Theoretical Study on the Ring-Opening Reactions of Cyclopropenes Mediated by a Au1 Complex

DFT calculations have been carried out in order to rationalize and predict the ring opening regioselectivity of substituted cyclopropenes in the presence of gold(I) catalysts. It has been shown that the regioselectivity of these ring opening processes is driven by the relative pi-donor ability of the substituents on the cyclopropene double bond (C1 and C2). A stronger pi-donor substituent at C2 favors Au(I)-induced polarization of the double bond toward Cl, resulting in preferential breaking of the C1-C3 bond. An excellent correlation between Delta E-double dagger and the difference in the C1-C2 p(pi) orbital population was observed for a broad range of substituents, providing a useful predictive model for gold-induced cyclopropene ring-opening. Furthermore, it was found that the stability of the resulting gold-stabilized allyl-cation intermediates do not follow the same trend as the ring opening reaction energies. Generally, the more facile ring opening process led to the less thermodynamically stable intermediate, which lacked stabilization of the carbocation by a pi-donor in the alpha-position.