CYCLIZATION OF POLYENIC BETA-KETO SULFOXIDES - A NOVEL ROUTE TO OPTICALLY-ACTIVE INTERMEDIATES FOR CYCLIC TERPENOID SYNTHESIS

Optically active polyenic beta-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.