The Synthesis Of 2,4-dimethyl-5,6-dihydro-1,2-pyran And Research Of Ring-open Reaction

Methyl-pyran(2-methyl-5,6-dihydro-2H-pyran)is a kind of intermediate in many natural products and organic synthesis, especially for leaf alcohol(cis-3-hexene-1-ol).The reason is that the ring-open of methyl-pyran can ensure the product is a kind of cis structure, so it's essencial to make research on the synthesis of methyl pyran There are many kinds of methods for synthesizing methyl pyran, and in this paper, we select paraformaldehyde and piperylene as raw materials, and Lewis acid as catalyst for Diels-Alder reaction which has the advantages of high atom utilization and conversion rate and so on.According to the characteristics of the reaction, paraformaldehyde must be depolymerized before reacting with piperylene. Sothe depolymerization condition of paraformaldehyde was studied firstly. By means of the single factor experiment, many factors had been studied such as the kind of solvent, the heating time, the reaction time and the addition of sulfuric acid and so on. Eventually, we chose three factors which includes the heating time, the reaction time and the addition of sulfuric acid to make a response surface experiment design, and the optimal depolymerization conditions of paraformaldehyde were as follows: reaction temperature was 92.6 ?, the amount of H2SO4 added was 0.46%, heating time was 3.9 h, and the formaldehyde content after paraformaldehyde depolymerization under optimized condition was 21.1%.At the same time, we optimized the synthesis condition of methyl pyran in this paper. By means of the single factor experiment, we studied many factors such as the species and addition of catalyst, the reaction time, the reaction temperature and the molar ratio of solvent and piperylene and so on. At last, three factors were chosen which included the reaction temperature, the addition of catalyst and the molar ratio of solvent and piperylene to make a response surface experiment design, and the optimal depolymerization conditions of paraformaldehyde was obtained. The result were as follows: reaction temperature was 96.4?, addition of catalyst was 2.5ml, the molar ratio of solvent and piperylene was 1.55, and the optimized methyl pyran yield was 39.3%.Finally, the synthesis and ring opening of methyl pyran were researched by Gaussian simulation software. At first, we studied the effects of Levis acid on the synthesis of methyl pyran, and found that Lewis acid can form ligand with formaldehyde and lower molecular orbital energy by electron-withdrawing effect. And chose B3 LYP / 6-31 G in DFT as basic set, and used QST3 for searching the intermediates and transition states for synthesizing of methyl pyran, and we found that the synthesis of methyl pyran experienced one transition state. Secondly, we chose DFT in B3 LYP /6-31G** as the basic set, and used QST2 k for searching the intermediate and transition states of the ring-open of methyl pyan, and we found that the ring-open reaction experienced two transition states and one intermediate which provided some guidance for the real ring-open reaction of methyl pyran.