Theoretical Studies On Polar1,3-dipolar Cycloaddition And[1,2]-shift Reactions Between Azocarbenium Ions With Multiple Bonds

In this paper, we have investigated the polar1,3-dipolar cycloaddition and subsequent [1,2]-shift reactions between azocarbenium ions and carbodiimides, acetylenes using DFT. In addition, we summarized the cycloaddition and subsequent [1,2]-shift reactions between azocarbenium ions and five dipolarophiles in order to unravel the mechanistic mystery and regio-as well as stereochemistry of the cycloaddition products.The first chapter is a breif review. The polar1,3-dipolar cycloaddition and subsequent[1,2]-shift reactions between azocarbenium ions and dipolarophiles were summarized. So it is theorically and pratically significative for us to choose the title reactions as research object, discussing the mechanistic and regio-as well as stereochemistry of these reactions.The chapter2has briefly introduced the fundamental theory and method of quantum chemistry. And necessary explanation were added for the analytical methods in the paper, such as local version of HSAB principle, natural bond orbital theory and Laplacian, LOL, RDG function based on localized electron analysis.In chapter3, the polar1,3-dipolar cycloaddition and subsequent [1,2]-shift reactions between azocarbenium ions and carbodiimides were studied and we focused on the mechanism of the cycloaddition and regio-as well as stereochemistry of the products. It indicates that, for the cycloaddition between azocarbenium ions and carbodiimides, all the studied reactions, except for reaction d, proceed by charge-controlled stepwise pathways and FMO-controlled concerted pathways. The activation barrier of the cycloaddition are positively correlated to the transferred charge and second-order perturbative estimates of the stabilization energy of the complex COM1, but negatively correlated to the relative energies of the complex COM1on potential energy surfaces. The regioselectivity for the polar1,3-dipolar cycloaddition reactions of azocarbenium ions and carbodiimides is correctly predicted by local version of HSAB principle. For the charge-controlled stepwise pathways, the rigid structure of complex COM2is responsible for the high stereoselectivity. And for the FMO-controlled concerted pathways, the Woodward-Hoffmann rule determined the regio-stereoselectivity of products3. In chapter4, the polar1,3-dipolar cycloaddition and subsequent [1,2]-shift reactions between azocarbenium ions and acetylenes were studied and in this section we focused on the mechanism of the [1,2]-shift reactions and the substituent effect which is the prime ingredient in the distribution of the final products. Thus, including the model reaction,7categories and25kinds of[1,2]-shift reactions were examined. It indicated that the process from five-membered heterocycles3to4/5is proved to be a kinetically controlled[1,2]-shift reaction, the activation barrier determine the distribution of the final products4/5. The kind of migrating group can influence the regioselectivity of [1,2]-shift reactions. When the migrating group is Me, Et,i-Pr and Cl respectively, the interaction between five-membered ring and migrating group in separated pathways determinates the target for migration (N2or C4). For the different alkyl migrating group, the order of relative reactivities of [1,2]-shift reactions is as follow:i-Pr>Et>Me.In chapter5, the summary of reactions between1,3-dipolar azocarbenium ions and dipolarophile system (acetylenes, carbodiimides, nitriles, isocyanates and olefins) indicates that, the regioselectivity for polar1,3-dipolar cycloaddition between azocarbenium ions and dipolarophiles is correctly predicted by local version of HSAB principle. When dipolarophiles are triple bond compounds such as acetylenes and nitriles, both transition states of two different pathways (2-position shift or4-position shift) can exist on the potential energy surfaces in gas phase. Solvent effect affects the [1,2]-shift reactions dramatically and the final product4(2-position shift) is favored. While when dipolarophiles are double bond compound such as carbodiimides and isocyanates, the transition states of4-position shift were not located on the potential energy surfaces in gas phase, the migrating groups shift to the neighbor N2positin. For the [1,2]-shift reaction e (olefins), there is only one migration target (N2) to afford the final product4. For the different alkyl migrating group, the order of relative reactivities in [1,2]-shift reactions a-e are as follow: i-Pr>Et>Me.