【摘要】 在HF/6-31G(d)水平下,对吲哚(A)与亚烷基丙二酸二甲脂(B)的Michael加成反应的机理进行了从头算理论研究.计算结果表明,该反应的机理为:A+B→分子复合物→TS1→IM→TS2→产物.其中第一阶段由复合物经过渡态TS1生成中间体IM,是C—C键的形成阶段,该阶段的活化能垒较后一阶段要大,是该反应的决速步骤;第二阶段由IM经过渡态TS2生成产物,完成H迁移和C—H键的形成.反应过程中,底物分子中离域化的π键电子的相互作用,促进了C—C新键的形成,同时吲哚的共轭体系遭到部分破坏,而体系经H迁移使新的C—H键形成后,吲哚环的共轭体系又得到了恢复.在MP2/6-311+G(d,p)水平下,分别考虑乙醇和1,2-二氯乙烷的溶剂化效应,单点能计算结果显示,质子化溶剂对反应的影响较大,不仅降低了反应的能垒,且溶剂质子有可能参与了H迁移和C—H键的形成过程,这一结论与实验结果一致.更多还原

【Abstract】 HF calculations with 6-31G(d) basis set were used to investigate the Michael addition (also called Friedel-Crafts alkylation) reaction mechanism of indole (A) with dimethyl alkylidene malonate (B). The results show that this reaction can proceed through two transition states, A+B→complex→TS1→ M→TS2→product. At the first stage, the new C—C bond is formed. The calculated energy barriers of this step are 210.5 and 209.6 kJ/mol for the R- and S-configuration product, respectively; and the stage is predicted to be the rate-determining step. Whereas, at the second stage H-transfer from indole to malonate occurs with the formation of the new C—H bond, the energy barriers calculated for this step are 99.2 and 115.1 kJ/mol for the R- and S-configuration product, respectively. During the reaction processes, the transfer and interaction of the π electrons in the reactant molecules may play an important role in the cleavage of the old bond C=C and the formation of the new ones (C—C and C—H), and it is just because of the electron transfer that makes the reaction proceed. Besides these, the effects of the solvents of alcohol and 1,2-dichloroethane on the title reaction were also tested with the single point energy calculations under the MP2/6-311+G(d,p) level of theory using the polarized continuum model (PCM) implemented in the Gaussian 03 package. PCM results indicate that the energy barriers of the reaction are reduced in thepresence of solvents, and the proton of alcohol may greatly influence and also participate in the H-transfer process, thereafter making this stage be a rate-determining one in alcohol solvent, while the solvent dichloroethane has little influence on the reaction path compared with that taking place in gas phase. The calculated results are helpful to explain explicitly why the deuterated product can be formed in the reported experiment where this addition reaction took place in the CH3OD solvent.更多还原