Inverted Regioselectivities in the Reactions of Chlorine Atoms with Heteroarylmethanes

Authors

Rajive K. Khanna, University of Southern Mississippi
Becky Armstrong, University of Southern MississippiFollow
Hong Cui, University of Southern Mississippi
James M. Tanko, Virginia Polytechnic Institute and State University

Document Type

Article

Publication Date

7-15-1992

Department

Chemistry and Biochemistry

School

Mathematics and Natural Sciences

Abstract

The relative reactivities of the two methyl groups of 2,6-dimethylquinoline (2,6-DMQ) and 2,7 dimethylquinoline (2,7-DMQ) toward several radicals were assessed by intramolecular competitions. The regioselectivities observed for t-BuO^· and Br^· (k₆/k₂, k₇/k₂ > 1) are consistent with electrophilic characteristics of these radicals and estimates of relative stability of the resulting radicals. In contrast, Cl^· displays inverted selectivities (k₆/k₂, k₇/k₂ < 1) suggesting a directive effect of the DMQ nitrogen. Complexation of Cl^· by the N lone pair of dimethylquinolines, followed by a novel intramolecular hydrogen abstraction through a 5-center cyclic transition state, explains the regioselectivities observed in these reactions. Although bromine atoms also complex with heteroaromatics, the Br^· complexes have a low reactivity toward benzylic hydrogens. Evidence from intermolecular competition experiments, lasr flash photolysis studies, semiempirical MO calculations, and dimethylbutane quenching experiments is presented in support of the proposed intramolecular hydrogen abstraction process.

Publication Title

Journal of the American Chemical Society

Volume

114

Issue

15

First Page

6003

Last Page

6006

Recommended Citation

Khanna, R. K., Armstrong, B., Cui, H., Tanko, J. M. (1992). Inverted Regioselectivities in the Reactions of Chlorine Atoms with Heteroarylmethanes. Journal of the American Chemical Society, 114(15), 6003-6006.
Available at: https://aquila.usm.edu/fac_pubs/6818