Theoretical study of 1-methoxy-2-sulfanylethan-1-yl cation: Insight into intermediates in glycosidation reactions
Theoretical study of 1-methoxy-2-sulfanylethan-1-yl cation: Insight into intermediates in glycosidation reactions
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DOI：
10.1021/jo981944y
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发表时间：
1999-02-19
影响因子：
3.6
通讯作者：
Hoffmann, MR
中科院分区：
文献类型：
--
作者：
Dudley, TJ;Smoliakova, IP;Hoffmann, MR
报道了与 1-烷氧基-2-(芳基硫基)烷基卤化物和 2-(芳基硫基)吡喃糖基卤化物的亲核攻击中间体相关的两种模型化合物的平衡结构和谐振频率。使用 6-31G(d) 基组对两个模型离子中较大的 2-硫基四氢吡喃-1-基阳离子进行 Hartree-Fock (HF) 和二阶 Moller-Plesset (MP2) 计算。使用三重分裂价 6-311G(d,p) 基组和二次构型相互作用（包括单电子和双电子激发 (QCISD)）方法进一步研究了较小的模型离子 1-甲氧基-2-硫基大于-1-基阳离子。将模型离子中的局域原子电荷与氧鎓和表锍中的相应位点进行比较。对模型离子的研究表明，尽管硫对于立体选择性至关重要，但中间体更像是氧鎓离子而不是表锍离子。高水平计算（QCISD(T)/- 和 CCSD(T)/6-311++G(d,p)）表明，先前未识别的质子转移第二中间体的能量高出 8.0-8.5 kcal/mol，可能参与反应机制。发现对应于该质子位移的单分子过渡态比 1-甲氧基-2-硫基-1-基阳离子高 27-29 kcal/mol。
Equilibrium structures and harmonic vibrational frequencies of two model compounds related to the intermediates of nucleophilic attack on 1-alkoxy-2-(arylsulfanyl)alkyl halides and 2-(arylsulfanyl) pyranosyl halides are reported. Hartree-Fock (HF) and second-order Moller-Plesset (MP2) calculations using the 6-31G(d) basis set were performed on the larger of the two model ions, 2-sulfanyltetrahydropyran-1-yl cation. The smaller model ion, 1-methoxy-2-sulfanylethan-1-yl cation, was further investigated with a triple split valence, 6-311G(d,p), basis set and with the quadratic configuration interaction, including single- and double-electron excitations (QCISD), method. Localized atomic charges in the model ions were compared to corresponding sites in oxonium and episulfonium. The studies of the model ions suggest that the intermediate is more like an oxonium ion than an episulfonium ion, although the sulfur is critical to the stereoselectivity. High-level calculations (QCISD(T)/- and CCSD(T)/6-311++G(d,p)) indicate that a previously unidentified proton-shifted second intermediate, located 8.0-8.5 kcal/mol higher in energy, may be involved in reaction mechanisms. The unimolecular transition state corresponding to this proton shift was found to be 27-29 kcal/mol above the 1-methoxy-2-sulfanylethan-1-yl cation.