Mechanisms of the transition metal-mediated hydroarylation of alkynes and allenes

We report the theoretical analysis of the mechanism of the intramolecular cyclization of biaryl alkynes and allenes, catalyzed by electrophilic transition metal complexes and soft Lewis acids. These reactions proceed through initial pi-complexation of the alkyne or allene moiety, which triggers the nucleophilic attack of the arene via an endo- or exo-dig pathway in a Friedel-Crafts-type mechanism. In addition, alternative reaction mechanisms have been considered to account for some experimental observations. The computed results over a variety of substrates and catalyst systems agree with experimental evidence and suggest that both structural and electronic effects play a crucial role in the regioselectivity outcome and in the involvement of operative intermediates in the reaction pathway.