Efficient One-Pot Synthesis of Unsymmetrical 2-Thioparabanic Acids from Oxalyl Chloride, Benzoyl Isothiocyanate, and Primary Amines

Abstract

An efficient synthesis of unsymmetrical 2-thioparabanic acids is described via a three-component reaction between benzoyl isothiocyanate and primary amines in the presence of oxalyl chloride.

Key word

oxalyl chloride - primary amines - 2-thioparabanic acid - multicomponent reaction

References and Notes

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16

1-Benzyl-2-thioxodihydro-1 H -imidazole-4,5-dione (4a) To a stirred solution of benzoyl isothiocyanate (0.32 g, 2 mmol) and benzylamine (0.20 g, 2 mmol) in CH₂Cl₂ (10 mL) was added oxalyl chloride (0.25 g, 2 mmol) at r.t. The reaction mixture was then stirred for 12 h. The solvent was removed under reduced pressure and the viscous residue was purified by flash column chromatography on SiO₂ (Merck 230-400 mesh) using hexane-EtOAc as eluent to give 4a as yellow powder; mp 151-153 °C, yield 0.30 g (70%). IR (KBr): ν_max = 3220, 1764, 1735, 1666, 1441, 1340 cm^-1. ¹H NMR (500 MHz, CDCl₃): δ = 5.10 (2 H, s, NCH₂), 7.28 (1 H, d, ³ J = 7.1 Hz, CH), 7.32 (2 H, t, ³ J = 7.6 Hz, CH), 7.41 (2 H, d, ³ J = 7.3 Hz, CH), 11.71 (1 H, br s, NH) ppm. ¹³C NMR (125 MHz, CDCl₃): δ = 45.0 (NCH₂), 128.6 (CH), 129.0 (CH), 129.2 (CH), 136.2 (CH), 156.8 (C=O), 157.3 (C=O), 182.7 (C=S) ppm. MS: m/z (%) = 222 (4) [M⁺ + 2], 221 (10) [M⁺ + 1], 220 (64) [M⁺], 91 (26), 77 (60), 59 (20), 45 (60). Anal. Calcd (%) for C₁₀H₈N₂O₂S (220.24): C, 54.53; H, 3.66; N, 12.72. Found: C, 54.41; H, 3.70; N, 12.65.