Interconversion of Nitrenes, Azirenes, and Diradicals: Rearrangement of 3-Isoquinolylnitrene to o-Cyanophenylketenimine and 1-Cyanoisoindole

• Published in: Journal of organic chemistry 2009-02, Vol.74 (3), p.1171-1178
• Main Authors: Vosswinkel, Michael, Lüerssen, Holger, Kvaskoff, David, Wentrup, Curt
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with only one n hetero atom and condensed derivatives; Heterocyclic compounds with several n hetero atoms in the same ring, in separated rings or in fused rings; Organic chemistry; Preparations and properties
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo802273y

Photolysis of tetrazolo[1,5-b]isoquinoline/3-azidoisoquinoline 22T/22A generates 3-isoquinolylnitrene 23, which has been characterized together with a diradical species (25) by Ar matrix ESR spectroscopy. Photolysis at λ > 300 nm generates azirene 24, characterized by IR spectroscopy, whereas further broad-band UV photolysis destroys the azirene to produce o-cyanophenylketenimine 17. The use of 15N-labeled tetrazole/azide 22T′/22A′ demonstrates rapid equilibration of two regioisomeric 15N-labeled azirenes 24′ and 24′′ prior to formation of 17. Flash vacuum thermolysis (FVT) of 22T/22A affords 1-cyano-2H-isoindole 27 in quantitative yield. FVT of 15N-labeled tetrazole/azide 22T′/22A′ causes scrambling of 15N label in the 1-cyano-2H-isoindole product. It is concluded that the interconversion of azirenes 24 takes place via the unobserved diazacycloheptatetraene/diazacycloheptatrienylidene 32/33, and that the rearrangement of azirene to ketenimine 17 and 1-cyanoisoindole 27 takes place via reversion to nitrene 23 followed by ring opening to diradical 25.