Chiral aminophosphines derived from hydroxyproline and their application in allene–imine [4 + 2] annulation

Abstract

A robust synthetic route from L-hydroxyproline (L-Hyp) to phosphines has established an expandable library of six chiral aminophosphines, which were then applied to the phosphinecatalyzed [4 + 2] allene-imine annulation. The enantioinduction in the annulations-induced by a purely steric effect-were moderate (up to 57% ee). A switch of the reaction site from the γto the β′-carbon atom of the allenoate was observed during the annulations performed using sterically demanding chiral phosphines. chiral [2.2.1] bicyclic phosphines [17,18]. Recently, we applied one such bridged bicyclic P-chiral phosphine, exo-(p-anisyl)-Hyp-Phos, in the asymmetric allene-imine [4 + 2]