Remarkable long range effects on the diastereoface selectivity in an aldolcondensation

The stereochemical results in an aldol reaction between the enolate 2 and v arious alpha-methyl aldehydes indicates a stabilizing through space interac tion between C-4-C-5 unsaturation and the formyl group. This interaction le ads to a reaction conformation which favors a C-7-C-8 (epothilone numbering ) anti-relationship in the aldol products. Included is an extensive study t hat identifies steric and electronic effects of various alpha-methyl aldehy des in the aldol diastereoselection. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.