Studies on the intramolecular Claisen condensation and related reactions

Abstract: Intramolecular Claisen or Claisen-like condensations of ß-acetoxy esters, amides or imides to ß-keto-5-lactones are described. Two compounds which can give either this reaction or the analogous reaction to y-lactone prefer to give the latter. Highly diastereoselective hydrogenations of enol ether derivatives of ß-keto-6-lactones over Pd are described. A concise synthesis of a natural 5-lactone, (2S,5R)-2- methyl-5-hexanolide, in enantiomerically pure form is presented.