水催化2个酯分子相互转化反应的理论研究

Theoretical Studies on Water Catalysis of Two Esters Interconversion Reaction

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-acetoxymultiplolide(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.

Compounds 1 and 2 could interconverse to each other at room temperature when water was encoun-tered. 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 dra-matically decreased. Further results showed that the solvation effects of water also reduced the activation ener-gy. 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, re-spectively. 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 alco-holic intermediate.