A hydrogen atom transfer-enabled photocatalytic system for direct heteroarylation of C(sp3)–H and C(sp2)–H bonds†

Abstract

Although photocatalytic reaction methodologies offer novel avenues for functionalizing C–H bonds under such conditions, the availability of universal and reliable hydrogen atom transfer reagents remains remarkably limited. In this study, we have designed a novel hydrogen atom transfer reagent precursor (HRP-1) with an appropriate reduction potential, capable of releasing a corresponding anion as an effective base. Furthermore, by developing a new photocatalyst Br-5CzBN based on 2,3,4,5,6-penta(9H-carbazol-9-yl)benzonitrile (5CzBN), we achieved the photocatalytic activation of HRP-1, thereby establishing a metal-free photocatalytic system for the direct heteroarylation of C(sp³)–H or C(sp²)–H bonds in alkanes, amines, ethers, alcohols, arylalkanes, or aldehydes. The reaction proceeds smoothly without the need for additional strong bases and oxidants, significantly enhancing the functional group compatibility of substrates. Notably, the direct functionalization of several complex molecules with considerable commercial value or biological activity has been successfully achieved, including late-stage functionalization of caffeine, theobromine derivatives, sclareolide, and salicylaldehyde.