Synthesis of 2H-Thiopyrans via Multicomponent Reactions in Water

Abstract

A series of 2H-thiopyran derivatives has been synthesized via one-pot multicomponent reactions of dialkyl acetylenedicarboxylates, arylisothiocyanates, and α-bromoketones in the presence of triphenylphosphine in water under both conventional heating and microwave irradiation. The yields obtained under ­microwave irradiation were superior and the reaction times were ­reduced in comparison with conventional heating.

Key words

2H-thiopyran - triphenylphosphine - α-bromoketone - microwave irradiation - arylisothiocyanate

• References and Notes

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• 11 General Procedure for the Preparation of Compounds 5 To a magnetically stirred solution of α-bromoketone (2 mmol) in H₂O (10 mL) was added Ph₃P (2 mmol) at 70 °C under microwave irradiation (MICROSYNTH, Mylestone Company). After 45 min, Et₃N (2 mmol) and dialkyl acetylenedicarboxylate 2 (2 mmol) were added to this mixture. After 15 min the aryl isothiocyanate was added, and the reaction mixture was stirred for 4 h at 70 °C under microwave irradiation. After completion of reaction (monitoring by TLC), the reaction mixture was filtered and the solid residue was washed with cold Et₂O to afford 5. Dimethyl 6-Phenyl-2-(phenylimino)-2H-thiopyran-3,4-dicarboxylate (5a) White powder; mp 125–128 °C, 0.61 g, yield 80%. IR (KBr): ν_max = 1738, 1735, 1694, 1587, 1378, 1298, 1129 cm^–1. Anal. Calcd for C₂₁H₁₇NO₄S (379.43): C, 66.48; H, 4.52; N, 3.69. Found: C, 66.54; H, 4.65; N, 3.78. ¹H NMR (500 MHz, CDCl₃): δ = 3.75 (3 H, s, MeO), 3.82 (3 H, s, MeO), 7.10 (1 H, s, CH), 7.34 (3 H, t, ³ J = 7.4 Hz, 3 CH), 7.54 (3 H, t, ³ J = 7.4 Hz, 3 CH), 7.67 (2 H, d, ³ J = 7.5 Hz, CH), 7.86 (2 H, d, ³ J = 7.6 Hz, 2 CH) ppm. ¹³C NMR (125.7 MHz, CDCl₃): δ = 51.7 (MeO), 52.3 (MeO), 123.4 (2 CH), 123.8 (CH), 124.2 (CH), 126.3 (C), 127.5 (2 CH), 128.0 (CH), 128.7 (2 CH), 130.4 (2 CH), 136.8 (C), 148.2 (C), 151.2 (C), 154.3 (C), 167.2 (C=O), 171.4 (C=O) ppm. MS: m/z (%): 379 (15) [M⁺], 348 (56), 77 (100), 31 (100).
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