Eosin Y, a well-known economical alternative to metal catalysts in visible-light-driven single-electron transfer-based organic transformations, can behave as an effective direct hydrogen-atom transfer catalyst for C-H activation. Using the alkylation of C-H bonds with electron-deficient alkenes as a model study revealed an extremely broad substrate scope, enabling easy access to a variety of important synthons. This eosin Y-based photocatalytic hydrogen-atom transfer strategy is promising for diverse functionalization of a wide range of native C-H bonds in a green and sustainable manner.

A direct hydroalkylation of disubstituted alkynes with unfunctionalized ethers and amides was achieved in an atom-efficient and additive-free manner through the synergistic combination of photoredox and nickel catalysis. The protocol was effective with a wide range of internal alkynes, providing products in a highly selective fashion. Notably, the observed regioselectivity is complementary to conventional radical addition processes. Mechanistic investigations suggest that the photoexcited iridium catalyst facilitated the nickel activation via single-electron transfer.

Chlorine radical, which is classically generated by the homolysis of Cl under UV irradiation, can abstract a hydrogen atom from an unactivated C(sp )-H bond. We herein demonstrate the use of HCl as an effective hydrogen-atom-transfer catalyst precursor activated by an organic acridinium photoredox catalyst under visible-light irradiation for C-H alkylation and allylation. The key to success relied on the utilization of microtubing reactors to maintain the volatile HCl catalyst. This photomediated chlorine-based C-H activation protocol is effective for a variety of unactivated C(sp )-H bond patterns, even with primary C(sp )-H bonds, as in ethane. The merit of this strategy is illustrated by rapid access to several pharmaceutical drugs from abundant unfunctionalized alkane feedstocks.

A visible-light-induced highly selective alkylation and amination of unactivated C(sp 3 )-H bonds via the synergistic effects of an organo-photoredox catalyst and a bromine-based hydrogen atom transfer agent has been developed by applying CH 2 Br 2 as both the solvent and the bromine radical source. Our study offers a new paradigm for the direct synthesis of valuable compounds from abundant alkane feedstocks in a convenient and metal-free manner.