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

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