A three-step procedure for the conversion of γ-lactones into δ-lactones

Abstract

γ-Lactones with a wide range of functional groups are transformed by a three-step procedure into the corresponding δ-lactones in an overall yield of up to 55%. The novel methodology involves the reduction of a γ-lactone to a γ-lactol followed by a Horner olefination with an excess of lithiated diethyl α-cyano-α-xdimethylaminomethylphosphonate to yield a mixture of E/Z-isomeric α-cyano enamines. Acidic hydrolysis of these intermediates affords the desired δ-lactones. By the same reaction sequence δ-lactones can be transformed into the corresponding ε-hydroxy carboxylic acids.