REDIRECTING FORMATE DELIVERY TOWARD ALKENES: REGIOSELECTIVITY SWITCH VIA COBALT/PHOTOREDOX/BRØNSTED ACID CATALYSIS

Herein, we present a new photochemical approach for branched-selective carboxylation of vinylarenes with formate salts. Whereas, the linear selective carboxylation via CO2•– generation and successive Giese-type addition was previously developed, the switch on regioselectivity has been realized by combining with MHAT strategy by cobalt/ Brønsted acid/ photocatalysis. Here, we have been successful in synergistically equilibrate the kinetics between formate activation and MHAT cycle so that the persistent radical effect could play its role by introducing a diprotonated DABCO as a novel bench- and air-stable precatalyst for both the cycles. A range of vinylarenes have been carboxylated in this branched-selective fashion to produce carboxylic acids bearing all-carbon quaternary centers.