromene-2-one framework, the ketene dithioacetals 8h and 8i were subjected to cyclocondensation with 2-hydroxyarylaldehydes 9a–c and 9f to afford 3-heteroaroyl-2H-chromene-2-ones 10 in good yields (Scheme 3).

Scheme 3 Synthesis of 3-heteroaroyl-2H-chromene-2-ones 10.

As a next attempt, we have installed the coumarin motif on a ferrocene platform following the method presently developed. The ferrocene based α-oxoketene dithioacetal 8j was smoothly transformed into 3-η⁵-ferrocenoyl-2H-chromene-2-ones 10ja–je by condensation with 2-hydroxyarylaldehyde 9a–e under the above optimized conditions (Scheme 4). The α-oxoketene dithioacetal 8j was prepared from acetyl ferrocene by reaction with carbon disulfide and sodium tert-butoxide followed by alkylation with methyl iodide.

Scheme 4 Synthesis of 3-ferrocenoyl-2H-chromene-2-ones 10.

Similarly, 3-tert-butanoyl-2H-chromen-2-ones could be obtained by treatment of α-oxoketene dithioacetal 8k with 2-hydroxyarylaldehydes 9b, 9e, and 9f under identical conditions. As expected, all the reactions proceeded smoothly to afford coumarins10kb, 10ke, and 10kf in 80–82% yields (Scheme 5). The α-oxoketene dithioacetal 8k was prepared from tert-butyl methyl ketone by reaction with carbon disulfide and sodium tert-butoxide followed by alkylation.

Scheme 5 Synthesis of 3-tert-butanoyl-2H-chromene-2-ones 10.

In a further elaboration to construct novel benzo[f]2H-chromene-2-ones, and to explore the limitations and generality of the reaction, 2-hydroxy-1-naphthaldehyde 11 as a cyclocondensation partner was treated with various α-oxoketene dithioacetals 8a–k under optimized reaction conditions to afford benzo[f]2H-chromene-2-ones 12a–k in 78–90% yields (Scheme 6). Such coumarins exhibit characteristics of triplet sensitizers, particularly when there is extended conjugation to aromatic rings.

Scheme 6 Synthesis of 3-substituted benzo[f]2H-chromene-2-ones 12.

The structural determination of all the products 10 and 12 was achieved by IR, ¹H and ¹³C NMR, and MS spectral analyses, and unequivocally established by X-ray single crystal diffraction analysis of two representative compounds 3-(ferrocene-2-carbonyl)-chromen-2-one10ja and 3-(2-chlorobenzoyl) benzo[f]chromen-2-one 12f. The ORTEP drawing of 10ja and 12f are presented in Fig. 1, and their CIF data are given in the ESI†.

Fig. 1 ORTEP diagram of 10ja and 12f respectively.

On the basis of the above experimental results together with the related reports, a plausible reaction scenario for this two-component cyclocondensation reaction is proposed and outlined in Scheme 7. The α-oxoketene dithioacetals 8 are polarized alkenes (polarization flows from two electron-donating alkylthio groups on C-1 to the electron-withdrawing carbonyl group on C-2), showing C-1 electrophilic and C-2 nucleophilic characteristics. First, an oxa-Michael type reaction of 2-hydroxyarylaldehyde 9 or 11 (molecule with nucleophilic oxygen and electrophilic carbonyl carbon) on the C-1 of the α-oxoketene dithioacetal 8 occurs to generate enolate A, which undergoes intramolecular cyclization to produce Bvia aldol type condensation. The intermediate B immediately undergoes dehydration to give C, which upon subsequent hydrolysis of methylthio groups (by the H₂O released during dehydration) with the extrusion of MeSH leads to 3-substituted coumarins 10 and 12. This operationally simple and two-component domino process concomitantly created two chemical bonds (one C–O bond and one C–C bond) leading to a new pyran ring.

Scheme 7 Plausible mechanism for the synthesis of chromen-2-ones.

In summary, we have developed a highly efficient two-component synthesis of 3-substituted-2H-chromene-2-ones 10 and benzo[f]2H-chromene-2-ones 12 from α-oxoketene dithioacetals and 2-hydroxyarylaldehydes in high yields under solvent-free conditions in the presence of InCl₃. In this experimentally simple process, one C–O bond, one C–C bond, and one new pyran ring are constructed with both reactants efficiently utilized. The scaffold could be further decorated to introduce more diversity through subsequent coupling reaction. The facile assembly of a 2H-chromene-2-one library could be expected because of the high efficiency, good substrate generality, mild conditions, and the ready availability of the starting materials.

Experimental

All starting materials were commercially available and used as received without further purification. α-Oxoketene dithioacetals (8a–k) were prepared according to the protocol described in literature¹⁸ and displayed in Scheme 1. Thin layer chromatography (TLC) was performed using silica gel 60 F₂₅₄ precoated plates. Infrared (IR) spectra are measured in KBr and wavelengths are reported in cm⁻¹. ¹H and ¹³C NMR spectra were recorded on NMR spectrometer operating at 300 and 75 MHz, respectively. Chemical shifts (δ) are given in parts per million (ppm) using the residue solvent peaks as reference relative to TMS. J values are given in Hz. Mass spectra (MS) were recorded using Electron-spray ionization (ESI) mass spectrometry. The C, H, and N analyses were performed from microanalytical laboratory. The melting points are uncorrected.

