Theoretical Study Of Metal Carbenoid Promoted Cyclopropanation Reactions With Ethylene And The Effect Of THF Solvent On The Reaction Pathways

Many natural and unnatural products containing cyclopropane groups have important biological activity and in an array of substances used as starting materials and intermediates in organic synthesis. This has motivated a large number of research groups to develop new and wide-range methods to produce cyclopropanated products. A reaction between iodomethylzinc iodide and an olefin that produces a cyclopropane compound was first reported by Simmons and Smith in 1958. This method is called the Simmons-Smith(SS) reaction. A great deal of work has been done to improve and develop alternative methods to produce similar active reagents. To our knowledge, there have been only a few theoretical computational study of the cyclopropanation reactions for the carbenoid species.In this paper, we choosed several typical reactions(Li, Cu and Sm carbenoid etc.) which have been carefully studied using quantum methods, obtained some interesting results.In the paper, on the basis of the molecular orbital theory, the tradition transition state theory as well as quantum chemistry theory, the systems choosed have been investigated using Density Functional (DFT) Methods, the Moller-Plesset correlation energy correction MPn, the coupled cluster CCSD(T) calculations, the time-dependent DFT method and the Natural Bond Orbital analysis. The structures of the reagents, the reaction products and the transition states along the reaction paths have been obtained, then obtained the reaction surfaces, the spectrum datum, the thermodynamic datum as well as the information of orbitals. The reaction mechanism has been argued deeply using these datum.The whole paper consists of seven chapters. Chapter 1 mainly reviews the evolution of cyclopropanation reaction of ethylene with metal carbenoid [Simmons-Smith(SS)reagent]. The second chapter summarizes the theory of quantum chemistry and calculation methods of this paper. The contents of the two chapters were the basis and background of our studies and offer us with useful and reliable quantum methods.In Chapter 3 and Chapter 4, the cyclopropanation reaction of ethylene with Samarium (II) carbenoid [Simmons-Smith(SS)reagent] are studied by means of the B3LYP hybrid density functional method.The geometries for reactants,the transition states and the products are completely optimized. All the transition states are verified by the vibrational analysis and the intrinsic reaction coordinate (IRQ calculations. The results show that all CH₃SmCH₂X(X=Cl,Br and I) react with ethylene are fast, and both methylene transfer and carbometalation pathways are same as the lithium carbenoid.however, CHaSinCH₂I react with ethylene is the fastest. The effect of THF solvent was investigated by explicit coordination of the solvent THF molecules to the Sm (II) center in the carbenoid.The results show that CH₃SmCH₂I/(THF)_n (n=0,1,2) carbenoid carbometalation barrier to reaction become systematically higher as more THF solvent is added. In contrast, the barrier via the methylene transfer pathways remains low.the cyclopropanation reactions are able to occur at low temperatures because of the lower barrier to reaction.In the fifth chapter, to further improve our understanding of the Samarium-promoted cyclopropanation reactions, the cyclopropanation of reaction of ethylene promoted with divalent samarium carbenoid GSmCH₂Cl were studied by means of B3LYP hybrid density functional method. The reaction proceed through two possible pathways: methylene transfer and carbometalation. The ClSmCH₂Cl carbenoid was found to be noticeably different in structure with more electrophilic character and higher chemical reactivity than the closely related classical Simmons-Smith (IZnCH₂I) carbenoid. The effect of THF solvent was investigated by explicit coordination of the solvent THF molecules to the Sm (II) center in the carbenoid. The ClSmCH₂Cl /(THF) n (where n=0,1, 2) carbenoid had systematically lower barriers to cyclopropanation reaction by methylene transfer pathway as more THF solvent added. The methylene transfer pathway was found to be favoured, with the barrier to reaction going from 44.71-63.62 kJ/mol for carbometalation pathway upon the addition of two THF molecule.In the sixth chapter, the cyclopropanation reaction of ethylene with copper carbenoid [Simmons-Smith(SS)reagent] are studied by means of the B3LYP hybrid density functional method/The geometries for reactants,the transition states and the products are completely optimized. All the transition states are verified by the vibrational analysis and the intrinsic reaction coordinate (IRC) calculations. The results show that both CH3CUCHCl₂ and CH₃CuCHI₂ react with ethylene are fast via the methylene transfer pathway and carbometalation pathway, and both processes are fast for the lithium carbenoid, but the reaction barriers for cyclopropanation of ethylene with GG1CH2G become lower via carbometalation pathway than methylene transfer pathway.In the seventh chapter, using ab initio theory , four possible geometries of CF₃Li and four transition states between them are optimized at G2MP₂ lever, Especially the transition states of isomerization are also found in the potential energy surface .Vibration frequence analysis calculation is oomplated to verify all the configurations. The characteristics of the different geometric configurations are discussed by means of structure analysis, population analysis , frontier orbital energy and dipole moment.