Cp*RhIII -Catalyzed Sterically Controlled C(sp3 )-H Selective Mono- and Diarylation of 8-Methylquinolines with Organoborons

Abstract

Herein, the Rh^III -catalyzed selective monoarylation and diarylation (symmetrical and unsymmetrical) of 8-methylquinolines with organoboron reagents are disclosed. The selective monoarylation of primary C(sp³ )-H bonds is achieved by using 7-substituted 8-methylquinolines or by changing the quantity of the aryl boronic acids. The method is also applicable for the arylation of 2-ethylpyridines, and the heteroarylation with thiophene-2-ylboronic acids. Symmetrical and unsymmetrical diarylation of 8-methylquinolines have been carried out in one-pot and sequential manner, respectively. Late-stage monoarylation of oxime derivatives and gram-scale synthesis of monoarylated products has also been carried out. A mechanistic study revealed that the current reaction is first order with respect to both reactants and a five-membered rhodacycle intermediate may be involved in the catalytic cycle.

Keywords: 8-methylquinolines; arylation; diarylation; organoborons; rhodium.