General procedure for synthesis of α-oxoketene dithioacetals¹⁸ (8a–k)

To a stirred suspension of Potassium tert-butoxide (4.48 g, 40 mmol) in dry THF (10 mL) at 0 °C, a solution of ketone (10 mmol) and carbon disulfide (12 mmol, 0.913 g, 0.73 mL) in dry THF (10 mL) was added dropwise. The reaction mixture was vigorously stirred at 0 °C for 90 min. To this suspension, a solution of methyl iodide (22 mmol, 1.37 mL) in dry THF (5 mL) was added dropwise during 10 min at 0 °C. The reaction mixture was allowed to stir for 3 h. After completion of the reaction (monitored by TLC), the mixture was poured over crushed ice/saturated ammonium chloride solution, and extracted using ethyl acetate (3 × 25 mL). The combined organic extract was washed with brine (1 × 25 mL), dried, and concentrated under vacuum to obtain the crude product, which was finally purified by silica gel column chromatography using ethyl acetate-n-hexane (1 : 10) as eluent. Spectral and analytical data of representative α-oxoketene dithioacetals are given below.

1-(4-Methoxyphenyl)-3,3-[bis(methylthio)]-propenone (8a). Yellow solid: mp 103–104 °C . ¹H NMR (300 MHz, CDCl₃): δ 7.91 (d, J = 8.7 Hz, 2H, ArH), 6.92 (d, J = 8.7 Hz, 2H, ArH), 6.74 (s, 1H, CH), 3.86 (s, 3H, OCH₃), 2.55 and 2.52 (2s, 6H, 2 × SCH₃). ¹³C NMR (75 MHz, CDCl₃): δ 184.5, 164.8, 162.4, 132.0, 129.8, 113.5, 109.3, 55.3, 17.2, 15.0. IR (KBr, cm⁻¹): 3057, 2915, 1599, 1473, 1232, 1165, 774. ESI MS (m/z): 255 (M⁺+1); Anal. Calcd for C₁₂H₁₄O₂S₂: C, 56.66; H, 5.55. Found: C, 56.81; H, 5.41.

1-Biphenyl-4-yl-3,3-[bis(methylthio)]-propenone (8g). Yellow solid: mp 119–120 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.99 (d, J = 8.1 Hz, 2H, ArH), 7.67–7.61 (m, 4H, ArH), 7.48–7.35 (m, 3H, ArH), 6.81 (s, 1H, CH), 2.58 and 2.54 (2s, 6H, 2 × SCH₃). ¹³C NMR (75 MHz, CDCl₃): δ 185.1, 166.3, 144.3, 140.0, 138.0, 128.8, 128.2, 127.9, 127.2, 127.1, 109.3, 17.3, 15.0. IR (KBr, cm⁻¹): 3049, 2935, 1615, 1451, 1247, 1161, 792. ESI MS (m/z): 301 (M⁺+1); Anal. Calcd for C₁₇H₁₆OS₂: C, 67.96; H, 5.37. Found: C, 67.73; H, 5.58.

1-Furan-2-yl-3,3-[bis(methylthio)]-propenone (8h). Yellow solid: mp 115–116 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.51 (s, 1H, ArH), 7.15 (d, J = 3.3 Hz, 1H, ArH), 6.71 (s, 1H, CH), 6.51 (s, 1H, ArH), 2.56 and 2.52 (2s, 6H, 2 × SCH₃). ¹³C NMR (75 MHz, CDCl₃): δ 174.5, 166.2, 153.9, 144.7, 115.0, 112.2, 108.6, 17.2, 14.9. IR (KBr, cm⁻¹): 3104, 2914, 1610, 1495, 1460, 1260, 1077, 912, 779. ESI MS (m/z): 215 (M⁺+1); Anal. Calcd for C₉H₁₀O₂S₂: C, 50.44; H, 4.70. Found: C, 50.63; H, 4.57.

3,3-[Bis(methylthio)]-1-ferrocen-2-yl-propenone (8j). Red solid: mp 132–133 °C. ¹H NMR (300 MHz, CDCl₃): δ 6.34 (s, 1H, CH), 4.78 (s, 2H, H_cp), 4.45 (s, 2H, H_cp), 4.18 (s, 5H, H_cp), 2.53 and 2.50 (2s, 6H, 2 × SCH₃). ¹³C NMR (75 MHz, CDCl₃): δ 189.3, 161.5, 111.2, 71.6, 69.8, 69.1, 17.3, 14.9. IR (KBr, cm⁻¹): 3106, 2918, 1608, 1494, 1250, 1100, 765. ESI MS (m/z): 333 (M⁺+1); Anal. Calcd for C₁₅H₁₆FeOS₂: C, 54.22; H, 4.85. Found: C, 54.31; H, 4.99.

