Total synthesis of (-)-coriolin

An efficient synthetic method for (-)-coriolin has been developed on the ba sis of a [3+2] cycloaddition reaction of a 1-( methylthio)-2-siloxyallyl ca tionic species and vinylsulfides. An enantiomerically pure C-ring unit was prepared through optical resolution of five-membered allyl ester 6b using a lipase. The first [3+2] cycloaddition reaction of C-ring unit (S)-7 gave b icyclic ketones 8 and 9, which were easily converted into vinyl sulfide 11. Stereoselective construction of the A-ring was achieved by the second [3+2 ] cycloaddition reaction of the BC-ring unit. New methods for introduction of the oxygen functional groups to the triquinane skeleton were also develo ped for the last stages of the total synthesis. Thus, the C7 hydroxyl group was introduced by epoxidation of dienol silyl ether 17, and stereocontroll ed construction of the spiro epoxide moiety was accomplished on the basis o f a Darzens-type reaction.