Stereoselective Aldol Condensations via Boron Enolates. The Syntheses of (+)-Prelog-Djerassi Lactone and (+)-Tylonolide
<p>The use of boron enolates of chiral N-acyl oxazolidinones i and ii in highly stereoselective aldol condensations is described. Mild base hydrolysis of the products affords optically pure erythro β-hydroxy acids and the chiral auxiliary, which can be reconverted into i or ii in one step.<...