Transient Stabilization Effect of CO 2 in the Electrochemical Hydrogenation of Azo Compounds and the Reductive Coupling of α-Ketoesters.

The carbon dioxide (CO 2 ) capture and utilization has attracted a great attention in organic synthesis. Herein, an unpresented transient stabilization effect (TSE) of CO 2 is disclosed and well applied to the electrochemical hydrogenation of azo compounds to hydrazine derivatives. Mechanistic experiments and computational studies imply that CO 2 can capture azo radical anion intermediates to protect the hydrogenation from potential degradation reactions, and is finally released through decarboxylation. The promotion effect of CO 2 was further demonstrated to work in the preliminary study of electrochemical reductive coupling of α-ketoesters to vicinal diol derivatives. For the electrochemical reductive reactions mentioned above, CO 2 is indispensable. The presented results shed light on a different usage of CO 2 and could inspire novel experimental design by using CO 2 as a transient protecting group.