We report a highly diastereo- and enantio-selective allylation of azlactones catalyzed by the combination of a metallacyclic iridium complex and an optically inactive phosphate anion. The process demonstrates an approach for conducting diastereoselective reactions with prochiral nucleophiles in the presence of metallacyclic allyliridium complexes. The reaction provides access to an array of enantioenriched allylated azlactones containing adjacent tertiary and quaternary carbon centers. Preliminary mechanistic studies suggest that the phosphate and methyl carbonate anions together induce the unusually high diastereoselectivity.