An effective method for the preparation of optically active polyoxy 8-membered ring enone corresponding to the B ring of taxol

An effective method for the preparation of 8-membered ring enone 1 in suffi cient quantities was developed. First, optically active trialkoxyaldehyde 3 was prepared by diastereoselective dihydroxylation of olefin 7 derived fro m D-pantolactone. Secondly, 8-chloro-7-oxoaldehydes 20 alpha,beta were newl y synthesized by the following reactions: namely, MgBr2. OEt2-mediated dias tereoselective aldol reaction of the aldehyde 3 with ketene (trimethylsilyl ) acetal 15, direct 1,1-dichloroethylation of ester 17 with 1,1-dichloroeth yllithium, and partial dehalogenation of the resulting oc,a-dichloroethyl k etone 18 with (Bu3SnH)-Bu-n. Lastly, the chiral 8-chloro-7-oxoaldehydes 20 alpha,beta were converted to the 8-membered ring enone 1 by SmI2-mediated a ldol cyclization.