Iridium-Catalyzed\nOxidant-Free Transfer Dehydrogenation\nof Carboxylic Acids

Direct\ndehydrogenation of carboxylic acids to their unsaturated\ncounterparts represents a valuable transformation for complex molecule\nsynthesis, which, however, has been challenging to achieve. In addition,\nthe current carbonyl desaturation methods are almost all based on\noxidative conditions. Here we report an Ir-catalyzed redox-neutral\ntransfer dehydrogenation approach to directly convert carboxylic acids\nto either α,β- or β,γ-unsaturated counterparts.\nThese reactions avoid using oxidants or strong bases, thus, tolerating\nvarious functional groups. The combined experimental and computational\nmechanistic studies suggest that this transfer hydrogenation reaction\ninvolves directed C–H oxidative addition, β-H elimination,\nand dihydride transfer to an alkene acceptor with C(sp<sup>3</sup>)–H reductive elimination as the turnover-limiting step.