title: Origin of regioselectivity in the reactions of nitronate and enolate ambident anions.
abstract: The reactions of nitronates of ring-substituted phenylnitromethanes and enolates of ring-substituted 1-phenyl-2-propanones with MeOBs gave exclusively the O-methylated and C-methylated products, respectively. DFT calculations suggested that two factors, namely, intrinsic barriers and metal-cation coordination, control the C/O selectivity. The kinetic preference for O-methylation in the reactions of nitronates arises from the intrinsic barriers, which are ca. 10 kcal/mol lower for O-methylation than for C-methylation. The situation is the same for the gas-phase reaction of an enolate, in which the O-methylation is more favorable than the C-methylation. The experimentally observed C-selectivity of enolate reactions in solution is due to the metal-cation coordination, which hinders O-methylation for enolates. The effects of the enolate reactivity and the solvent on the C/O selectivity are also rationalized to arise from the two factors.
authors.affiliation: Department of Chemistry and the Research Center for Smart Molecules, Rikkyo University, Nishi-Ikebukuro, Toshima-ku 171-8501, Tokyo, Japan.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Sakata
authors.forename: Natsuko
authors.initials: N
authors.lastname: Seki
authors.forename: Kozue
authors.initials: K
authors.lastname: Yomogida
authors.forename: Hiroko
authors.initials: H
authors.lastname: Yamagishi
authors.forename: Akino
authors.initials: A
authors.lastname: Otsuki
authors.forename: Chie
authors.initials: C
authors.lastname: Inoh
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamataka