Direct and Enantioselective Vinylogous Michael Addition of alfa-Ethylidene Pyrazolinones to Nitroolefins Catalyzed by Dual Cinchona Alkaloid Thioureas

While several protocols exist for the asymmetric functionalization of pyrazolinones at the alfa-position relying on nucleophilic addition or annulation procedures, use of alfa-ethylidene electron-rich analogues in asymmetric vinylogous coupling to carbon electrophiles is substantially an uncharted domain. We now report, for the first time, that ethylidenepyrazolinones carrying an enolizable carbon at the gamma-position efficiently participate in direct and asymmetric, catalytic vinylogous Michael-type addition to nitroolefins providing the expected adducts in high yields, with complete gamma-site selectivity and with an extraordinary level of geometrical and enantioselectivity. Either R- or S- configured adducts were equally accessed by employing a quasi-enantiomeric quinine- or quinidine-based thiourea catalyst pair.