4,4-Dimethyl-1,1-[bis(methylthio)]-pent-1-en-3-one (8k). Orange solid: mp 61–62 °C. ¹H NMR (300 MHz, CDCl₃): δ 6.28 (s, 1H, CH), 2.46 (s, 6H, 2 × SCH₃), 1.18 (s, 9H, 3 × CH₃). ¹³C NMR (75 MHz, CDCl₃): δ 200.6, 163.6, 108.6, 42.7, 27.0, 17.0, 14.7. IR (KBr, cm⁻¹): 1742, 1701, 1636, 1475, 1426, 1108. ESI MS (m/z): 205 (M⁺+1); Anal. Calcd for C₉H₁₆OS₂: C, 52.90; H, 7.89. Found: C, 53.01; H, 7.99.

General procedure for the synthesis of 3-substituted coumarins (10 and 12)

A mixture of α-oxoketene dithioacetal 8 (1.0 mmol) and salicylaldehyde 9 or 2-hydroxy-1-naphthaldehyde 11 (1.0 mmol) were treated in the presence of InCl₃ (10 mol%, 0.1 mmol, 0.022 g) with constant stirring at 65 °C. The heating was continued for the stipulated period of time (0.5–2.0 h) till the completion of the reaction (monitored by TLC). The reaction mixture was treated with water (20 mL) and extracted with ethyl acetate (2 × 20 mL). The organic layer was washed with brine (1 × 20 mL) and dried over anhyd. Na₂SO₄. The solvent was evaporated under vacuum to give the product, which was purified either by recrystallization from ethanol or by column chromatography over silica gel using ethyl acetate-n-hexane (1 : 8) as eluent. Spectral data of all new compounds are given below.

6-Bromo-3-(4-methoxybenzoyl)-chromen-2-one (10ab). White solid: mp 173–174 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.91 (s, 1H, ArH), 7.86 (d, J = 8.7 Hz, 2H, ArH), 7.73–7.69 (m, 2H, ArH), 7.31–7.27 (m, 2H, ArH), 6.95 (d, J = 9.0 Hz, 2H, ArH), 3.89 (s, 3H, OCH₃). ¹³C NMR (75 MHz, CDCl₃): δ 189.3, 164.4, 153.3, 142.8, 139.9, 132.1, 131.0, 128.7, 119.7, 118.6, 117.4, 114.0, 55.5. IR (KBr, cm⁻¹): 3093, 2929, 1720, 1647, 1601, 1553, 1512, 1255, 1171. ESI MS (m/z): 359 (M⁺+1); Anal. Calcd for C₁₇H₁₁BrO₄: C, 56.85; H, 3.09. Found: C, 56.91; H, 3.26.

3-(4-Chlorobenzoyl)-6-nitro-chromen-2-one (10bd). White solid: mp 242–243 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.55–8.49 (m, 2H, ArH), 8.15 (s, 1H, ArH), 7.84–7.79 (m, 2H, ArH), 7.57–7.47 (m, 3H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ 189.2, 157.9, 144.3, 144.0, 140.9, 133.8, 130.9, 129.1, 128.7, 128.1, 124.8, 118.2, 118.0. IR (KBr, cm⁻¹): 2929, 2859, 1727, 1657, 1617, 1536, 1346, 1246. ESI MS (m/z): 330 (M⁺+1); Anal. Calcd for C₁₆H₈ClNO₅: C, 58.29; H, 2.45; N, 4.25. Found: C, 58.41; H, 2.37; N, 4.09.

3-(4-Chlorobenzoyl)-8-ethoxy-chromen-2-one (10be). White solid: mp 228–229 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.09 (s, 1H, ArH), 7.81 (d, J = 8.4 Hz, 2H, ArH), 7.44 (d, J = 8.4 Hz, 2H, ArH), 7.24–7.15 (m, 3H, ArH), 4.21 (q, J = 6.9 Hz, 2H, OCH₂), 1.53 (t, J = 6.9 Hz, 3H, CH₃). ¹³C NMR (75 MHz, CDCl₃): δ 190.6, 158.1, 146.6, 146.3, 144.7, 140.2, 134.5, 130.9, 128.8, 126.7, 124.9, 120.3, 118.8, 116.5, 65.0, 14.7. IR (KBr, cm⁻¹): 2989, 2929, 1716, 1657, 1603, 1467, 1280, 1244. ESI MS (m/z): 329 (M⁺+1); Anal. Calcd for C₁₈H₁₃ClO₄: C, 65.76; H, 3.99. Found: C, 65.97; H, 4.11.

6-Bromo-3-(4-methylbenzoyl)-chromen-2-one (10cb). White solid: mp 219–220 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.93 (s, 1H, ArH), 7.77 (d, J = 8.1 Hz, 2H, ArH), 7.72–7.70 (m, 2H, ArH), 7.31–7.25 (m, 3H, ArH), 2.43 (s, 3H, ArCH₃). ¹³C NMR (75 MHz, CDCl₃): δ 190.6, 157.7, 153.4, 145.2, 143.3, 136.0, 133.2, 131.1, 129.7, 129.3, 128.3, 119.6, 118.6, 117.4, 21.8. IR (KBr, cm⁻¹): 3055, 1722, 1653, 1607, 1478, 1287. ESI MS (m/z): 343 (M⁺+1); Anal. Calcd for C₁₇H₁₁BrO₃: C, 59.50; H, 3.23. Found: C, 59.42; H, 3.38.

