Two unusual, competitive mechanisms for (2-ethynylphenyl)triazene cyclization: pseudocoarctate versus pericyclic reactivity.
The cyclization of (2-ethynylphenyl)triazenes in ODCB at 200 degrees C gives exclusively cinnolines, whereas addition of CuCl to 1,2-dichloroethane solutions of the triazenes at 50 degrees C results in the sole formation of isoindazoles. DFT calculations and deuterium labeling studies suggest the intermediacy of a 3-dehydrocinnolinium ion, produced through a pericyclic transition state. Calculations and trapping studies strongly implicate a carbene intermediate in isoindazole formation, which proceeds through a pseudocoarctate transition state.
Kimball
David B
DB
Department of Chemistry, University of Oregon, Eugene, Oregon 97403-1253, USA.
Herges
Rainer
R
Haley
Michael M
MM
D006571:Heterocyclic Compounds / Q000138:chemical synthesis*; D007191:Indazoles / Q000737:chemistry; D013816:Thermodynamics; D014226:Triazenes / Q000737:chemistry*
C453559:(2-ethynylphenyl)triazene; D006571:Heterocyclic Compounds; D007191:Indazoles; D014226:Triazenes