Montmorillonite K-10 Clay as an Efficient Solid Catalyst for Chemoselective Protection of Carbonyl Compounds as Oxathiolanes with 2-Mercaptoethanol

Abstract

Montmorillonite K-10 clay has been found to be a mild and efficient solid catalyst for the protection of a variety of carbonyl compounds, such as oxathiolanes, with 2-mercaptoethanol in good to excellent yields. In addition, by using this catalyst, high chemoselective protection of aldehydes in presence of ketones has been achieved.

carbonyl compounds - 2-mercaptoethanol - montmorillonite K-10 - chemoselective - oxathiolanes

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Typical Experimental Procedure: To a stirred mixture of benzaldehyde (0.2 g, 1.9 mmol) and 2-mercaptoethanol (0.195 g, 2.5 mmol) in CH₂Cl₂ (5 mL) was added mont-morillonite K-10 clay (0.4 g, two times the mass of the substrate). The mixture was stirred at r.t. for 0.5 h. The end of the reaction was monitored by TLC (silica gel plate; 1:12 EtOAc-hexane). After completion, the reaction mixture was filtered off and washed with CH₂Cl₂ (3 × 5 mL). The filtrate was dried (Na₂SO₄) and evaporation of organic solvent afforded crude product. The crude product was purified by preparative TLC over silica gel (1:12 EtOAc-hexane as a solvent system) to afford pure 2-phenyl-1,3-oxathiolane (0.271 g, 86%, entry 4 in Table [1] ). All the data (IR, ¹H NMR and mass spectra) recorded are identical with the authentic samples and the reported methods.
Spectral data for compound 4: IR (KBr): ν_max = 1069 (C-O-C), 681 (C-S-C) cm^-1. ¹H NMR (300 MHz, CDCl₃): δ = 3.15-3.31 (m, 2 H, -S-CH₂-), 3.87-3.94 (m, 1 H, -O-CH₂-), 4.50-4.53 (m, 1 H), 6.02 (s, 1 H, -O-CH-S), 7.29-7.40 (m, 3 H), 7.44-7.48 (m, 2 H) ppm. ¹³C NMR (125 MHz, CDCl₃): δ = 138.99, 136.32, 129.53, 126.76, 87.17, 71.93, 34.10 ppm.