3-(4-methylbenzoyl)-6-nitro-chromen-2-one (10cd). White solid: mp 192–193 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.52–8.48 (m, 2H, ArH), 8.07 (s, 1H, ArH), 7.78 (d, J = 8.1 Hz, 2H, ArH), 7.54 (d, J = 8.7 Hz, 1H, ArH), 7.31 (d, J = 7.8 Hz, 2H, ArH), 2.45 (s, 3H, ArCH₃). ¹³C NMR (75 MHz, CDCl₃): δ 189.8, 157.8, 156.8, 145.6, 144.3, 143.0, 132.9, 129.8, 129.5, 127.8, 124.7, 118.1, 21.8. IR (KBr, cm⁻¹): 3061, 1736, 1658, 1615, 1528, 1346, 1250. ESI MS (m/z): 310 (M⁺+1); Anal. Calcd for C₁₇H₁₁NO₅: C, 66.02; H, 3.58; N, 4.53. Found: C, 66.25; H, 3.43; N, 4.86.

8-Ethoxy-3-(4-methylbenzoyl)-chromen-2-one (10ce). White solid: mp 130–131 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.02 (s, 1H, ArH), 7.78 (d, J = 7.8 Hz, 2H, ArH), 7.27–7.12 (m, 5H, ArH), 4.21 (q, J = 6.9 Hz, 2H, OCH₂), 2.42 (s, 3H, ArCH₃), 1.52 (t, J = 6.9 Hz, 3H, CH₃). ¹³C NMR (75 MHz, CDCl₃): δ 191.2, 158.0, 146.4, 145.2, 144.8, 144.4, 133.5, 129.7, 129.2, 127.3, 124.7, 120.1, 118.8, 116.2, 64.9, 21.7, 14.6. IR (KBr, cm⁻¹): 2988, 2920, 1717, 1657, 1606, 1467, 1279, 1244, 1110. ESI MS (m/z): 309 (M⁺+1); Anal. Calcd for C₁₉H₁₆O₄: C, 74.01; H, 5.23. Found: C, 73.92; H, 5.39.

3-Benzoyl-8-ethoxychromen-2-one (10de). White solid: mp 144–145 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.05 (s, 1H, ArH), 7.88 (d, J = 7.5 Hz, 2H, ArH), 7.63–7.58 (m, 1H, ArH), 7.49–7.44 (m, 2H, ArH), 7.28–7.23 (m, 1H, ArH), 7.18–7.13 (m, 2H, ArH), 4.21 (q, J = 6.9 Hz, 2H, OCH₂), 1.52 (t, J = 6.9 Hz, 3H, CH₃). ¹³C NMR (75 MHz, CDCl₃): δ 191.7, 158.0, 146.5, 145.6, 144.5, 136.1, 133.7, 129.5, 128.5, 127.1, 124.7, 120.2, 118.8, 116.3, 65.0, 14.6. IR (KBr, cm⁻¹): 3061, 2981, 1707, 1659, 1607, 1467, 1279, 1241, 1097. ESI MS (m/z): 295 (M⁺+1); Anal. Calcd for C₁₈H₁₄O₄: C, 73.46; H, 4.79. Found: C, 73.59; H, 4.65.

3-Benzoyl-8-phenylchromen-2-one (10df). White solid: mp 178–179 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.13 (s, 1H, ArH), 7.89 (d, J = 8.1 Hz, 2H, ArH), 7.70 (d, J = 7.5 Hz, 1H, ArH), 7.64–7.57 (m, 4H, ArH), 7.51–7.39 (m, 6H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ 191.6, 158.0, 151.5, 145.8, 136.1, 135.0, 134.7, 133.8, 130.4, 129.6, 129.4, 128.5, 128.4, 128.2, 126.9, 124.9, 118.6. IR (KBr, cm⁻¹): 3060, 2923, 1716, 1655, 1595, 1452, 1168. ESI MS (m/z): 327 (M⁺+1); Anal. Calcd for C₂₂H₁₄O₃: C, 80.97; H, 4.32. Found: C, 80.82; H, 4.45.

3-(4-Bromobenzoyl)-6-nitrochromen-2-one (10ed). White solid: mp 267–268 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.54–8.49 (m, 2H, ArH), 8.15 (s, 1H, ArH), 7.73 (d, J = 8.4 Hz, 2H, ArH), 7.65 (d, J = 8.4 Hz, 2H, ArH), 7.55 (d, J = 8.7 Hz, 1H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ 189.5, 158.1, 150.1, 145.2, 144.5, 141.1, 133.2, 130.5, 129.3, 128.3, 127.4, 125.1, 118.6, 117.9. IR (KBr, cm⁻¹): 2960, 1740, 1652, 1614, 1532, 1347, 1251, 1157. ESI MS (m/z): 374 (M⁺+1); Anal. Calcd for C₁₆H₈BrNO₅: C, 51.36; H, 2.16; N, 3.74. Found: C, 51.21; H, 2.32; N, 3.46.

