Synthetic Applications Based on Dehydrogenative Alcohol Activation Catalyzed by Mn-, Fe and Co-Complexes

Background and Objectives: An environmentally benign method for the activation of an alcohol is based on its temporary conversion to a more reactive carbonyl compound by transition metal-catalyzed dehydrogenation. The use of homogeneous complexes in which noble metals were recently replaced by cheap, less toxic, earth-abundant metals (Mn, Fe, Co) enabled sustainable dehydrogenative coupling reactions of alcohols and X-nucleophiles (X: C, N, O). Greener synthesis of valuable chemicals (imines, amides, esters) occurred under acceptorless conditions, while direct alkylation of amines, alcohols and carbonyl compounds was achieved through borrowing hydrogen processes. Successful applications in the preparation of pharmaceutically interesting molecules (i.e. Piribedil) are discussed. The synthetic utility was further explored in the heterocycle synthesis. Aromatic (quinolines, pyrimidines, pyrroles) and non-aromatic heterocycles (lactones, lactams, cyclic amines and imides) were built up through single or multiple C-X bond formation.