Oppolzer Sultam Directed Aldol as a Key Step for the Stereoselective Syntheses of Antitumor Antibiotic Belactosin C and Its Synthetic Congeners^†^,^‡

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.