A Highly Efficient Cross-Coupling Mode via the Release of Small Molecules: Transition Metal-Catalyzed Unimolecular Fragment Coupling (UFC)

As a recently developed redox-neutral coupling reaction, transition-metal-catalyzed unimolecular fragment coupling (UFC) has been extensively investigated over the past decade. In comparison to conventional cross-coupling reactions, cross-electrophilic coupling (XEC) and cross-dehydrogenative coupling (CDC) protocols eliminate the need for stoichiometric organometallic reagents, reductants, or oxidants. Additionally, it produces only minimal molecular by-products for the formation of a series of C-C bonds and C-X bonds with high atom efficiency. This review presents a summary and classification of the research progress made over the past decade in this field. The research is classified into four main categories, decarbonylation, decarboxylation, desulfonylation, and deisocyanation, according to the type of small molecule that is liberated from the reaction system. This facilitates the implementation of more practical, straightforward, and expedient reaction operations. It is noteworthy that the reaction employs carbonyl compounds (aldehydes, ketones, carboxylic acid derivatives, etc.), sulfones, and amides, which are typically inexpensive and accessible, as reaction substrates. This groundbreaking synthetic approach has since yielded a plethora of outcomes and novel research avenues in related fields, while also offering benefits to other related fields.