An Efficient FeCl₃-Catalyzed Condensation of Thiols with 1,3-Dicarbonyl Compounds under Solvent-Free Conditions

Abstract

A practical and environmentally friendly method has been developed for the synthesis of thiol-substituted cyclohex-2-enones using a FeCl₃-catalyzed condensation of cyclic 1,3-dicarbonyl compounds and aromatic/aliphatic thiols under solvent-free conditions at ambient temperature.

Key words

condensation - thiols - green chemistry - Lewis acids - iron

• References and Notes

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• 16 General Experimental Procedure The requisite thiol 1 (1.2 mmol), cyclic 1,3-dione 2 (1mmol), and anhydrous FeCl₃ (15 mol%) were placed in a round-bottomed flask and then stirred at r.t. to 50 °C for the specified time (Table 2). After completion of the reaction (as monitored by TLC), H₂O was added to the reaction mixture, and then it was extracted with EtOAc (3 × 10 mL). The combined organic phases were washed with brine, dried over anhydrous Na₂SO₄, filtered, and concentrated on a rotary evaporator. The crude product was purified by column chromatography using EtOAc–hexane as eluent to afford pure product 3. Representative Data 5,5-Dimethyl-3-(phenylthio)cyclohex-2-enone (3a) Solid; mp 50–52 °C (lit.¹⁷ mp 50–51 °C). FTIR (KBr): 2955, 2868, 1662, 1574, 1454, 1305, 1279, 1239, 1021, 716 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.07 (s, 6 H), 2.22 (s, 2 H), 2.39 (s, 2 H), 5.47 (s, 1 H), 7.40–7.48 (m, 5 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 27.8, 34.1, 43.7, 50.9, 119.6, 127.9, 129.7, 130.0, 135.3, 164.8, 196.1 ppm. 3-(Phenylthio)cyclohex-2-enone (3h) Solid; mp 44–45 °C (lit.¹⁸ mp 43–44 °C). FTIR (KBr): 2950, 2868, 1655, 1580, 1454, 1310, 1280, 1240, 1020, 710 cm^–1. ¹H-NMR (300 MHz, CDCl₃): δ = 1.99–2.03 (m, 2 H), 2.32–2.36 (m, 2 H), 2.48–2.51 (m, 2 H), 5.47 (s, 1 H), 7.38–7.47 (m, 5 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 22.8, 29.8, 36.8, 120.5, 127.6, 129.5, 129.8, 135.1, 166.5, 195.6 ppm.
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