Enantioselective access to tetrahydropyrano[2,3-c]pyrazoles via an organocatalytic domino Michael-hydroalkoxylation reaction

An asymmetric domino Michael-hydroalkoxylation reaction of trans-α-alkynyl-nitroolefins with N-arylpyrazolinones has been accomplished using a chiral bifunctional squaramide catalyst. Under the organocatalytic method, a broad range of tetrahydropyrano2,3-c]pyrazoles with an exocyclic alkene at the C-6 position were prepared in high yields and excellent stereoselectivities. The presence of an exocyclic double bond and nitro group in the pyranopyrazoles provide a wide scope for further structural transformations.