Interconversion of nitrenes, azirenes, and diradicals: rearrangement of 3-isoquinolylnitrene to o-cyanophenylketenimine and 1-cyanoisoindole.
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 lambda > 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.
Vosswinkel
Michael
M
School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia.
Lüerssen
Holger
H
Kvaskoff
David
D
Wentrup
Curt
C