3-(4-Bromobenzoyl)-8-phenylchromen-2-one (10ef). White solid: mp 192–193 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.18 (s, 1H, ArH), 7.76–7.70 (m, 3H, ArH), 7.63–7.59 (m, 5H, ArH), 7.52–7.40 (m, 4H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ 190.7, 158.0, 151.6, 146.4, 135.0, 134.9, 131.8, 130.9, 130.5, 129.4, 129.0, 128.5, 128.3, 126.4, 125.0, 118.5. IR (KBr, cm⁻¹): 2924, 1721, 1656, 1592, 1456, 1277, 1239, 1172. ESI MS (m/z): 405 (M⁺+1); Anal. Calcd for C₂₂H₁₃BrO₃: C, 65.20; H, 3.23. Found: C, 65.37; H, 3.36.

6-Bromo-3-(2-Chlorobenzoyl)-chromen-2-one (10fb). White solid: mp 155–156 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.25 (s, 1H, ArH), 7.79–7.71 (m, 2H, ArH), 7.60–7.57 (m, 1H, ArH), 7.50–7.39 (m, 3H, ArH), 7.29–7.26 (m, 1H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ 190.7, 157.4, 153.9, 145.3, 137.7, 136.8, 132.6, 131.9, 130.1, 129.9, 127.3, 127.2, 119.8, 118.6, 117.4. IR (KBr, cm⁻¹): 3080, 2925, 1738, 1656, 1600, 1546, 1468, 1230, 1154. ESI MS (m/z): 363 (M⁺+1); Anal. Calcd for C₁₆H₈BrClO₃: C, 52.85; H, 2.22. Found: C, 52.77; H, 2.11.

3-(2-Chlorobenzoyl)-8-methoxychromen-2-one (10fc). White solid: mp 142–143 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.33 (s, 1H, ArH), 7.57 (d, J = 7.5 Hz, 1H, ArH), 7.45–7.36 (m, 3H, ArH), 7.30–7.18 (m, 3H, ArH), 3.98 (s, 3H, OCH₃). ¹³C NMR (75 MHz, CDCl₃): δ 191.1, 157.4, 147.2, 147.0, 144.8, 137.9, 132.3, 131.5, 130.0, 129.8, 127.0, 126.3, 124.7, 120.9, 118.8, 115.8, 56.2. IR (KBr, cm⁻¹): 2935, 1757, 1719, 1674, 1607, 1570, 1472, 1279, 1102. ESI MS (m/z): 315 (M⁺+1); Anal. Calcd for C₁₇H₁₁ClO₄: C, 64.88; H, 3.52. Found: C, 64.72; H, 3.38.

3-(Biphenyl-4-carbonyl)-6-bromochromen-2-one (10gb). White solid: mp 205–206 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.99–7.93 (m, 3H, ArH), 7.74–7.61 (m, 6H, ArH), 7.47–7.43 (m, 2H, ArH), 7.32–7.25 (m, 2H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ 190.6, 157.8, 153.4, 146.7, 143.6, 139.6, 136.2, 134.5, 131.2, 130.2, 128.9, 128.4, 128.2, 127.3, 119.6, 118.6, 117.5. IR (KBr, cm⁻¹): 3048, 2922, 1724, 1653, 1601, 1555, 1511, 1475, 1235. ESI MS (m/z): 405 (M⁺+1); Anal. Calcd for C₂₂H₁₃BrO₃: C, 65.20; H, 3.23. Found: C, 65.08; H, 3.49.

3-(Biphenyl-4-carbonyl)-8-ethoxychromen-2-one (10ge). White solid: mp 178–179 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.09 (s, 1H, ArH), 7.96 (d, J = 8.4 Hz, 2H, ArH), 7.69–7.61 (m, 4H, ArH), 7.49–7.37 (m, 3H, ArH), 7.29–7.15 (m, 3H, ArH), 4.22 (q, J = 7.2 Hz, 2H, OCH₂), 1.55 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (75 MHz, CDCl₃): δ 191.2, 158.1, 146.6, 146.5, 145.7, 144.6, 139.7, 134.8, 130.2, 128.9, 128.3, 127.3, 127.2, 124.8, 120.2, 118.9, 116.3, 65.0, 14.7. IR (KBr, cm⁻¹): 2977, 1717, 1658, 1604, 1570, 1466, 1399, 1240, 1182. ESI MS (m/z): 371 (M⁺+1); Anal. Calcd for C₂₄H₁₈O₄: C, 77.82; H, 4.90. Found: C, 77.60; H, 4.71.

3-(Biphenyl-4-carbonyl)-8-phenylchromen-2-one (10gf). White solid: mp 192–193 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.16 (s, 1H, ArH), 7.97 (d, J = 8.4 Hz, 2H, ArH), 7.71–7.59 (m, 8H, ArH), 7.52–7.40 (m, 7H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ 191.1, 158.1, 151.5, 146.5, 145.7, 139.7, 135.0, 134.8, 134.7, 130.4, 130.2, 129.4, 128.9, 128.5, 128.4, 128.3, 128.2, 127.3, 127.2, 127.0, 124.9, 118.6. IR (KBr, cm⁻¹): 3063, 2921, 1717, 1654, 1599, 1455, 1242, 1169. ESI MS (m/z): 403 (M⁺+1); Anal. Calcd for C₂₈H₁₈O₃: C, 83.57; H, 4.51. Found: C, 83.41; H, 4.38.

