STEREOSELECTIVE REDUCTION OF GAMMA-OXOBUTANOIC ACIDS USING DIBAL-H AND ZNCL2

A variety of gamma-aromatic gamma-ketobutanoic acids can be reduced selectively, under optimized conditions, by the use of DIBAL-H and ZnCl2 to provide the (RS,SR)-gamma-aryl-gamma-hydroxy-beta-methylbutanoic acids. Further evidence has been gathered to support the hypothesis that the reaction proceeds by formation of a seven-membered ring complex with the aluminium or zinc atom bridging the ketone and carboxyl groups which preceeds the reduction step and that this templated reduction accounts for observed high diastereoselectivity. Also we have shown that some gamma-aryl-gamma-butyrolactones can be easily transformed via an oxidative cleavage of the aromatic ring to provide selective synthesis of either cis- or trans-tetrahydro-3-methyl-5-oxo-2-furancarboxylic acid derivatives.