Direct and Enantioselective Vinylogous Michael Addition of [alpha]-Alkylidenepyrazolinones to Nitroolefins Catalyzed by Dual Cinchona Alkaloid Thioureas

While several protocols exist for the asymmetric functionalization of pyrazolinones at the [alpha]-position relying on nucleophilic addition or annulation procedures, use of [alpha]-alkylidene electron-rich analogues in asymmetric vinylogous coupling to carbon electrophiles is substantially an uncharted domain. We now report, for the first time, that alkylidenepyrazolinones carrying an enolizable carbon at the [gamma]-position efficiently participate in direct and asymmetric, catalytic vinylogous Michael-type additions to nitroolefins providing the expected adducts in high yields, with complete [gamma]-site selectivity and with extraordinary levels of enantio-, diastereo-, and geometrical selectivities. Both enantiomeric adducts were equally accessed by employing a quasi-enantiomeric quinine- or quinidine-based thiourea catalyst pair.