Co-Mabiq Flies Solo: Light-Driven Markovnikov-Selective C- and N-Alkylation of Indoles and Indazoles without a Cocatalyst.

Abstract

Indoles and indazoles are common moieties in pharmaceuticals and naturally occurring bioactive compounds. The development of light-driven methods using earth-abundant transition-metal catalysts offers an attractive route for functionalization of such compounds. Herein, we report a visible-light-induced method for the C3- and N-alkylation of indoles and indazoles with styrenes, catalyzed by Co complexes based on the macrocyclic Mabiq ligand (Mabiq = 2-4:6-8-bis(3,3,4,4-tetramethyldihydropyrrolo)-10-15-(2,2'-biquinazolino)-[15]-1,3,5,8,10,14-hexaene-1,3,7,9,11,14-N6). The photochemical behavior of two CoIII catalysts was examined: Co(Mabiq)Cl2 and the newly synthesized Co(MabiqBr)Cl2, which contains the Br-modified ligand. Both complexes undergo visible-light-induced homolysis that is significant to their activity but exhibit differences in reactivity. The alkylation reactions are regioselective, furnishing the alkylated indole and indazole products in a Markovnikov fashion with excellent yields of up to 96% across a broad range of substrates. Notably, in contrast to dual-transition-metal and photoredox-catalyzed cross-coupling reactions, our studies reveal that the Co complex plays a dual role─as a photosensitizer and catalytically active metal center with the Mabiq ligand offering regiocontrol.