Isochalcogenourea-catalysed enantioselective synthesis of pyrrolidinone and chromeno-pyrrolidine heterocycles

Pyrrolidinone-containing heterocycles are important scaffolds in natural products and highly relevant for the pharmaceutical industry. Although previous reaction processes have addressed the asymmetric synthesis of these heterocycles, the use of readily available, cheap and bench-stable precursors (such as α,β-unsaturated esters) is still of synthetic interest. Herein we present the isochalcogenourea-catalysed chemo- and enantioselective synthesis of pyrrolidinones (γ-lactams) in up to 95% yield, 95:5 dr and 94:6 er via a Michael addition/hydrolysis/lactamisation cascade. The corresponding Michael addition product could be isolated prior to hydrolysis and functionalised to generate a range of ester and amide products in up to 81% yield, > 95:5 dr and 98:2 er. In addition, a switch in chemoselectivity to obtain chromeno-pyrrolidines in up to 58% yield, > 95:5 dr and 99:1 er via a Michael addition/intramolecular Mannich reaction/lactonisation sequence was achieved. Strategic placement of an ortho-hydroxy group within the benzophenone imine moiety was used to increase imine electrophilicity via hydrogen bonding and therefore facilitate the intramolecular Mannich reaction.