Atom- and Step-Economical Ruthenium-Catalyzed Synthesis of Esters from Aldehydes or Ketones and Carboxylic Acids.

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.