Ring contraction of 3,6-Dihydro-2H-thiopyrans to thiolanes by an lodo-oxyacylation reaction

Abstract

Reaction of functionalized 3,6-dihydro-2H-thiopyrans with N-iodosuccinimide in the presence of carboxylic acids results in the stereospecific formation of poly-functionalised thiolanes in good yield. The formation of these thiolanes is believed to proceed through either a nucleophilic or an electrophilic pathway leading to 4,5-cis-substituted derivatives. The use of unsymmetrical 2,2-substituted 3,6-dihydro-2H-thiopyrans gave mixtures of isomers that could be separated in several cases. From a 3-substituted thiopyran a 2,2,3,4,5-pentasubstituted thiolane was obtained. Attempts to use alcohols as external nucleophiles were unsuccessful with NIS, NBS, and N-bromoacetamide. Iodo-azidination with in situ generated IN3 was also unsuccessful. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).