Total synthesis of indole and dihydroindole alkaloids. XI.1,2 The synthesis of leurosine and the coupling of 3α,4α-substituted catharanthine derivatives with vindoline

Abstract

A detailed study involving the Polonovski-type coupling of vindoline (2) with several novel catharanthine derivatives is described. Coupling of vindoline (2) with the N-oxide intermediate of 3β,4β-epoxydihydrocatharanthine (1) provides a laboratory synthesis of the bisindole alkaloid leurosine (3, R=CO2CH3) and an unambiguous proof of the stereochemistry of the epoxide function in that alkaloid. The coupling of 2 with the N-oxides of 3α,4α-epoxydihydrocatharanthine (4) and 4α-hydroxydihydrocatharanthinic acid lactone (6) provide the rearranged bisindole products 5, 7, and 8.