DMAP Catalyzed Domino Rauhut-Currier Cyclization Reaction between Alkylidene Pyrazolones and Nitro-olefins: Access to Tetrahydropyrano[2,3-c]pyrazoles.

Herein, we employ unsaturated pyrazolones in the Rauhut-Currier reaction for the first time. A domino Rauhut-Currier cyclization reaction has been developed between unsaturated pyrazolones and nitro-olefins. The trisubstituted tetrahydropyrano[2,3-c]pyrazoles were obtained in moderate to high yields with excellent diastereoselectivities. A few applications including a synthesis of disubstituted tetrahydropyrano[2,3-c]pyrazole have been demonstrated. A preliminary catalytic asymmetric version of this process was also studied with chiral DMAP catalysts.