Oppolzer sultam directed aldol as a key step for the stereoselective syntheses of antitumor antibiotic belactosin C and its synthetic congeners.

[reaction: see text] An efficient protocol has been developed using D-(2R)-Oppolzer sultam as a chiral auxiliary for generating anti/syn diastereomers with high enantiopurity and utilized in the efficient synthesis of natural product belactosin C and their synthetic congeners. It has been observed that a variation in the stoichiometry of the Lewis acid led to a difference in anti/syn selectivity.