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Nitrene–Nitrene Rearrangement under Thermal, Photochemical, and Electron‐Impact Conditions: The 2‐Azidopyridines/Tetrazolo[1,5‐ a ]pyridines
Author(s) -
Wentrup Curt,
Braybrook Carl,
Liu Shanshan,
Tzschucke C. Christoph,
Dargelos Alain,
Bégué Didier
Publication year - 2016
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201600655
Subject(s) - nitrene , chemistry , photochemistry , pyridine , mass spectrum , ring (chemistry) , fragmentation (computing) , flash vacuum pyrolysis , radical , nitrogen , electron ionization , mass spectrometry , computational chemistry , pyrolysis , medicinal chemistry , ion , organic chemistry , chromatography , ionization , computer science , operating system , catalysis
15 N‐Labeling demonstrates that the two nitrogen atoms in the 2‐pyridylnitrene radical cation 2 ·+ become equivalent prior to fragmentation in the mass spectrometer. Furthermore, the mass spectra of 6‐ and 7‐tetrazolo[1,4‐ a ]pyridine are identical, as are those of 5‐ and 8‐tetrazolo[1,5‐ a ]pyridine, thereby again demonstrating interconversion of the nitrogen atoms in 2‐pyridylnitrenes. These rearrangements parallel the reactions established under thermal (flash vacuum pyrolysis) and photochemical condition. Calculations of the energies of ground and transition states at the CASPT2(7,8) level support the notion that 2‐pyridylnitrenes undergo very easy and exothermic ring expansion to 1,3‐diazacycloheptatetraene 3 , both in the neutrals and the radical cations. In addition, the ring opening to 4‐cyanobutadienylnitrene 4 can take place in both the neutrals and the radical cations with modest activation barriers.