Organocatalyst in Direct C(sp2)-H Arylation of Unactivated Arenes: [1-(2-Hydroxyethyl)-piperazine]-catalyzed Inter- /Intra-molecular C-H bond activation

This article describes the identification of 1-(2-hydroxyethyl)-piperazine as a new, cost-effective, highly efficient organocatalyst which promotes both inter- as well as intra-molecular direct C(sp2)-H arylation of unactivated arenes in the presence of potassium tert-butoxide. While the inter-molecular C-H aryla-tion of unactivated benzenes with aryl halides (Ar-X; X = I, Br, Cl) towards biaryl syntheses underwent smoothly in the presence of only 10 mol% organocatalyst; the intra-molecular C-H arylation catalytic system comprises of 40 mol% each of the catalyst and the additive (DMAP). The novel catalyst is also able to perform both inter- as well as intra-molecular direct arylation simultaneously in a single pot. The mechanistic studies confirmed the involvement of aryl radical anion and proceeded via single electron transfer (SET) mechanism. The large substrate scope, high functional group tolerance, competition exper-iments, gram-scale synthesis and kinetic studies further highlights the importance and versatile nature of the methodology as well as the compatibility of the new catalyst. To the best of our knowledge, this is the first report by any organocatalyst reported in the literature which gives detailed extensive investiga-tions of both inter- as well as intra-molecular direct C(sp2)-H arylation of unactivated arenes in a single representation.