Stereoselectivity in the Reactions of Nitrosopiperidine Carbanions. Steric vs. Stereoelectronic Control

Abstract

The anion of N-nitroso-4-phenylpiperidine reacts with methyl iodide, carbon dioxide, and benzophenone to give solely the axial substitution product. A second methylation of the monomethyl derivative gave the 2,6-diaxial derivative. None of the isomer having trans methyl groups could be detected. This trans isomer dominates over cis by 75:25 at equilibrium. From a consideration of the steric interactions present in these nitrosamines, it can be concluded that they alone cannot explain the observed high stereoselectivity. It is proposed that stereoelectronic control contributes significantly to the exclusive axial attack.