Reductive Deoxygenative Functionalization of Alcohols by First-Row Transition Metal Catalysis

Alcohols are among the most accessible functionalities. Catalytic deoxygenative functionalization of alcohols is highly synthetically appealing. While significant progress has been made on the reactions with nucleophiles, the reactions with electrophilic coupling partners remain a real challenge. This manuscript highlights the advance in this direction, which is mainly achieved by the first-row transition metals. The low-valent titanium catalyst has shown the unique reactivity to homolytically cleave the C-OH bonds. The formed carbon radicals could either undergo reduction to give protonation products or couple with carbon fragments to form C-C bonds. This chemistry is initially realized using a stoichiometric amount of titanium reagents and later extended to catalytic variants. Nickel features a variety of oxidation states ranging from Ni-0 to Ni-IV, and both two-electron oxidative addition and single-electron process are involved in their activation of an electrophile. These properties enable nickel to catalyze reductive C-C coupling of alcohols with R-X electrophiles. The reaction is first reported on the reactions of allylic alcohols, then extended to benzylic alcohols and, very recently non-activated alcohols. Recent effort has resulted in many invaluable methodologies that highly improve the reaction efficiency for the construction of aliphatic C-C bonds. The use of cobalt and copper catalysts not only expands the substrate scope of these reactions but also shows the new reactivity and selectivity issues.