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 sufficient quantities was developed. First, optically active trialkoxyaldehyde 3 was prepared by diastereoselective dihydroxylation of olefin 7 derived from D-pantolactone. Secondly, 8-chloro-7-oxoaldehydes 20(alpha),(beta) were newly synthesized by the following reactions: namely, MgBr2·OEt2mediated diastereoselective aldol reaction of the aldehyde 3 with ketene (trimethylsilyl) acetal 15, direct 1,1dichloroethylation of ester 17 with 1,1-dichloroethyllithium, and partial dehalogenation of the resulting (alpha),(alpha)-dichloroethyl ketone 18 with nBu3SnH. Lastly, the chiral 8-chloro-7-oxoaldehydes 20(alpha),(beta) were converted to the 8-membered ring enone 1 by SmI2-mediated aldol cyclization