Strategies for Carbon Electrophile Addition to Carbonyls and Imines by Cobalt Catalysis

The addition of carbon electrophiles to carbonyls and imines has emerged as a valuable strategy for the construction of C-C bonds. The merger of this concept with sustainable cobalt catalysis has yielded numerous innovative methodologies. Remarkable functional group tolerance and selectivity have been observed in many cases, providing reliable methods for bond construction. The cobalt-catalyzed additions of carbon electrophiles to carbonyls, imines and carboxylic acid derivatives described in this review include the earliest reports, such as Takai-Utimoto Co/Cr co-catalyzed additions and their progression, as well as modern variants, exemplified by recent Co/photoredox co-catalyzed protocols. The systematic appraisal of this modern strategy provides a clearer perspective and inspiration for its further development. Cobalt-catalyzed additions of carbon electrophiles to carbonyls, imines and carboxylic acid derivatives are reviewed. The review is organized based on the nature of the reductant used for generation of the active low-valent Co-species: chemical and photochemical reduction strategies. The mechanistic aspects of the strategies are also summarized.image