Synthesis and stereochemistry of some bicyclic γ-lactones from parasitic wasps (Hymenoptera: Braconidae). Utility of hydrolytic kinetic resolution of epoxides and palladium(II)-catalyzed hydroxycyclization-carbonylation-lactonization of ene-diols

Abstract

A palladium(II)-catalyzed hydroxycyclization−carbonylation−lactonization sequence with appropriate pent-4-ene-1,3-diols provides efficient access to the bicyclic γ-lactones, 5-n-butyl- and 5-n-hexyltetrahydrofuro-[3,2-b]furan-2(3H)-ones (3) and (4), respectively, in both racemic and enantiomeric forms. Some of the substrate pent-4-ene-1,3-diols of high enantiomeric excess (ee) have been derived from racemic terminal epoxides by hydrolytic kinetic resolution (HKR) using cobalt (III)−salen complexes. (9Z,12R)-(+)-Ricinoleic acid also serves as a “chiral pool” source of other pent-4-ene-1,3-diols. These syntheses and enantioselective gas chromatography confirm the structures and absolute stereochemistry of the lactones in some species of parasitic wasps (Hymenoptera:  Braconidae). The highly abundant 5-n-hexyltetrahydrofuro-[3,2-b]furan-2(3H)-one (4) in Diachasmimorpha kraussii and D. longicaudata is of high ee (>99%) with (3aR,5R,6aR) stereochemistry.