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(sp2)‐C(sp2) 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(sp2)‐C(sp2) 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. Synthesis of symmetric and unsymmetric 2, 5‐diamino‐p‐benzoquinones from ethyl vanillin and primary amines is reported under very mild conditions. C(sp2)‐C(sp2) bond cleavage and C(sp2)‐C(sp2) bond formation by triplet molecular oxygen is described by DFT calculations.