Efficient asymmetric synthesis of the four diastereomers of diphenacoum and brodifacoum

A highly stereo- and enantio-selective approach to the four stereoisomers of the rodenticides, diphenacoum and brodifacoum, is described. The key step involves the stereospecific formation of one of the crucial bonds in the molecular backbone, and is based on asymmetric organocopper 1,4-addition to chiral imides. Intramolecular cyclization of the resulting butanoate and coupling with 4-hydroxycoumarin, afford the title compounds. (C) 1997 Elsevier Science Ltd.