Construction of adjacent spiro-quaternary and tertiary stereocenters through phosphine-catalyzed asymmetric [3+2] annulation of allenoates with alkylidene azlactones

A novel axially chiral spiro-phosphine-catalyzed highly regio-, diastereo- and enantioselective [3 + 2] cycloaddition of alkylidene azlactones with various allenic esters has been developed, affording the corresponding functionalized spirocyclic products in moderate to excellent yields under mild conditions. These spirocyclic products as masked amino acids can be easily transformed into aspartic amino acid analogues.