Theoretical Studies On Mechanism Of TpW?NO??PMe₃?-catalyzed Pyrrole To Form Azanorbornane And Rh₂?OPiv?₄-catalyzed The Transformation Of Triazole To Imidazole/thiazole

In current,computation chemistry is a common and important tool in the chemical fields.The chemical research is promoted a new height through the combination of theory and experiment.In the study of the chemical reaction mechanism,the prediction or verification of selectivity,and the design of catalyst molecule,density functional theory(DFT)is very popular and important.Simultaneously,it can better balance the difference between experiment and theory.In this paper,DFT is uesd to study TpW(NO)(PMe3)-catalyzed cycloaddition of 2,5-dimethylpyrrole and cis-/trans-dimethyl fumarate and Rhodium(?)-catalyzed cyclization of 1,2,3-triazoles and isocyanates/isothiocyanates.The cyclization mechanism and specific selectivity are rationally represented and explained.At first,the mechanism and selectivity of the cycloaddition of 2,5-dimethylpyrrole and trans-/cis-dimethyl fumarate in the complex TpW(NO)(PMe3)are investigated.TpW(NO)(PMe3)(?2-3H-2,5-dimethyl pyrrole)separately undergoes the transfer of TpW(NO)(PMe3)from C2-C3 double bond into the nitrogen,the hydrogen transfer from C4 into C,atom,the hydrogen transfer from C,to W atom,and a reductive elimination to isomerize into TpW(NO)(PMe3)(?2-1H-2,5-dimethylpyrrole).For trans-dimethyl numarate,the concerted is the optimal pathway.For cis-dimethyl fumarate,it is the most possible to involve a concerted cycloaddition to give a cis-adduct,ring opening of cis-adduct to give a cis-zwitterionic intermediate,the C6-C7 bond rotation of cis-zwitterionic intermediate to give trans-zwitterionic intermediate,and the ring closing of trans-zwitterionic intermediate to give trans-7-azanorbornane.Our computational results are in agreement with the experimental observations.The mechanism of Rh(?)-catalyzed ring transformation of 1-mesyl-4-phenyl-1,2,3-triazoles with isocynate and isothiocyanate have been explored by using DFT/B3LYP calculations.The comparison of possible reaction pathways shows that isocynate prefers to stepwise cycloaddition,and isothiocyanate prefers to concerted process.The chemoselectivity follow the order:C=S>C=N>C=O,which is in agreement with the experimental results.