We developed organocatalyst systems to promote the cleavage of stable C−H bonds, such as formyl, α-hydroxy, and benzylic C−H bonds, through a hydrogen atom transfer (HAT) process without the use of exogenous photosensitizers. An electronically tuned thiophosphoric acid, 7,7'-OMe-TPA, was assembled with substrate or co-catalyst N-heteroaromatics through hydrogen bonding and π−π interactions to form electron donor−acceptor (EDA) complexes. Photoirradiation of the EDA complex induced stepwise, sequential single-electron transfer (SET) processes to generate a HAT-active thiyl radical. The first SET was from the electron-rich naphthyl group of 7,7'-OMe-TPA to the protonated Nheteroaromatics and the second proton-coupled SET (PCET) from the thiophosphoric acid moiety of 7,7'-OMe-TPA to the resulting naphthyl radical cation. Spectroscopic studies and theoretical calculations characterized the stepwise SET process mediated by short-lived intermediates. This organocatalytic HAT system was applied to four different carbon−hydrogen (C−H) functionalization reactions, hydroxyalkylation and alkylation of N-heteroaromatics, acceptorless dehydrogenation of alcohols, and benzylation of imines, with high functional group tolerance.

In this study, we developed a linear‐selective allylation reaction of aldehydes using simple alkenes as starting materials by using a quadruple hybrid catalyst system. The reaction proceeded under mild conditions such as room temperature under visible light irradiation and was applicable to asymmetric reactions. The key for this reaction is the addition of Ni(BF4)2 ⋅ 6H2O catalyst to the previously reported ternary catalyst system, accelerating the allylic transfer process from branch products to thermodynamically stable linear products by increasing the Brønsted acidity of thiophosphoric imide (TPI) catalyst.