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.

DOI: 10.1021/jo302103c

Cite this paper

@article{Sakata2012OriginOR, title={Origin of regioselectivity in the reactions of nitronate and enolate ambident anions.}, author={Tomomi Sakata and Natsuko Seki and Kozue Yomogida and Hiroko Yamagishi and Akino Otsuki and Chie Inoh and Hiroshi Yamataka}, journal={The Journal of organic chemistry}, year={2012}, volume={77 23}, pages={10738-44} }