The Darbeau-White-Gibble reaction: an N-nitrosoamide-mediated Ritter-type reaction. Part I. A study of electronic, steric, and orbital effects in thenucleophile

Benzyl cations were generated via thermal decomposition of N-benzyl-N-nitro sopivalamide in molten 4-R-substituted benzonitriles (R=NH2, Me2N, MeO, Me, H, F, and CF3). In each case, the benzyl cation was intercepted competitiv ely by pivalate ion to yield benzyl pivalate and by the benzonitriles to yi eld the corresponding N-4-R-benzonitrilium ion. The latter onium ions react ed with pivalate ion to form benzimidic anhydrides which rearranged to yiel d N-4-R-benzoyl-N-pivaloylbenzylamines (i.e. unsymmetrical diacylamines). T he yield of diacylamines (maximum similar to 10.6% for R=H) is smaller than from the corresponding reactions in acetonitrile and varied systematically with the nature and location of the R group on the aromatic nucleus. Both electron-releasing and electron-withdrawing groups at the para position eff ected a diminution of the yield of diacylamine; indeed for R=NH2, no diacyl amine was formed. ortho Substitution of the aromatic nucleus resulted in si gnificantly diminished yields of diacylamine, as did nucleophilic attack on the nitrilium ion by pivalate rather than acetate. Thus, both electronic a nd steric effects in nucleophilic attack on the nitrilium carbon were obser ved. The ratios of counterion-derived product to solvent-derived product fo r both the first-formed benzyl cation and the less reactive benzonitrilium ion are similar. This observation is interpreted in terms of the intermedia cy of nitrogenous entity-separated ion-pairs in these deaminations.