Organocatalytic Acceptorless Dehydrogenation of Alcohols

Abstract

Acceptorless dehydrogenation provides an oxidant-free route from alcohols to carbonyl compounds while releasing molecular hydrogen. However, broadly applicable transition-metal-free systems remain limited. Herein, an ion-pair organocatalyst system composed of a thiophosphoric acid hydrogen-atom-transfer catalyst and a tailored isoquinoline acceptor enables organocatalytic acceptorless dehydrogenation under 390 nm light irradiation at room temperature. The protocol is effective for a wide range of alcohols, including both benzylic and aliphatic substrates, and exhibits high functional-group compatibility. Site-selective dehydrogenation of diols is also feasible. Mechanistic experiments support a photoinduced ion-pair electron-transfer to generate a thiyl radical, α-C–H abstraction of the alcohol, subsequent single-electron oxidation to a carbocation intermediate, and deprotonation, accompanied by hydrogen evolution.