Issue 12, 2002

N-Nitrosamide-mediated Ritter-type reactions.

Part II. The operation of “persistent steric” and “π*-acceptor agostic-type” effects

Abstract

Benzyl cations were generated via thermolysis of N-benzyl-N-nitrosopivalamide in molten 2-R-substituted benzonitriles (R = MeO, Me, H, F, Cl, and Br). The corresponding N-2-R-benzonitrilium species, in contrast to their 4-R-benzonitrilium counterparts, underwent limited reaction with pivalate ion to form unsymmetrical diacylamines via rearrangement of their initial imidic anhydrides. The yield of diacylamines, though small, varied systematically with the nature of the R group in a manner suggesting the operation of interesting steric and/or electronic effects on the pivalate ion-nitrilium ion collapse. The ortho-substituent, though present on only one side of the benzonitrilium ion inhibits reaction at both sides via steric hindrance in the near-ground state and steric crowding in the transition state (a “persistent steric” effect). The proposed electronic effect involves a π*-acceptor agostic-type interaction between n or σ electrons (HOMO) and the π* system (LUMO) of the nitrilium ion. Additionally, in many cases, attack by water on the nitrilium ion occurred to a significantly larger extent than attack by the much more nucleophilic and positionally favored pivalate ion on the same species. This observation is interpreted in terms of the differences in the sizes and docking trajectories of both species with the nitrilium ion due to charge and charge distribution on both nucleophiles.

Graphical abstract: N-Nitrosamide-mediated Ritter-type reactions. Part II. The operation of “persistent steric” and “π*-acceptor agostic-type” effects

Article information

Article type
Paper
Submitted
02 May 2002
Accepted
17 Sep 2002
First published
24 Oct 2002

J. Chem. Soc., Perkin Trans. 2, 2002, 2146-2153

N-Nitrosamide-mediated Ritter-type reactions.

R. W. Darbeau, R. S. Pease, E. V. Perez, R. E. Gibble, F. A. Ayo and A. W. Sweeney, J. Chem. Soc., Perkin Trans. 2, 2002, 2146 DOI: 10.1039/B204255J

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