3-(Furan-2-carbonyl)-chromen-2-one (10ha). White solid: mp 159–160 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.16 (s, 1H, ArH), 7.67–7.60 (m, 3H, ArH), 7.41–7.32 (m, 3H, ArH), 6.61-6-60 (m, 1H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ 177.9, 158.0, 154.6, 151.6, 147.7, 145.5, 133.7, 129.2, 126.1, 124.9, 120.7, 118.0, 116.8, 112.7. IR (KBr, cm⁻¹): 3109, 2925, 1719, 1648, 1606, 1564, 1457, 1389, 1173. ESI MS (m/z): 241 (M⁺+1); Anal. Calcd for C₁₄H₈O₄: C, 70.00; H, 3.36. Found: C, 70.32; H, 3.06.

6-Bromo-3-(furan-2-carbonyl)-chromen-2-one (10hb). White solid: mp 191–192 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.05 (s, 1H, ArH), 7.74–7.67 (m, 3H, ArH), 7.36 (d, J = 3.9 Hz, 1H, ArH), 7.30–7.25 (m, 1H, ArH), 6.62 (dd, J = 3.6, 1.2 Hz, 1H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ 177.4, 157.2, 153.4, 151.5, 147.8, 143.8, 136.3, 131.3, 127.1, 120.8, 119.5, 118.6, 117.4, 112.8. IR (KBr, cm⁻¹): 3105, 2932, 1724, 1644, 1604, 1560, 1459, 1359, 1241, 1180. ESI MS (m/z): 319 (M⁺+1); Anal. Calcd for C₁₄H₇BrO₄: C, 52.69; H, 2.21. Found: C, 52.44; H, 2.39.

3-(Furan-2-carbonyl)-8-methoxychromen-2-one (10hc). White solid: mp 138–139 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.14 (s, 1H, ArH), 7.66 (s, 1H, ArH), 7.35 (d, J = 3.3 Hz, 1H, ArH), 7.30–7.16 (m, 3H, ArH), 6.60–6.59 (m, 1H, ArH), 3.99 (s, 3H, OCH₃). ¹³C NMR (75 MHz, CDCl₃): δ 178.0, 157.5, 151.6, 147.7, 147.1, 145.7, 126.4, 124.8, 120.8, 120.4, 118.6, 115.3, 112.7, 56.3. IR (KBr, cm⁻¹): 2924, 2854, 1720, 1648, 1608, 1465, 1277, 1184. ESI MS (m/z): 271 (M⁺+1); Anal. Calcd for C₁₅H₁₀O₅: C, 66.67; H, 3.73. Found: C, 66.51; H, 3.49.

6-Bromo-3-(thiophene-2-carbonyl)-chromen-2-one (10ib). White solid: mp 201–202 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.99 (s, 1H, ArH), 7.79 (d, J = 4.8 Hz, 1H, ArH), 7.74–7.70 (m, 3H, ArH), 7.31–7.25 (m, 1H, ArH), 7.18–7.15 (m, 1H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ 182.3, 157.5, 153.3, 143.0, 142.5, 136.3, 136.0, 135.2, 131.2, 128.4, 127.8, 119.4, 118.6, 117.5. IR (KBr, cm⁻¹): 2926, 1721, 1631, 1566, 1410, 1239, 1210, 1160. ESI MS (m/z): 335 (M⁺+1); Anal. Calcd for C₁₄H₇BrO₃S: C, 50.17; H, 2.11. Found: C, 50.29; H, 2.23.

8-Phenyl-3-(thiophene-2-carbonyl)-chromen-2-one (10if). White solid: mp 181–182 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.15 (s, 1H, ArH), 7.76–7.68 (m, 3H, ArH), 7.64–7.57 (m, 3H, ArH), 7.52–7.39 (m, 4H, ArH), 7.16–7.13 (m, 1H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ 182.9, 157.8, 151.4, 145.1, 142.8, 135.6, 135.2, 135.0, 134.8, 130.4, 129.4, 128.5, 128.4, 128.3, 128.2, 126.7, 124.9, 118.4. IR (KBr, cm⁻¹): 2922, 1719, 1632, 1597, 1411, 1242, 1159. ESI MS (m/z): 333 (M⁺+1); Anal. Calcd for C₂₀H₁₂O₃S: C, 72.27; H, 3.64. Found: C, 72.39; H, 3.77.

