Synthesis of polyhydroxylated pyrrolidines from sugar-derived bromonitriles through a cascade addition of allylmagnesium bromide/cyclization/reduction

Abstract

The synthesis of polyhydroxylated 2-allylpyrrolidines from sugar-derived bromonitriles in a cascade addition of allylmagnesium bromide/S_N2 cyclization/reduction with Zn(BH₄)₂ is described. The stereochemical course of the reduction step is rationalized. Two of the obtained compounds are transformed into stereoisomers of naturally-occurring iminosugar (+)-lentiginosine. In an alternative approach, 2,2-diallylpyrrolidines are obtained from bromonitriles in a cascade addition of allylmagnesium bromide/S_N2 cyclization/addition of another equivalent of allylmagnesium bromide.