An improved and scalable synthesis of zolpidem via a CuI/BINOL-mediated tandem reaction of imine and alkyne

Abstract

An improved and scalable method for the synthesis of zolpidem (1), a hypnotic drug, was developed. A two-step sequence involving imine formation and subsequent tandem reaction between an imine and propiolamide in the presence of CuI/BINOL, an efficient promoter for the tandem reaction, is described. Zolpidem was efficiently prepared in a 54% isolated yield and the hemitartrate salt of zolpidem was produced in 37% yield by simple crystallization, without tedious column chromatography. The procedure can be scaled up to >10 g. The yield of 1 increased to 83% following isolation of the intermediate imine 5.