Co(II)-Catalyzed Isomerization of Enals using Hydrogen Atom Transfer

The catalytic isomerization of alkenes is a well-studied and valuable process in synthesis. Despite the development of numerous metal-catalyzed isomerization catalysts, methods for the selective isomerization of methylenic enal substrates have not been established. To develop a process for the synthesis of an enal acetate, the so called C5-Acetate that is important in the industrial preparation of vitamin A, we show here that Co(II)-based hydrogen atom transfer catalysts under H2 promote such isomerizations in high yield (often 90%) with low catalyst loading (0.1 mol%). D-labelling studies suggest both the enal isomerization process and catalyst activation by H2 to be reversible.