Enantioselective Synthesis of Spiropyrrolidines by Synergistic Catalysis
A stereoselective methodology for the synthesis of highly substituted spiropyrrolidines via synergistic catalysis was developed. The transformation is based on a cooperative catalytic system combining chiral phosphoric acid (CPA) catalysis with achiral palladium catalysis and proceeds through a formal [3+2] cycloaddition of activated vinylcyclopropanes with aldimines derived from imidazolones. Under the optimized reaction conditions, a broad range of spiropyrrolidines were obtained in good combined yields (up to 83%), with high diastereoselectivities (up to 1:12 dr) and enantioselectivities reaching 99% ee. The developed methodology tolerates various substitutions on both of the reaction partners. Furthermore, selected synthetic transformations demonstrated the utility of the obtained spiropyrrolidines for further derivatization while retaining the enantiomeric purity. This work highlights the potential of synergistic CPA/transition-metal catalysis for the efficient construction of structurally complex chiral spiropyrrolidine scaffolds.