Efficient Synthesis of α‐Oxygenated Esters via Cobaloxime Catalyzed Carbene Insertion into OH Bonds

The formation of CO bonds represents a significant area of research in synthetic chemistry, particularly for the preparation of α‐oxygenated esters, which serve as key structural motifs in many biologically active molecules. Despite considerable progress, the development of efficient and general methods for CO bond construction remains a pressing challenge. Transition metal‐catalyzed carbene insertion into OH bonds has emerged as a powerful strategy for CO bond formation; however, these transformations have predominantly relied on noble metal catalysts. While base metal catalysts have been explored to a limited extent, cobalt‐catalyzed carbene insertion into OH bonds remains rare. Herein, we report the cobalt‐catalyzed carbene insertion into OH bonds using diazo compounds as carbene precursors. A broad range of substrates, including alcohols, phenols, carboxylic acids, benzoic acids, and even water, are well‐tolerated under the optimized conditions, affording the corresponding α‐oxygenated esters in yields of up to 97%. Furthermore, the applicability of this methodology to O‐containing bioactive molecules highlights its potential for late‐stage functionalization.