Chemodivergent, multicomponent domino reactions in aqueous media: l-proline-catalyzed assembly of densely functionalized 4H-pyrano[2,3-c]pyrazoles and bispyrazolyl propanoates from simple, acyclic starting materials

Abstract

A library of 4H-pyrano[2,3-c]pyrazol-6-amines was synthesized in excellent yield employing an L-proline-catalyzed, on-water four-component domino reaction from hydrazines, β-dicarbonyl compounds, nitriles and dialkyl acetylenedicarboxylates that generates two rings by the creation of C–C (two), C–N, CN and C–O bonds and presumably involves a sequence of hydrazone formation, cyclocondensation, Michael, [1,3]-hydrogen shift, Michael addition and 6-exo-dig annulation steps. When alkyl propiolates were employed, a three-component reaction took place furnishing alkyl 3,3-bis(5-hydroxy-1H-pyrazol-4-yl)propanoates via a double Michael domino process.