Transition Structure Geometries for Transfers of Neutral and Anionic Nitrogen to Lithiated Carbanions

The geometries of nucleophilic substitutions at neutral and anionic nitrogen by organolithium species have been investigated. The demonstration of an intramolecular conversion of 9 to 10 provides an endocyclic restriction test which supports a trigonal bipyramidal transition structure for nitrogen transfer. A lack of isotopic scrambling of 12a-¹⁸O during nitrogen transfer is taken to rule out reaction via an oriented ion pair. Attempted endocyclic restriction tests for transfers of formally anionic nitrogen with 32 and 33 were not successful. Reactions of n-butyl, s-butyl and tert-butyllithium reagents with 16, 23, 30, 31, and 36-38 generally afford higher yields with increasing substitution at the carbon of the organolithium reagent and with decreasing substitution adjacent to the nitrogen of the aminating reagent. These results are consistent with trigonal bipyramidal transition states for nucleophilic displacements of oxygen by carbon at neutral and anionic nitrogen.