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

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 phosphine-catalyzed [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 γ- to the β′-carbon atom of the allenoate was observed during the annulations performed using sterically demanding chiral phosphines