Visible Light Activation of Boronic Esters Enables Efficient Photoredox C(sp$^2$)-C(sp$^3$) Cross-Couplings in Flow

Abstract

We report herein a new method for the photoredox activation of boronic esters. Using these reagents, an efficient and high-throughput continuous flow process was developed to perform a dual iridium- and nickel-catalyzed C(sp$^2$)–C(sp$^3$) coupling by circumventing solubility issues associated with potassium trifluoroborate salts. Formation of an adduct with a pyridine-derived Lewis base was found to be essential for the photoredox activation of the boronic esters. Based on these results we were able to develop a further simplified visible light mediated C(sp$^2$)–C(sp$^3$) coupling method using boronic esters and cyano heteroarenes under flow conditions.