To demonstrate the generality of this electrocatalytic protocol, C-C bond forming rearrangement and cyclization reactions were carried out (Figure ). For example, semi-pinacol rearrangement of a cyclobutane-containing allylic alcohol 9 was achieved, furnishing the ring-expansion product 10 in good yield. An intramolecular hydroarylation reaction was demonstrated (12). Cyclization at the -position of an amide likely proceeded via a radical rather than a cationic intermediate, which is in line with Vanderwal's proposal on HAT-initiated oxidative polyene cyclization. Compared to chemical oxidant-based systems, the electrocatalytic method displayed similar efficiency at lower expense and less organic waste production, which could be important for scaling up applications. A series of experiments were performed in order to probe the mechanism of the electrocatalytic hydrofunctionalization reactions (Figure ). First, cyclic voltammetry of Co complex 3a displayed a reversible oxidation event at E1/2 = -0.17 V vs. Fc + /Fc in methanol, which was not affected by the addition of silane (Figure ). Interestingly, the reduction wave disappeared upon adding potassium methoxide. It indicates that methoxide, which could be cathodically generated, might serve as a necessary catalyst for silane activation and thus effect the formation of Co-H from Co III . This also corroborates with the solvent effect observed during optimization (Figure , entry 5). Next, hydride transfer from the silane was confirmed by a deuterium-labeling experiment, whereas running the reaction in CD3OD provided nearly no D incorporation (Figure ). Interestingly, the D% incorporation was substantially lower than expected in the first case, which is most likely due to H/D scrambling by reversible HAT (rather than Co-D/H + exchange or oxidation of methanol). Further, the HAT process was evaluated by a radical clock substrate, where the ring-opening trapping product was predominantly observed, suggesting the radical nature of the intermediate generated by HAT (Figure ).