Computational Insights Into The Selectivities Of Au（I）-Catalyzed Intramolecular Addition Of Hydroxylamine Group Onto Alkynes And The Fragmentation Of （CO）₅

Gold（I） complexes are the most effective catalysts for the electrophilic activation of alkynes under homogeneous conditions. And this is one of the most important stragety for the construction of C-C bond and C-X bond. In addition, the oxidation reactions of alkynes catalysed by gold（I） catalysts have attracted great attraction due to the atom and redox economy. Whether the α-oxo gold carbene intermediates exit in the reaction is still in debating. There are a lot of factors influencing the gold（I） catalysis, including the ligand effect, counterion effect, or even the silver effect. The author studied the intramolecular hydroxylamines addition to the alkynes catalyzed by gold（I） complex in detail and try to find out why the terminal alkyne favors the mode of 5-exo O attack, while for the phenyl substituted alkyne, 5-endo N attack takes place. In addition, the author considered the influence of the counterion NTf₂-. The formation of H-bond between the hydroxyl group and NTf₂- could increase the nucleophilic ability of the O center. Computational results suggest that three factors may account for the chemo- and regio-selectivities of the Au（I）-catalyzed intramolecular addition of hydroxylamine group onto alkynes,which are the nucleophilicity of the N/O center of the hydroxylamine group, the electrophilicity of the Au（I）-activated triple bond, and the ring strain of the formed intermediates respectively. In addition, the α-oxo gold carbenoid intermediate might not be a key intermediate in the subsequent reaction route to form 3-pyrrolidinone for the terminal alkyne substrate.The fragmentation of （CO）₅ to five molecules of CO is calculated to be highly exothermic and is allowed to be concerted by the Woodward-Hoffmann rules. Our calculations find that the D₅ h energy maximum is a multidimensional hilltop on the potential energy surface. This D₅ h hilltop is 16-₂0 kcal/mol higher in energy than a C₂ transition structure and 11-15 kcal/mol higher than a Cs transition structure. The reasons for the very high energy of the D₅ h hilltop are discussed, and the geometries of the two lower energy transition structures are rationalized on the basis of mixing of the e₂ HOMO and the a₂ LUMO of the hilltop.