Diversified Synthesis of Chiral Fluorinated Cyclobutane Derivatives Enabled by Regio‐ and Enantioselective Hydroboration

The diversified synthesis of chiral fluorinated cyclobutane derivatives has remained a tough task in synthetic chemistry. Herein, we present a switchable paradigm for asymmetric hydroboration and formal hydrodefluorination of gem‐difluorinated cyclobutenes via rhodium catalysis, providing chiral gem‐difluorinated α‐boryl cyclobutanes and monofluorinated cyclobutenes with excellent regio‐ and enantioselectivity, respevtively. The key to the success of the two transformations relies on an efficient, mild and highly selective rhodium‐catalyzed asymmetric hydroboration with HBPin (pinacolborane), in which the subsequent addition of a base, and a catalytic amount of palladium if necessary, results in the formation of formal hydrodefluorination products with the four‐membered ring retained. The obtained chiral gem‐difluorinated α‐boryl cyclobutanes are versatile building blocks, which provides a platform for the synthesis of enantioenriched fluorinated cyclobutane derivatives to a great diversity.