The Theoretical Investigation Of Mechanism And Chemoselectivity Of Gold(Ⅰ)-catalyzed Nucleophiles To Yield Substituted Furans

The mechanisms of Gold(I)-Catalyzed Cycloaddition of1-(1-Alkynyl)cyclopropyl Ketones with Nucleophiles have been investigated based on densityfunctional theory, all calculations were carried out with the Gaussian03programs.Thegeometries, energies of all of the stationary points were fully optimized by using theB3LYP method with the6-31G(d, p) basis set for all atoms except for gold, which wasdescribed by the SDD. The relative energies were, thus, corrected for the vibrationalzero-point energies (ZPE, not scaled). The polarized continuum model (PCM) wasalso applied at B3LYP/PCM/6-311++G(d, p)(SDD for Au) to minish the effect of thesolvent on the reactions of interest. The dielectric constant was assumed as8.93forbulk dichloromethane solvent. Moreover, the natural bond orbital (NBO) theory wasapplied to analyze the NBO charge distributions of representative transition states atthe B3LYP/6-31G(d,p) level in the gas phase. The results of the calculations indicatethat the first step of the catalytic cycle is the cyclization of the carbonyl oxygen ontothe triple bond which formed a new and stable resonance structure of an oxonium ionand a carbocation intermediate. The subsequent step for expanded ring results in theformation of the final product and regeneration of the catalyst. Furthermore, theregioselectivity and effect of the substitution has been discussed including theanalysis of energy, bond length, NBO charge distributions in the rate-determining step.Our computational results are consistent with the experimental observations of Zhanget al.The whole paper consists of three chapters. Chapter1is mainly about thedevelopment and application of quantum chemistry and the characteristics ofGold(I)-Catalyzed Cycloaddition of1-(1-Alkynyl) Cyclopropyl Ketones withNucleophiles to Yield Substituted FuransIn chapter2, The theory of quantum chemistry and calculation methods of thispaper that offer us with userful and reliable quantum methods. The systems have beeninvestigated using Density Functional Theory (DFT), Transition States Theory. Thestructures of the reagents, products and transition states along the reaction paths havebeen obtained together with the potential energy surface and thermodynamic datum. The reaction mechanism has been discussed using these data which provide effectiveinformations for experiments.In chapter3, The mechanisms of Gold(I)-Catalyzed Cycloaddition of1-(1-Alkynyl) cyclopropyl Ketones with Nucleophiles have been investigated basedon density functional theory.The results of the calculations indicate that the first stepof the catalytic cycle is the cyclization of the carbonyl oxygen onto the triple bondwhich formed a new and stable resonance structure of an oxonium ion and acarbocation intermediate. The subsequent step for expanded ring results in theformation of the final product and regeneration of the catalyst. Our computationalresults are consistent with the experimental observations of Zhang et al.