37 SYNTHETIC STUDIES DIRECTED TOWARD MAYTANSINE
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We have recently developed the heteroconjugate addition and acyclic asymmetric induction aiming at total synthesis of maytansine [1]. Here we describe novel stereocontrolled elaboration of carbon-carbon bonds and functional groups of this molecule. Methyllithium was designed to add to such hetero-olefins as 2 that have substituents with alpher asymmetric center with which the lithium cation can coordinate by chelation so as the methyl anion to add pseudo-intramolecularly. The free hydroxyl cases (in Table 1) showed the best asymmetric induction exceeding 99% threo isomer. Pyranosyl hetero-olefin [12] was prepared from acrolein dimer as racemic-sugar model to look at the asymmetric induction. In cases of the methoxyethyl pyranosides, the addition of methyllithium also underwent perfectly. D-Mannose was converted into the optically active synthetic intermediate (Fig. 8, 9) which corresponds to carbon five through carbon eleven of 1. Further synthetic studies toward 1 will be discussed.
