Highly diastereoselective aldol reactions of cobalt-complexed and uncomplexed propynals with O-silyl ketene O,S-ketals: highly stereoselective divergent formal syntheses of the β-lactam antibiotics (±)-PS-5 and (±)-epi-PS-5

Abstract

Treatment of a cobalt-complexed propynal derived from 3-trimethylsilylprop-2-ynal with O-silyl ketene O,S-ketals afforded the syn-aldol products exclusively, whereas the uncomplexed substrate 3-trimethylsilylprop-2-ynal provided the anti-ones exclusively or in a highly diastereoselective manner. These newly developed aldol reactions could be successfully applied to highly stereoselective formal syntheses of the carbapenem antibiotics (±)-PS-5 and (±)-6-epi-PS-5.