Asymmetric Aldol Reactions

Chiral auxiliary based and organocatalyzed aldol reactions have been used for the asymmetric synthesis of various natural products. These reactions steps have been used in synthesizing γ-butyrolactone containing natural products and their analogs. An asymmetric route for one-pot synthesis of trans- and cis-4,5-disubstituted-γ-butyrolactones via reagent sequence controlled syn- and anti- aldol reactions of N-succinyl-2-oxazolidinone are described. Mechanistic studies are discussed. Using these asymmetric syn- and anti-aldol reactions of chiral N-succinyl-2-oxazolidinones, trans-paraconic acids and cis-paraconic acids are synthesized in both of their enantiomeric forms. Enantioselective one-pot synthesis of β-(hydroxyalkyl)-γ-butyrolactones employing cross-aldol reaction catalyzed by an organocatalyst is described. Efficient routes for the asymmetric synthesis of (–)-enterolactone, natural hydroxyenterolactone and its analog utilizing organocatalytic asymmetric cross-aldol reaction and C-alkylation as the key steps are achieved. Similar routes have provided chiral intermediates, which could be converted to epi-isohydroxymatairesinol and (7ʹR)-7ʹ-hydroxymatairesinol.