1-Bromo-1,2-dicyanoethylene: A dicyanoacetylene synthon useful in tetraazaporphyrin synthesis

Abstract

Dicyanoacetylene, a highly reactive dienophile, readily reacts to form substituted maleonitriles which serve as precursors to soluble tetraazaporphyrins. Unfortunately, dicyanoacetylene is difficult to synthesize in large quantities. We report here a new dicyanoacetylene synthon, 1-bromo-1,2-dicyanoethylene, which is easily made in high yield by reaction of elemental bromine with fumaronitrile and easily purified by vacuum distillation. The resulting 5:1 mixture of geometric isomers reacts with dienes via a Diels–Alder reaction followed by elimination of HBr to give substituted maleonitriles. We demonstrate the utility of these reactions by reporting the synthesis of a novel, soluble tetraazaporphyrin bearing four 1,4-fused cyclohexyl groups on the macrocycle periphery.