Mechanism of Phosphine-Catalyzed Allene Coupling Reactions: Advances in Theoretical Investigations

Organocatalysis has emerged as an effective strategy for chemical synthesis. Within this area, phosphine-catalyzed coupling reactions have attracted considerable attention because of their versatility and wide range of applications in the construction of new C-C bonds. Recently, various experimental studies on the phosphine-catalyzed coupling reaction of allenes have been reported, and mechanistic and computational studies have also progressed considerably. As a nucleophile, phosphine can react with an allene to form a zwitterionic phosphoniopropenide intermediate. After stepwise cycloaddition and proton transfer, the phosphine catalyst can be regenerated by C-P bond cleavage. Alternatively, the zwitterionic phosphoniopropenide intermediate could also be protonated by a BrOnsted acid to generate a phosphonium intermediate, which can be used to construct new C-C bonds by electrophilic addition. In this review, we have summarized details of mechanistic studies of phosphine-catalyzed allene coupling reactions that follow these two reaction modes. In addition to detailing the reaction pathway, the regioselectivity and diastereoselectivity of the phosphine-catalyzed allene coupling reaction are also discussed in this review.