Asymmetric synthesis of pyrano[2,3-c]pyrazoles via a cascade reaction between Morita–Baylis–Hillman acetates of nitroalkenes and pyrazolones

Abstract

The first organocatalytic enantioselective cascade reaction of Morita–Baylis–Hillman acetates of nitroalkenes with pyrazolones has been developed. With 20 mol% of chiral tertiary-amine squaramide, 1,4,5,6-tetrahydropyrano[2,3-c]pyrazoles were afforded in moderate yields (up to 71%) with excellent stereoselectivities (up to>99:1 dr and up to 98% ee).