Rhodium-Catalyzed Regiodivergent and Enantioselective Hydroboration of Enamides

Chiral alpha- and beta-aminoboronic acids exhibit unique biological activities. General methods for the synthesis of these bioisosteres of amino acids are highly desirable. We report a facile preparation of these compounds through rhodium-catalyzed regiodivergent and enantioselective hydroboration of enamides. Catalytic asymmetric synthesis of alpha- and beta-aminoboronic esters with high regio-, diastereo-, and enantioselectivities were achieved through effective catalyst control and tuning substrate geometry. Starting from easily available materials, this strategy provides a unified synthetic access to both enantioenriched alpha-boration and beta-boration products. The synthetic utility of these methods was demonstrated by efficient synthesis of an anticancer drug molecule and diverse transformations of the boration products.