Transition structures for additions of lithium hydride and methyllithium to ethylene and acetylene

Advances in Carbolithiation

“…Theoretical calculations have shown that the reaction of MeLi with ethylene occurs through preliminary formation of a relatively stable π-complex followed by syn-addition across the carbon-carbon double bond that requires activation energies of 18-24 kcal mol −1 [4]. However, the high reactivity of organolithium reagents toward unsaturated substrates limits the wide application of carbolithiation reactions.…”

“…Indeed, when the reaction with alkynes takes place, the regio-and stereoselectivity of the process determine the isomeric ratio of the resulting substituted alkenes (Scheme 11.2, (1)). The stereochemistry of the reaction depends both on the mechanism (syn-vs anti-addition) [4] and the configurational stability of the resulting vinyl lithium species (Scheme 11.2, (2)). If carbolithiation is now performed on an alkene, two consecutive stereogenic centers can be created, and diastereo-and enantioselectivity must be controlled to obtain a single product (Scheme 11.2, (3)).…”

Chirally Modifiedn-Butyllithium: Tuning the Composition, Structure, and Enantioselectivity with Modular Fencholates

“…Similar repulsive interactions between endo methyl groups were identified as origin for the favored (R)-biaryl conformation in 2,2'-(bis-2-hydroxy-1,3,3-trimethylbicyclo-[2,2,1]hept-2-yl)-1,1'-biphenyl. an increased propensity for b-hydride eliminations) [27] and selectivities of the mixed anionic aggregate 3-Si, relative to 1. Furthermore, agostic interactions are formed between the lithium ions and the b-CH 2 units in 3-Si.…”

Alkali Metal Hydride Complexes: Well-Defined Molecular Species of Saline Hydrides

“…B 3þ , Al 3þ ). Previously, the multiple-bond addition reactions of monomeric LiH with ethyne and ethene respectively have been investigated by computational studies [74] and were predicted to proceed, though they show a significant activation barrier that is somewhat lowered by the presence of the Li þ cation as a Lewis acid. In a special case, in situgenerated LiH succeeded in reducing the CC bond of ynolates.…”