Compound 11, representing the C(11)-C(20) segment of the macrolide epothilone B (1b) has been prepared using two Wittig reactions and a Sharpless asymmetric epoxidation as the key steps. (C) 1997 Elsevier Science Ltd.
described, starting from optically pure (S)-malic acid and methyl (R)-3-hydroxy-2-methylpropionate. The synthesis is highly convergent by coupling the three fragments C1-C6 (fragment D), C7-C10 (fragment C), and C11-C21 (fragment B). Key steps are two stereoselectiveWittig type olefinations to generate the 12,13- and 16,17-double bonds, an enantioselective Mukaiyama aldol addition to synthesize fragment