1,3-Dipolar cycloaddition of nitrile imines with functionalized acetylenes: Regiocontrolled Sc(OTf)3-catalyzed synthesis of 4- and 5-substituted pyrazoles

Abstract

1,3-Dipolar cycloaddition of C-aryl-N-aryl- and C-carboxymethyl-N-aryl- nitrile imines with functionalized acetylenes have been studied. Regioisomeric mixtures have been obtained with the 5-substituted pyrazole as the major cycloadduct. Under scandium triflate catalysis a reversal in the regiochemistry was observed, especially in the case of C-carboxymethyl-N-aryl-nitrile imines. © Georg Thieme Verlag Stuttgart.