Asymmetric Michael Addition Induced by (<i>R</i>)-<i>tert</i>-Butanesulfinamide and Syntheses of Chiral Pyrazolidinone Derivatives

A highly diastereoselective Michael addition of (R)-N-tert-butanesulfinyl imidates 8 to α,β-unsaturated pyrazolidinone 3a has been developed to afford pyrazolidinones 10 possessing three contiguous stereocenters with good to excellent yield and excellent diastereoselectivity. A two-step conversion of reduction and cyclization provides the bicyclic pyrazolopiperidine 12 in a good yield. A series of pyrazolopiperidine derivatives 18 with a quaternary carbon center at C-3a are stereoselectively synthesized via alkylation or Michael addition.