Synthesis of Pyrrolo[3,4-c]pyrazole Derivatives by Intramolecular Cycloaddition of Nitrile Imines

Abstract

We have recently shown that furo[3,4-c]pyrazole and furo[3,4-c]isoxazole derivatives are available through a reaction sequence including the intramolecular cycloaddition of properly functionalized 1,3-dipoles¹. As a confirmation of the wide applicability of this synthetic principle, the preparation of pyrrolo[3,4-c]pyrazoles is here reported. Representatives of this ring system, often of interest in pharmacology, have been previously synthesized by the reaction of properly 4-substituted pyrroli din-3-ones with hydrazines^2–7 or by the cycloaddition of diazocompounds to maleimides^8–13.