Cyclization of γδ-unsaturated sulphenic acids to give thietan 1-oxide derivatives. Crystal structure of rel-(1R,2S,3R,4R)-3-hexyl-2-hydroxymethyl-4-methylthietan 1-oxide

Abstract

erythro- and threo-2-t-Butylthio-3-vinylnonan-1-ol have been prepared by Claisen rearrangement of the silylketen acetals derived from (E)-non-2-enyl t-butylthioacetate followed by reduction with lithium aluminium hydride. The sulphur function influenced the stereoselectivity of formation of the silylketen acetals which, in turn, determined the ratio of diastereoisomeric products obtained in the rearrangement. Thermolysis of erythro-2-t-butylsulphinyl-3-vinylnonan-l-ol at 140 °C for 5 min gave erythro-1-(hydroxymethyl)-2-vinyloctanesulphenic acid which cyclized spontaneously to a mixture of rel-(1R,2R,3S,4R)- and rel-(1R,2S,3R,4R)-3-hexyl-2-(hydroxymethyl)-4-methylthietan 1-oxide. threo-2-Butylsulphinyl-3-vinylnonan-1-ol under the same conditions gave a mixture of rel-(1R,2R,3R,4R)- and rel-(1R,2S,3S,4R)-3-hexyl-2-(hydroxymethyl)-4-methylthietan 1-oxide. Allocations of configuration to these thietan 1-oxide derivatives based on transition-state considerations have been substantiated by a determination of the crystal structure of the rel-(1R,2S,3R,4R)-isomer and by n.m.r. spectroscopy, which also led to tentative assignments of conformation.