Nitrile Imine Cyclizations and Rearrangements: -Phenyl--styrylnitrile Imine and -Phenyl--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 phenylstyrylnitrile imine from 2-phenyl-5-styryltetrazole by flash vacuum pyrolysis (FVP). Nitrile imine cyclizes to 3a-3-styrylindazole , which is also generated by H-shifts in the FVP of 3-styrylindazole . Tautomerization of and N-elimination afford cyclohexadienylidene , which by cyclization followed by H-shifts yields the primary pyrolysis product, 3-phenylindene . An alternate path via 7a-3-styrylindazole, phenyl(styryl)diazomethane, and phenyl(styryl)carbene is potentially possible. The analogous pyrolysis of 2-phenyl-5-phenylethynyltetrazole afforded cyclopenta[]fluorene and cyclopenta[]phenanthrene via -phenyl--phenylethynylnitrile imine and 3a-3-phenylethynylindazole . In both cases, and , rearrangement to diazocyclohexadienes and cyclohexadienylidenes (e.g., ) is energetically preferred over alternate aryldiazomethane and arylcarbene intermediates.