Phase-Transfer-Catalyzed Asymmetric Alkylation of alpha-Benzoyloxy-beta-keto Esters: Stereoselective Construction of Congested 2,3-Dihydroxycarboxylic Acid Esters

Highly enantioselective phase-transfer-catalyzed alkylation of tert-butyl 2-benzoyloxy-3-oxobutanoate was realized by the use of an N-spiro chiral quaternary ammonium salt, as a complementary approach to the asymmetric hydroxylation of alpha-alkyl-beta-keto esters. The synthetic utility of the alkylated compounds is highlighted by the diastereoselective reduction and alkylation of the remaining ketone moiety to give various enantiomerically enriched congested 2,3-dihydroxy-carboxylic acid esters.