水催化2个酯分子相互转化反应的理论研究

从印楝植物内生真菌Phomopsis sp.培养液中分离得到的4-acetoxymultiplolide(1)和1-acetoxymultiplo-lide(2)在室温及水存在下能够相互转化. 提出二者相互转化最可能的4个途径(机理A~D). 在B3LYP/6-311+G(d,p)水平进行气相条件的优化, 结果表明, 无水催化的机理A中TS1和TS2的活化能均显著大于120 kJ/mol, 2个分子水催化的机理D中TS1和TS2的活化能则显著降低. 计算结果显示水的溶剂化效应能进一步降低机理D中TS1和TS2的活化能. 在MP2/6-311++G(2d,2p)//B3LYP/6-311+G(d,p)水平计算了单点能, 得到在水相时机理D中TS1和TS2的活化能分别为106.24和107.37 kJ/mol. 因此, 机理D是化合物1 和2在室温下及水存在时相互转化最可能的途径, 该途径是一种特殊的水催化分子内酯的醇解反应, 也是一种经典的亲核加成反应, 通过一种新的叔醇中间体实现.

Theoretical Studies on Water Catalysis of Two Esters Interconversion Reaction†

Compounds 1 and 2 could interconverse to each other at room temperature when water was encountered. Four possible interconversion mechanisms, A, B, C and D, were put up. At B3LYP/6-311+G(d,p) level in gas phase, the optimized activation energies of TS1 and TS2 in mechanism A were all distinctively more than 120 kJ/mol. But as for mechanism D, the optimized activation energies of TS1 and TS2 were dramatically decreased. Further results showed that the solvation effects of water also reduced the activation energy. Meanwhile, the single point energy were calculated at MP2/6-311++G(2d,2p)//B3LYP/6-311+G(d,p) level. Finally the activation energies of TS1 and TS2 in mechanism D were 106.24 and 107.37 kJ/mol, respectively. Therefore, mechanism D was the most possible pathway for the interconversion between compounds 1 and 2 at room temperature. This preferred mechanism pathway was a special water-catalyzed intramolecular oxoester alcoholysis, which also was a conventional nucleophilic addition, producing a novel tetrahedral alcoholic intermediate.