Synthesis and Conformation of 4,4,5,5-Tetramethyl-1,2-dithiane Mono-S-oxide

Article abstract of DOI:10.1021/jo00249a038

The synthesis of the title compound (6), an interesting subject for the study of anomeric and other conformational effects, was attained from ethyl isobutyrate in eight steps, with an overall yield of 11percent.The synthetic route described herein involved the crucial displacement of both neopentylic tosylate groups in 2,2,3,3-tetramethyl-1,4-butanediol ditosylate; while several standard procedures led to the formation of unexpected products, purified potassium thioacetate in hexamethylphosphoramide afforded the required dithioacetate derivative.The mechanistic implications of the well- and bad-behaved reactions are discussed.From the results of variable-temperature NMR experiments it is concluded that the axial conformer of 6 dominates the equilibrium to such an extent that no contribution of the equatorial isomer is recorded.This result sudggests a ΔG⁰ <*> 3.0 kcal/mol for the conformational equilibrium of the parent 1,2-dithiane mono-S-oxide.