Stereocontrolled synthesis of E-homoallylic sulfides with 1,4,5 related chiral centres using the [2,3] sigmatropic rearrangement of sulfonium ylides

Abstract

E-Homoallylic sulfides with 1,4,5 related chiral centres have been synthesised in a stereocontrolled way. An aldol condensation sets up the stereochemistry. Lactonisation with 1,2 arylsulfanyl migration followed by reduction and sulfur-assisted dehydration converts the aldols stereospecifically into allylic sulfides with 1,2 related chiral centres. Sulfonium salts are generated from the allylic sulfides at low temperature, and are deprotonated to give sulfonium ylides which undergo [2,3] sigmatropic rearrangement in good yield to give E-homoallylic sulfides with 1,4,5 related chiral centres. The 1,4 relative stereochemistry results from stereospecific chiral transfer and is directly related to the allylic sulfide 1,2 relative stereochemistry. High 4,5 diastereoselectivity is also observed. An explanation for the observed stereoselectivity is provided.