SYNTHETIC STUDIES ON THE RHIZOXINS .1. 2 STEREOSELECTIVE ROUTES TO A FUNCTIONALIZED C1-C-9 SUBUNIT

Two syntheses of a potential C1-C-9 subunit of rhizoxin are described. In the first, chelation-controlled allylstannane addition to optically pure aldehyde 3, conversion to unsaturated ester 7, and stereoselective intramolecular Michael addition is used to establish the relative stereochemistry at C-7 and C-8 (rhizoxin numbering). In the second, an Evans aldol condensation is used to control absolute and relative stereochemistry at these centers. Both approaches use thermodynamic control to establish the correct stereochemistry at C5.