Multicomponent synthesis of dihydropyrano[2,3-c]pyrazoles catalyzed by lipase from Aspergillus niger

Lipase from Aspergillus niger (ANL) was found to be an extremely effective catalyst for four-component synthesis of dihydropyrano[2,3-c]pyrazoles from a stoichiometric mixture of ethyl acetoacetate, hydrazine hydrate, aldehyde/ketone, and malononitrile in ethanol. The lipase ANL showed a broad range of enzymatic promiscuity toward various aromatic and aliphatic aldehydes as well as ketones. Use of environmentally benign biocatalyst, reusability of the catalyst, room temperature reaction conditions, no hazardous solvent, and excellent yields are some of the important features of this protocol.