Synergistic One‐pot Tandem Combination of Cu and Proline Catalysis: Stereodivergent Synthesis of Chiral Aldols from Primary Alcohols

A new stereodivergent one-pot tandem protocol, which granted diastereo- and enantioselective access to chiral aldols by starting from simple primary alcohols, is presented as a proof-of-concept. The synergistic combination of a chemoselective Cu(II)-catalyzed oxidation of primary alcohols into the corresponding aldehydes (without the expected overoxidation into the corresponding carboxylic acids and using simple aerial O2 as co-oxidant), followed by a concomitant organocatalyzed enantioselective aldol coupling promoted by the system (S)-proline/HTBD-BF4 [TBD = 1,5,7-triazabicyclo[4.4.0]dec-5-ene], was achieved after fine-tuning and compatibilizing the conditions required for the successful performance of both catalytic systems. Here, we demonstrated that selection and pairing of both catalysts needs to be extremely judicious to avoid orthogonality, kinetic, concentration or reciprocal poisoning issues. Refinement of the overall tandem protocol allowed us to design a synergistic and stereodivergent protocol which affords comparable or even better diastereoselective results than the organocatalytic system by itself. Finally, the following key factors (from a sustainable point of view) should be highlighted: i) no external VOC solvents are needed during our one-pot tandem synthetic protocol (by working under neat conditions); and ii) isolation/purification of any intermediate is not required, thus reducing the chemical waste and energy/time costs, simplifying the practical aspects of our synthetic methodology