4‐Quinolylnitrene and 2‐quinoxalinylcarbene

Matrix photolysis of 4‐quinolyl azide 22 affords 4‐quinolylnitrene 21 , identified by electron spin resonance (ESR) and infrared (IR) spectroscopy. Minor absorptions assigned to azirene 23 (1741 cm −1 ) were also observed. Further photolysis affords strong absorptions at 1902 and 1909 cm −1 ascribed to the cyclic ketenimine 19 as well as weaker absorptions at 2044 cm −1 ascribed to the open‐chain ketenimine 26 and at 1982 cm −1 assigned to the open‐chain nitrile ylide 25 . Both 2‐(5‐tetrazolyl)quinoxaline 14 and triazolo[1,5‐ a ]quinoxaline 16 give rise to an absorption at 2084 cm −1 because of formation of the diazo compound 15 on mild flash vacuum thermolysis (FVT) with Ar matrix isolation of the product. Matrix photolysis of 16 affords diazo compound 15 , cyclic ketenimine 19 and open‐chain ketenimine 26 . 2‐Quinoxalinylcarbene 17 was also formed in the matrix photolysis and identified by its ESR spectrum. FVT of either 22 or 15/16 afforded 4‐quinolylnitrene, identified by its Ar‐matrix ESR spectrum. A second nitrene ESR signal obtained in several FVT and photolysis experiments from both 22 and 16 is ascribed to the phenylnitrene derivative 24 formed by ring opening of 2‐quinoxalinylcarbene 17 . FVT of 14 , 16 , and 22 affords 3‐cyanoindole 27 as the major product. Minor amounts of 2‐cyanoindole 28 , 4‐aminoquinoline 29 and 4,4′‐azoquinoline 30 are also formed. Preparative photolysis of 22 in solution in the presence of dialkylamines leads to trapping of the azirene 23 to afford 5‐dialkylaminobenzo[ e ]‐1,4‐diazepines 35 . Copyright © 2011 John Wiley & Sons, Ltd.