Enantioselective Synthesis of Polysubstituted Spiro-nitroprolinates Mediated by a (R,R)-Me-DuPhos AgF-Catalyzed 1,3-Dipolar Cycloaddition

The synthesis of constrained spirocycles is achieved effectively by means of 1,3-dipolar cyclodditions employing alpha-imino gamma-lactones as azomethine ylide precursors and nitroalkenes as dipolarophiles. The complex formed by (R,R)-Me-DuPhos 18 and AgF is the most efficient bifunctional catalyst. Final spiro-nitroprolinates cycloadducts are obtained in good to moderate yields and both high diastereo- and enantioselectivities. Density functional theory (DFT) calculations supported the expected absolute configuration as well as other stereochemical parameters.