An unusual reversal of stereoselectivity in a boron mediated aldol reaction:: Enantioselective synthesis of the C1-C6 segment of the epothilones

Enantioselective syntheses of differentially protected C-1-C-6 fragments, (3S)-3-hydroxy-4,4-dimethyl-5-oxoheptanoic acid 4, (5S)-7-[1,1-bis(mechylethyl)-2-methyl-1 -silapropoxy]-5-hydroxy-4,4-dimethylheptan-3-one 5 and (4S)-2-(2,2-dimethyl-1,3-dioxan-4-yl)-2-methylpentan-3-one 23, common to both epothilones A and B, are reported. (C) 2000 Elsevier Science Ltd. All rights reserved.