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

Abstract

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-18 O 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.

Studies in sulfur‐nitrogen nucleophilicity

“…We have to conclude that the evidence in support of an intramolecular rearrangement is inconclusive. To distinguish between intramolecular vs intermolecular rearrangement would require application of the endocyclic restriction test . This test has been used in related 5, 6, and 7‐endo cyclizations and shown to support an intermolecular process.…”

Electrophilic Amination: The Case of Nitrenoids

“…The results from Table 6 may need partial re‐evaluation, as later competition experiments by Beak et al. showed that the reaction is quite sensitive to the substitution on the nitrogen (Table 6, entries 10–12) 46. The bulkier the moiety, the less amination is observed, and it may require prolonged reaction times and/or raising the reaction temperature, which also leads to side reactions.…”

“…In both cases, the amination products were observed, whereas the distribution of deuterated products confirmed that the processes follow an S N 2 mechanism. Crossover experiments with 59 and 60 , both of which contain longer linkers were also attempted; however, no amination was observed 46…”

Phosphorus substituted hydroxylamine and hydroxamic acid derivatives: synthesis and reactivity

“…41 In order to distinguish between the intermolecular and intramolecular pathways, the conversion of 97 to 99 via carbanion 98 is studied. 13 The results obtained show that the reaction proceeds via a trigonal bipyramidal transition structure and that a large bond angle is required for nucleophilic displacement at nitrogen.…”