6-Bromo-3-(Ferrocene-2-carbonyl)-chromen-2-one (10jb). Red solid: mp 181–182 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.86 (s, 1H, ArH), 7.71–7.69 (m, 2H, ArH), 7.30–7.27 (m, 1H, ArH), 4.84 (s, 2H, H_cp), 4.66 (s, 2H, H_cp), 4.29 (s, 5H, H_cp). ¹³C NMR (75 MHz, CDCl₃): δ 193.5, 157.3, 153.1, 140.1, 135.7, 130.9, 128.9, 119.5, 118.5, 117.3, 73.6, 71.6, 70.8. IR (KBr, cm⁻¹): 3088, 2923, 1727, 1641, 1606, 1553, 1451, 1019. ESI MS (m/z): 437 (M⁺+1); Anal. Calcd for C₂₀H₁₃BrFeO₃: C, 54.96; H, 3.00. Found: C, 55.12; H, 2.96.

3-(Ferrocene-2-carbonyl)-8-methoxychromen-2-one (10jc). Red solid: mp 178–179 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.94 (s, 1H, ArH), 7.29–7.25 (m, 1H, ArH), 7.17–7.13 (m, 2H, ArH), 4.85 (s, 2H, H_cp), 4.63 (s, 2H, H_cp), 4.27 (s, 5H, H_cp), 4.00 (s, 3H, OCH₃). ¹³C NMR (75 MHz, CDCl₃): δ 194.0, 157.4, 147.1, 144.0, 141.9, 128.2, 124.6, 120.0, 118.6, 114.7, 73.3, 70.9, 70.4, 56.3. IR (KBr, cm⁻¹): 3080, 2925, 1737, 1656, 1608, 1572, 1472, 1360, 1275, 1175. ESI MS (m/z): 389 (M⁺+1); Anal. Calcd for C₂₁H₁₆FeO₄: C, 64.97; H, 4.15. Found: C, 64.78; H, 4.39.

3-(Ferrocene-2-carbonyl)-6-nitrochromen-2-one (10jd). Red solid: mp 222–223 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.51–8.47 (m, 2H, ArH), 7.99 (s, 1H, ArH), 7.53 (d, J = 9.0 Hz, 1H, ArH), 4.85 (s, 2H, H_cp), 4.70 (s, 2H, H_cp), 4.31 (s, 5H, H_cp). ¹³C NMR (75 MHz, CDCl₃): δ 192.8, 157.5, 156.4, 144.2, 139.9, 129.9, 127.5, 124.4, 118.2, 118.1, 73.9, 70.8, 70.6. IR (KBr, cm⁻¹): 3052, 2923, 1741, 1632, 1576, 1524, 1343, 1168. ESI MS (m/z): 404 (M⁺+1); Anal. Calcd for C₂₀H₁₃FeNO₅: C, 59.58; H, 3.25; N, 3.47. Found: C, 59.87; H, 3.09; N, 3.19.

8-Ethoxy-3-(Ferrocene-2-carbonyl)-chromen-2-one (10je). Red solid: mp 145–146 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.94 (s, 1H, ArH), 7.21–7.11 (m, 3H, ArH), 4.86 (s, 2H, H_cp), 4.63 (s, 2H, H_cp), 4.28 (s, 5H, H_cp), 4.23 (q, J = 6.9, 2H, OCH₂), 1.53 (t, J = 6.9 Hz, 3H, CH₃). ¹³C NMR (75 MHz, CDCl₃): δ 194.1, 157.6, 146.5, 144.2, 142.0, 128.1, 124.6, 119.9, 118.7, 115.9, 73.3, 70.9, 70.4, 65.0, 14.7. IR (KBr, cm⁻¹): 3095, 2925, 1706, 1649, 1612, 1465, 1273, 1173, 1091. ESI MS (m/z): 403 (M⁺+1); Anal. Calcd for C₂₂H₁₈FeO₄: C, 65.69; H, 4.51. Found: C, 65.82; H, 4.39.

6-Bromo-3-(2,2-dimethylpropionyl)-chromen-2-one (10kb). White solid: mp 130–131 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.68–7.65 (m, 2H, ArH), 7.52 (s, 1H, ArH), 7.26 (s, 1H, ArH), 1.30 (s, 9H, 3 × CH₃). ¹³C NMR (75 MHz, CDCl₃): δ 207.3, 157.5, 152.7, 138.9, 135.3, 130.7, 130.6, 119.4, 118.5, 117.4, 45.0, 26.4. IR (KBr, cm⁻¹): 3052, 2952, 1726, 1681, 1554, 1477, 1182. ESI MS: m/z = 309 (M⁺+1); Anal. Calcd for C₁₄H₁₃BrO₃: C, 54.39; H, 4.24. Found: C, 54.07; H, 4.47.

3-(2,2-Dimethylpropionyl)-8-ethoxychromen-2-one (10ke). White solid: mp 65–66 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.58 (s, 1H, ArH), 7.24–7.19 (m, 1H, ArH), 7.12–7.05 (m, 2H, ArH), 4.13 (q, J = 6.9 Hz, 2H, OCH₂), 1.51 (t, J = 6.9 Hz, 3H, CH₃), 1.31 (s, 9H, 3 × CH₃). ¹³C NMR (75 MHz, CDCl₃): δ 208.1, 157.8, 146.4, 143.8, 140.8, 129.8, 124.6, 119.6, 118.6, 115.5, 64.9, 44.9, 26.5, 14.6. IR (KBr, cm⁻¹): 3047, 2967, 1718, 1665, 1559, 1489, 1156. ESI MS: m/z = 275 (M⁺+1); Anal. Calcd for C₁₆H₁₈O₄: C, 70.06; H, 6.61. Found: C, 70.35; H, 6.24.

