Cyclisation of polyenic β-keto suiphoxides. A novel route to optically active intermediates for cyclic terpenoid synthesis

Abstract

Optically active polyenic β-keto sulphoxides 4 and 5 undergo a cyclisation mediated by SnCl₄ to give easily separable diastereoisomeric dihydropyran derivatives 6a,b and 10a,b, respectively; the crystalline stereoisomers of which can be converted into (+)-dihydroacitinidiolide 7 and (–)-norambreinolide 11.