Conical intersections and photoreactions of 2H-azirines

CASSCF calculations were performed on the n pi*- and pi pi*-excited states of 2H-azirine as well as some alkyl-substituted 2H-azirines. An S-1/S-0 conical intersection (CI) was located, through which a direct formation of nitrile ylide can occur. In addition, an S-2/S-1 CI was found, from which a barrierless reaction path leads to nitrene in the S-1-excited state. (C) 2000 Elsevier Science B.V. All rights reserved.