Further insight into the asymmetric vinylogous Mukaiyama aldol reaction (VMAR); application to the synthesis of the C27-C45 segment of lagunamide A

Two iterative vinylogous Mukaiyama aldol reactions (VMAR) have been applied in order to selectively install three contiguous stereocenters at C37, C38 and C39, of the southern hemisphere of lagunamide A. The VMAR methodology allows straightforward access of enantiomerically pure material of the essential segment via seven steps, and in an overall yield of 34%. The synthesis has an orthogonal protecting group strategy, essential for upcoming synthesis for completion of lagunamide A. We also demonstrate that steric bulk of the chiral oxazolidinone pose certain challenges when employing stereochemically crowded α-substituted aldehydes in various VMAR's. A simple synthesis of the essential (2R,3S)-2-hydroxy-3-methylpentanoic acid fragment via Mitsunobu chemistry was also accomplished and incorporated into the C27-C45 fragment of lagunamide A.

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