3-(2,2-Dimethylpropionyl)-8-phenylchromen-2-one (10kf). White solid: mp 87–88 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.67 (s, 1H, ArH), 7.64–7.59 (m, 2H, ArH), 7.50–7.35 (m, 6H, ArH), 1.31 (s, 9H, 3 × CH₃). ¹³C NMR (75 MHz, CDCl₃): δ 207.9, 157.8, 150.7, 141.2, 135.1, 133.8, 130.2, 129.6, 129.4, 128.5, 128.1, 127.7, 124.7, 118.3, 45.0, 26.5. IR (KBr, cm⁻¹): 2918, 2850, 1703, 1655, 1458, 1169. ESI MS: m/z = 307 (M⁺+1); Anal. Calcd for C₂₀H₁₈O₃: C, 78.41; H, 5.92. Found: C, 78.58; H, 5.79.

3-(Biphenyl-4-carbonyl)-benzo[f]chromen-2-one (12g). White solid: mp 233–234 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.96 (s, 1H, ArH), 8.29 (d, J = 8.1 Hz, 1H, ArH), 8.12 (d, J = 9.0 Hz, 1H, ArH), 8.02–7.95 (m, 3H, ArH), 7.76–7.63 (m, 6H, ArH), 7.60–7.38 (m, 4H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ 191.6, 158.6, 155.4, 146.4, 141.8, 139.8, 135.3, 135.1, 130.3, 130.2, 129.4, 129.2, 129.0, 128.9, 128.3, 127.3, 127.2, 126.5, 125.4, 121.5, 116.7, 112.7. IR (KBr, cm⁻¹): 2927, 1716, 1656, 1603, 1565, 1262, 1210. ESI MS (m/z): 377 (M⁺+1); Anal. Calcd for C₂₆H₁₆O₃: C, 82.96; H, 4.28. Found: C, 82.63; H, 4.57.

3-(Ferrocene-2-carbonyl)-benzo[f]chromen-2-one (12j). Red solid: mp 194–195 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.79 (s, 1H, ArH), 8.26 (d, J = 8.4 Hz, 1H, ArH), 8.09 (d, J = 9.0 Hz, 1H, ArH), 7.96 (d, J = 7.8 Hz, 1H, ArH), 7.75–7.70 (m, 1H, ArH), 7.64–7.51 (m, 2H, ArH), 4.93 (s, 2H, H_cp), 4.67 (s, 2H, H_cp), 4.31 (s, 5H, H_cp). ¹³C NMR (75 MHz, CDCl₃): δ 194.3, 154.7, 138.0, 134.7, 130.3, 129.3, 129.2, 128.8, 126.6, 126.4, 121.3, 116.8, 112.4, 73.4, 71.0, 70.5. IR (KBr, cm⁻¹): 3061, 2954, 1718, 1635, 1543, 1461, 1382. ESI MS (m/z): 409 (M⁺+1); Anal. Calcd for C₂₄H₁₆FeO₃: C, 70.61; H, 3.95. Found: C, 70.52; H, 4.32.

3-(2,2-Dimethylpropionyl)-benzo[f]chromen-2-one (12k). Yellowish solid: mp 133–134 °C. ¹H NMR (300 MHz, CDCl₃): δ 8.46 (s, 1H, ArH), 8.23 (d, J = 8.7 Hz, 1H, ArH), 8.05 (d, J = 9.0 Hz, 1H, ArH), 7.93 (d, J = 8.1 Hz, 1H, ArH), 7.74–7.69 (m, 1H, ArH), 7.62–7.57 (m, 1H, ArH), 7.48 (d, J = 9.0 Hz, 1H, ArH), 1.38 (s, 9H, 3 × CH₃). ¹³C NMR (75 MHz, CDCl₃): δ 205.8, 158.2, 154.2, 137.4, 134.2, 130.2, 129.1, 129.0, 128.6, 128.3, 126.3, 121.3, 116.6, 112.2, 44.9, 26.6. IR (KBr, cm⁻¹): 3072, 2973, 1710, 1568, 1460, 1210, 1181. ESI MS (m/z): 281 (M⁺+1); Anal. Calcd for C₁₈H₁₆O₃: C, 77.12; H, 5.75. Found: C, 77.43; H, 5.49.

Acknowledgements

This work was carried out under financial support from Council of Scientific and Industrial Research (Grant 01(2260)/08/EMR-II) and Department of Science and Technology (Grant SR/S1/OC-66/2009), New Delhi. R.K.V. and G.S. are grateful to CSIR, New Delhi for SRF and JRF, respectively and G.K.V. is thankful to University Grants Commission (UGC), New Delhi for junior research fellowship.

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Footnote

† Electronic supplementary information (ESI) available: detailed experimental and spectral data, crystallographic data, and original ¹H and ¹³C NMR spectrum of all compounds. CCDC reference numbers 805566 and 805567. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2ra00987k

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