Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
The mechanism of the photochemical decomposition of 1,4-oxazin-2-one to azacyclobutadiene and carbon dioxide was investigated by the semi-empirical MO method SINDO1. The relevant singlet and low-lying triplet potential energy hypersurfaces were studied and intermediates and transition structures were optimized with limited configuration interaction. The first step transforms 1,4-oxazin-2-one into a bicyclic lactone via internal cyclization. Then a stepwise bond breaking mechanism on the first excited triplet state yields azacyclobutadiene and CO2, whereas a reaction on the first excited singlet state is not common. It is shown that a simultaneous bond-breaking mechanism on the first excited singlet or on the first excited triplet is possible.
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