Density Functional Theory Study of the Metal-Catalyzed Cycloaddition of Indolyl-Allenes: Possible Reaction Pathways, Stereoselectivity, and Regioselectivity

The mechanism, stereoselectivity, and regioselectivity in the Au- and Pt-catalyzed cycloadditions of indolyl-allenes were explored by density functional theory (DFT). Three different catalytic systems, PtCl2, [JohnPhosAu]+, and [IPrAu]+, were selected as model catalysts. The DFT calculations revealed that the [JohnPhosAu]+ catalyst features a reaction pathway completely different from those of the PtCl2 and [IPrAu]+ catalytic systems. The PtCl2-catalyzed process preferably begins with cis coordination and leads to the R configuration products via cis [3+2] cycloaddition. Furthermore, the stereoselectivity of the indolyl-allenes is mainly controlled by the interaction energy. In the [JohnPhosAu]+-catalyzed process, a relatively lower distortion energy, observed for the new reaction pathway proposed by our DFT calculations, enables the formation of the S configuration products through the trans [3+2] cycloaddition step that becomes the principal pathway. On the other hand, the electronic properties of the substituent in the substrate have a combined influence on the selective formation of different products in the [IPrAu]+-catalyzed reactions. The obtained theoretical data explain well the formation of different products when using these three distinct catalytic systems and provide a theoretical foundation for selecting an optimal catalyst in such cycloaddition reactions of indolyl-allenes.