Synthesis of 2, 5-Diamino-p-benzoquinones via Aerobic Oxidative C(sp2)-C(sp2) Bond Cleavage and Mechanistic Studies

A facile synthesis of 2, 5-diamino-p-benzoquinones (DABQs) is reported under very mild conditions by mere crystallization. Mechanistic studies by density functional theoretical (DFT) calculations revealed an oxidative C(sp(2))-C(sp(2)) bond cleavage reaction mechanism via a dioxetane intermediate, from enamine oxidation of a mixture of ethyl vanillin and primary amines by triplet molecular oxygen. A second air oxidation event in the sequence of the reaction that results in C(sp(2))-C(sp(2)) bond formation is also described by DFT studies. The mechanistic insights enabled synthesis of both symmetric and unsymmetric DABQs from primary amines with a broad substrate scope.