Partial Hydrogenation of Aryl-Substituted Benzothiophenes, Benzofurans and Indoles by Photocatalytic Water Activation

High Resolution Image Download MS PowerPoint Slide Transition-metal-catalyzed hydrogenation of heteroarenes provides direct access to three-dimensional, semisaturated scaffolds but remains particularly challenging for sulfur-containing compounds due to catalyst poisoning and undesired desulfurization. As a result, general methods for the direct catalytic hydrogenation of aryl-substituted benzothiophenes to the corresponding 2,3-dihydrobenzothiophenes (DHBTs) are lacking. Herein, we report a photocatalytic phosphine-mediated radical hydrogenation using water as the hydrogen source, enabling direct access to DHBTs. The generality of this method was demonstrated by a broad substrate scope, including diverse aryl- and heteroaryl-substituted substrates as well as related benzofurans, indoles, and other N -heterocycles. Gram-scale and deuteration experiments further highlight the practicality of this approach.