4-Quinolylnitrene and 2-quinoxalinylcarbene

• Published in: Journal of physical organic chemistry 2011-10, Vol.24 (10), p.999-1008
• Main Authors: Addicott, Chris, Lüerssen, Holger, Kuzaj, Martin, Kvaskoff, David, Wentrup, Curt
• Format: Article
• Language: English
• Subjects: azides; carbenes; flash vacuum thermolysis; matrix isolation; nitrenes; photolysis
• ISSN: 0894-3230; 1099-1395
• DOI: 10.1002/poc.1904

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. 4‐Quinolylnitrene 21 and 2‐quinoxalinylcarbene 17 undergo ring expansion to the cyclic ketenimine 19 as well as ring opening to a nitrile ylide 25 and a ketenimine 26 in matrix photochemistry experiments. A second nitrene assigned as 24 is observed by ESR spectroscopy. Solution photolysis of 22 in the presence of dialkylamines leads to trapping of the azirene 23 to afford 5‐dialkylaminobenzo[e]‐1,4‐diazepines 35.