title: Homologation of boronic esters with organolithium compounds: a computational assessment of mechanism.
abstract: Ab initio calculations are reported for the reaction of methyl boronic ester with organolithium reagents with α-leaving groups. The best calculations rely on density functional theory prediction of structures and coupled-cluster theory calculation of accurate potential energies. The results provide strong confirmation of the feasibility of a two-step mechanism with rapid initial formation of a boron-ate complex followed by slower migration of methyl from boron to carbon with loss of the leaving group. The calculated free energy of activation is consistent with observed kinetic behavior, and the calculations provide a framework for exploring substituent and other effects on reactivity. Obtaining reasonable agreement with experiment in this way is not trivial and requires careful treatment of level of theory (density functional theory calculations tend to yield inaccurate results), of conformational complexity, especially for the ate complexes, and of the nature of the microscopic model of reactants and solvent. The methodological challenges and possible pitfalls, many of which are relevant more broadly to computational modeling of organic reaction mechanisms, are discussed in detail.
authors.affiliation: School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Essafi
authors.forename: Simone
authors.initials: S
authors.lastname: Tomasi
authors.forename: Varinder K
authors.initials: VK
authors.lastname: Aggarwal
authors.forename: Jeremy N
authors.initials: JN
authors.lastname: Harvey
mesh_terms: D001897:Boronic Acids / Q000737:chemistry*; D003198:Computer Simulation; D004952:Esters; D018020:Lithium Compounds / Q000737:chemistry*; D008968:Molecular Conformation; D011789:Quantum Theory
chemical_list: D001897:Boronic Acids; D004952:Esters; D018020:Lithium Compounds