Enantioselective Borrowing Hydrogen: A Modern Tool to Construct Enantioenriched Molecules

In the quest for the more rapid and eco-compatible preparation of complex molecules from widely available ones, borrowing hydrogen is one of the most elegant manners to directly functionalize alcohols. Such catalytic cycles reduce the synthetic cost, and avoid waste and additional steps associated with adjusting the redox state for the functionalization of carbon chains. In this field, the last ten years have seen the development of general strategies to control the absolute stereochemistry of the created molecules. This enantiocontrol can arise from the three distinct steps of the catalytic cycle, namely the initial dehydrogenation, carbonyl functionalization or final hydrogen back-transfer. This review presents the different enantioselective approaches developed according to these principles and highlights the great potential of these transformations, the current limitations and future challenges. Borrowing hydrogen is a crucial approach in order to directly functionalize alcohols through reversible hydrogen transfer reactions. Through the appropriate implementation of chiral catalysts, the last decade has seen the development of enantioselective versions of these eco-compatible transformations. This review presents the principles behind these strategies that can provide a direct access to synthetically important enantioenriched scaffolds. image