We developed a ruthenium-catalyzed reductive ester synthesis from aldehydes or ketones and carboxylic acids using carbon monoxide as a deoxygenative agent. Multiple factors influencing the outcome of the reaction were investigated. Best results were obtained for commercially available and inexpensive benzene ruthenium chloride; as low as 0.5 mol % of the catalyst is sufficient for efficient reaction. Competitive studies demonstrated that the presence of even 1000 equiv of alcohol in the reaction mixture does not lead to the corresponding ester, which clearly indicates that the process is not a simple reductive esterification but a novel type of Ru-catalyzed redox process.
Rh-catalyzed one-step reductive amidation of aldehydes has been developed. The protocol does not require an external hydrogen source and employs carbon monoxide as a deoxygenative agent. The direction of the reaction can be altered simply by changing the solvent: reaction in THF leads to amides, whereas methanol favors formation of tertiary amines.