Mechanisms of the reaction between polyhalogenated nitrobutadienes and electron-deficient anilines: computational modeling.

Nitro-substituted polyhalogenated butadienes are valuable synthetic precursors for polyfunctionalized bioactive heterocyclic compounds. Recently, a new reaction between 2-nitroperchloro-1,3-butadiene and electron-deficient anilines producing the Z stereoisomers of a variety of allylidene arylhydrazines has been reported. Although the formation of a chlorinated nitrile oxide intermediate was proved by trapping it with appropriate alkenes via 1,3-dipolar cycloaddition, the details of the overall mechanism remained unclear. The elucidation of the mechanism is important for a better understanding of polyhalogenated nitrobutadiene chemistry. We proposed six reaction paths for the formation of allylidene arylhydrazine, starting from 2-nitroperchloro-1,3-butadiene and para-nitro aniline, and generated the potential energy profiles with the DFT/B3LYP/6-31+G(d,p) method. To include the solvent effect, single-point energy calculations were carried out at the B3LYP/6-31+G(d,p) level by the polarizable continuum mode...