Nitrile Imine Cyclizations and Rearrangements: N -Phenyl- C -styrylnitrile Imine and N -Phenyl- C -phenylethynylnitrile Imine.

The formation and rearrangements of nitrile imines are of ongoing synthetic and theoretical interest. In this paper, we report a computational investigation at the M06/6-311 + G(d,p) level of the formation and rearrangement of propargylic N- phenyl -C- styrylnitrile imine 3 from 2-phenyl-5-styryltetrazole 1 by flash vacuum pyrolysis (FVP). Nitrile imine 3 cyclizes to 3a H -3-styrylindazole 4 , which is also generated by H-shifts in the FVP of 3-styrylindazole 8 . Tautomerization of 4 and N 2 -elimination afford cyclohexadienylidene 14 , which by cyclization followed by H-shifts yields the primary pyrolysis product, 3-phenylindene 5 . An alternate path via 7a H -3-styrylindazole, phenyl(styryl)diazomethane, and phenyl(styryl)carbene is potentially possible. The analogous pyrolysis of 2-phenyl-5-phenylethynyltetrazole 1' afforded cyclopenta[ fg ]fluorene and cyclopenta[ def ]phenanthrene via N -phenyl- C -phenylethynylnitrile imine 3' and 3a H -3-phenylethynylindazole 4' . In both cases, 3 and 3' , rearrangement to diazocyclohexadienes and cyclohexadienylidenes (e.g., 14 ) is energetically preferred over alternate aryldiazomethane and arylcarbene intermediates.