Synthesis of tetronic acid derivatives from novel active esters of α‐hydroxyacids

Active esters, produced by condensation of O‐acetyl protected α‐hydroxyacids with N‐hydroxysuccin‐imide, react with anions of active methylene compounds to afford β,β‐tricarbonyl derivatives which upon deprotection undergo cyclization to 3‐alkoxycarbonyl and 3‐acyl tetronic acids. Incorporation of (S)‐2‐ace‐toxyphenylacetic acid in this reaction sequence enables the synthesis of optically active 5‐phenyltetronic acid derivatives.