Benzylic Lithium Compounds: The Missing Link in Carbon-Lithium Covalency. Dynamics of Ion Reorientation, Rotation around the Ring-Benzyl Bond, and Bimolecular C-Li Exchange

Overview of Carbanion Dynamics and Electrophilic Substitutions in Chiral Organolithium Compounds

“…43 The chelated α-silylbenzylic organolithium illustrated in Figure 10d enantiomerizes by a conducted tour mechanism, 44 that is, the lithium remains chelated by the tertiary amine as it moves from one face of the carbanion to the other. 45 Very similar dynamics were observed in an analogous allylic system in which the phenyl ring is replaced by a double bond. 46 Here again, the negative enthalpy of activation is consistent with additional solvation of the transition state.…”

“…Enantiomerization barriers for representative benzylic and allylic organolithiums (ΔG and ΔH (kcal/mol); ΔS (cal/mol·K)): (a) benzylic lithiohydrocarbon; 40 (b) α-thio benzylic organolithium; 43 (c) α-seleno benzylic organolithium; 42 (d) chelated α-silyl benzylic organolithium that enantiomerizes by a conducted tour; 45 (e) α-amino benzylic organolithium. 43 …”

The Mechanism of the Stereospecific Intramolecular Arylation of Lithiated Ureas: The Role of Li+ Probed by Electronic Structure Calculations, and by NMR and IR Spectroscopy

“…Characteristic signals shifted upfield from the aromatic region indicate that complete lithiation of the substrate 5b has given benzyllithium 5Li. [26] Delocalisation of charge into the ring accounts for the chemical shifts of the MeOC 6 H 4 aryl protons in the region of δ = 6-7 ppm and the partial double bond between the anionic centre and the ring results in doubling up of those signals. The signals between δ = 5.9 and 4.8 ppm marked with asterisks appear to arise from the in situ elimination of lithiated THF to yield lithium but-3-ene 1-oxide, which is not the usual THF decomposition pathway, [27] but one that has previously been observed in the presence of electron-rich ligands [hexamethylphosphoramide (HMPA) and DMPU].…”

Synthetic Applications and Inversion Dynamics of Configurationally Stable 2-Lithio-2-arylpyrrolidines and -piperidines

“…21 Cram and coworkers reported the enantiomerization of a chelated α-silylbenzylic organolithium 22 via the conducted tour mechanism. 23 In all of these examples, negative entropies of activation were observed, consistent with additional solvation in the transition state. In collaboration with the Coldham group, we have studied the dynamics of carbanion inversion of α-amino organolithium compounds.…”