CYCLOREVERSAL REACTION AND ORTHO INTERACTIONS IN 2-ARYL-4H-3,1-BENZOXAZIN-4-ONES ON ELECTRON-IMPACT

A cycloreversal reaction, leading to aroyl cations, is the major proce ss in 2-aryl-4H-3,1-benzoxazia-4-ones under electron impact conditions . The ortho interaction of the methoxy and the nitro groups in the 2-p henyl mtaieties in these compounds present the most abundant ions at m /z 119 and 134, respectively, in their mass spectra as a result of the transfer of a hydrogen atom from the former and an oxygen atom from t he latter to the imine nitrogen of the heterocycle. The ion structures and the mechanisms for the proposed fragmentations are based on high- resolution data, B/E and B-2/E linked-scan spectra, collision-activate d decomposition-B/E linked-scan spectra and deuterium labelling.