A Radical Approach to Chiral β-Hydroxyboronate Esters via Synergistic Co/Cr Catalysis

Chiral β-hydroxyboronate esters are versatile intermediates in organic synthesis, serving as bioisosteres of β-hydroxycarboxylic acids and providing access to diverse functionalized molecules. Despite their broad applicability, efficient and general methods for their asymmetric synthesis remain underdeveloped. Here, we report a chromium-catalyzed radical-polar crossover strategy for the asymmetric addition of α-boronate alkyl chlorides to aldehydes, furnishing β-hydroxyboronate esters with a broad substrate scope and high enantioselectivity. The reaction proceeds via CoPc-mediated radical generation followed by Cr-catalyzed stereoselective addition. The resulting products undergo diverse transformations, including oxidation, cross-coupling, and amination, demonstrating their synthetic utility. Mechanistic studies support a monomeric Cr-catalyzed alkylation pathway, expanding the scope of asymmetric Cr catalysis and providing a complementary approach to ionic strategies for β-hydroxyboronate synthesis.