Enzymatic Kinetic Resolution and Chemoenzymatic Dynamic Kinetic Resolution of δ-Hydroxy Esters. An Efficient Route to Chiral δ-Lactones

A successful kinetic resolution of a racemic mixture of delta-hydroxy esters 1 was obtained via lipase-catalyzed transesterification (E value up to 360). The combination of the enzymatic kinetic resolution with a ruthenium-catalyzed alcohol racemization led to an efficient dynamic kinetic resolution (ee up to 99% and conversion up to 92%). The synthetic utility of this procedure was illustrated by the practical syntheses of delta-lactones (R)-6-methyl- and (R)-6-ethyl-tetrahydropyran-2-one and (S)-5-(tert-butyldimethylsiloxy)heptanal. The former are important building blocks in the synthesis of natural products and biologically active compounds, and the latter is a key intermediate in the synthesis of widely used commercial insecticide Spinosyn A.