Nucleophilic reactions at the sulfur of thiiranium and thiirenium ions. New insight in the electrophilic additions to alkenes and alkynes. Evidence for an episulfurane intermediate
Nucleophilic reactions at the sulfur of thiiranium and thiirenium ions. New insight in the electrophilic additions to alkenes and alkynes. Evidence for an episulfurane intermediate
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DOI：
10.1021/ja984304l
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发表时间：
1999-04-28
影响因子：
15
通讯作者：
Pasquato, L
中科院分区：
文献类型：
--
作者：
Fachini, M;Lucchini, V;Pasquato, L
硫杂环六氯锑酸盐1a、3和5a-c以及具有环外S-R取代基（R = Me、Et、i-Pr）的硫杂环六氯锑酸盐6a-c和7a与二烷基二硫化物R "SSR"（R "= Me、Et且R"不等于R）在25 ℃下在CD 2Cl 2中反应，得到S-R "取代离子。反应速率受到硫和环碳上取代基的空间位阻的影响。t-2，t-3-二叔丁基-r-1-甲基硫杂环丙烷六氯锑酸盐（2）不反应，t-2-叔丁基-c-3-苯基-r-1-甲基硫杂环丙烷（5a）的反应速度比c-2，t-3-二叔丁基-r-1-甲基硫杂环丙烷离子（1a）快约100倍。动力学数据的分析表明，锍硫在环平面上从平行于C-C环键的方向受到二硫化物的攻击。这也是确保与硫杂环戊二烯或硫杂环戊二烯离子的LUMO最大重叠的方向（在RHF/3 - 21G *//RHF/3 - 21G * 水平下测定）。方法模态和最大轨道重叠的综合考虑表明，在锍硫的亲核取代不是一个S（N）2-类反应，而是通过一个中间体与环硫烷类结构发生。微观可逆性的原理将决定这也是不饱和C-C键的亲电亚磺酰化中的第一中间体。
The thiiranium hexachloroantimonates 1a, 3, and 5a-c and the thiirenium hexachloroantimonates 6a-c and 7a with exocyclic S-R substituent (R = Me, Et, i-Pr) react at sulfur with dialkyl disulfides R"SSR" (R" = Me, Et and R" not equal R) in CD2Cl2 at 25 degrees C to give S-R" substituted ions. The reaction rates are affected by the steric hindrance of the substituents at sulfur and at ring carbons. t-2,t-3-Di-tert-butyl-r-1-methylthiiranium hexachloroantimonate (2) does not react, and the t-2-tert-butyl-c-3-phenyl-r-1-methylthiiranium (5a) reacts about 100 times faster than the c-2,t-3-di-tert-butyl-r-1-methylthiiraniun ion (1a). The analysis of the kinetic data suggests that the sulfonium sulfur undergoes attack by the disulfide in the ring plane from a direction that is parallel to the C-C ring bond. This is also the direction which ensures the maximum overlap with the LUMO of thiiranium or:thiirenium ions (determined at the RHF/3-21G*//RHF/3-21G* level). The combined consideration of the approach modality and of the maximum orbital overlap suggests that the nucleophilic substitution at sulfonium sulfur is not an S(N)2-like reaction but occurs via-an intermediate with episulfurane-like structure. The principle of microscopic reversibility will dictate that this is also the first intermediate in the electrophilic sulfenylation of unsaturated C-C bonds.