Horner,-the Wadsworth-emmons Reaction Mechanism

α,β-unsaturated carbonyl compounds, namely, conjugated unsaturated carbonyl compounds in organic synthesis plays an important role, but also in a multi-vinyl synthesis of natural products has also been widely used. In fact they can occur not only occurring carbon-oxygen double bond of 1, 2 - nucleophilic addition, but also carbon-carbon double bond of 1, 2 - electrophonic addition, and the entire conjugated system of 1, 4 - conjugate addition.α,β-unsaturated carbonyl compounds can also occur Michael addition reaction with the donor which can provide nucleophilic carbanion, and some also can occur Rauhut-Currier reaction (dimerization) and Nazarov cyclization reaction. It was mainly to use Witing reaction to productα,β-unsaturated carbonyl compounds; there are also regioselectivity, stereo selectivity and the rigorous for the reaction conditions in the preparation. So it is worth for the chemists to do further exploration of the research for producingα,β-unsaturated carbonyl compounds in organic synthesis.In the many preparation methods ofα,β-unsaturated carbonyl compounds, Horner-Wadsworth -Emmons (HWE) reaction takes up the leading position. So-called HWE reactions are mainly refers to a kind of reaction to produce olefins by aldehyde and phosphonate. Its advantage is a very good regioselectivity and stereo selectivity, and it is mainly to form thermodynamics to the stability of threo products in the reaction conductions.Though, there are many studies about Horner-Wadsworth-Emmons (HWE) reaction, but primarily an intervention study of organic compound, in regard to compare their rates of Z style and E style. And about the response mechanisms was largely speculation. So far the detailed theoretical studies about the mechanism were reported rarely. Therefore it is a very meaningful task on a more detailed study of the response mechanisms in quantum chemistry methods through the greater group theory.Comprehensive the above, we did many system studies for Horner-Wadsworth-Emmons response mechanisms, the influence of the replace base and the solvent and geometrical selectivity with HF and B3LYP methods in quantum chemistry methods. The thesis consists of five parts as follows:1. A study for the response mechanism of the HWE reaction Density functional theory (DFT) has been used to study the mechanism of the HWE reaction (formaldehyde and phosphonate carbanion) at the B3LYP/6-31G (d, p) levels. The transition states and the energy barriers of the reactions are obtained. We found that HWE reaction could react in both the free anionic system and the neutral system. The specific response mechanisms are shown as follow:(1)The response mechanisms of the HWE reaction which react in the free anionic system:We knew that the ring closure of an oxyanion to an oxaphosphetane (the first step of the reaction) is rate-determining step by the quantum calculation, and the energy barrier of the first step is 23.09 KJ/mol higher than the energy barrier of the second step.(2)The response mechanisms of the HWE reaction which react in the neutral system:Through calculation, the whole reaction occurs in three steps, the activation energy of the second step which is the rate-determining step of HWE reaction is 140.77 KJ/mol in the neutral system.2. A study for the geometrical selectivity of the HWE reactionWe did a study for the geometrical selectivity of HWE reaction in the free anionic system and the neutral system at the B3LYP/6-31G (d, p) levels. We did a detailed study for the response mechanism of each reaction, have obtained the transition states and the energy barriers of each reaction, and discussed the stability of the intermediates and the products. The results indicate that HWE reaction is mainly to form thermodynamics to the stability of threo products in the both system, and they are in accordance with the results of the organic synthesis.3. The effect of the subsistent on the HWE reactionBecause the HWE reaction is occurred by the formaldehyde and phosphonate carbanion, we do the study of the effect of the subsistent as follow:(1)We use the CN and NH2 to instead of an H of formaldehyde in order to compare the effect to the HWE reaction of the different polarity of the regiment at the B3LYP/6-31G (d, p) levels. The calculations show that the strong electron-withdrawing group CN and the strong electron-donating group NH2 have an effect on the stereochemistry of the HWE reaction, both of which lead to Z-products especially the strong electron-withdrawing groups are practically lead to only Z-products.(2)At the B3LYP/6-31G (d, p) levels, we use the cyan group and the ethynyl to replace the ester of the phosphonate, to compare the effect of the different subsistent. The results indicate that the HWE reaction which the both subsistent participate also has good selective, and the E- olefins is majority.4. The effect of the solvent on the HWE reactionWe do the study of the reaction which is urred by aldehyde and phosphonate carbanion in the solvent such as tetrahydrofuran, methanol and acetonitrile at the B3LYP/6-31G (d, p) levels. The results indicate that the reactions occur more easily in the solvent than in the gas.