Theoretical study on the lithium-halogen exchange reaction of 1,1-dihaloalkenes with methyllithium and the nucleophilic substitution reaction of the resulting α-halo alkenyllithiums
Theoretical study on the lithium-halogen exchange reaction of 1,1-dihaloalkenes with methyllithium and the nucleophilic substitution reaction of the resulting α-halo alkenyllithiums
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DOI：
10.1021/jo0519662
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发表时间：
2006-03-03
影响因子：
3.6
通讯作者：
Ando, K
中科院分区：
文献类型：
--
作者：
Ando, K
在6-31 +G*基集下，利用理论的B3LYP和MP2水平确定了1,1-二溴烯烃与甲基锂交换反应的过渡结构。与甲基锂二聚体的反应结果相似，但活化能较低。这些计算正确地预测了动力学和热力学的立体选择性。这是。在动力学条件下，1,1-二溴烯烃中受空间约束的溴原子主要与烷基锂（二聚体）反应。研究了4,4-二溴-3-甲基-3-戊烯醇在甲基锂存在下的分子内取代反应。醇的去质子化和锂-溴交换反应后，发生分子内取代反应，以一致的方式生成二氢呋喃。还研究了a-氯烯基锂与甲基锂的分子间取代。在甲基锂的存在下，3-（邻溴苯基）-1,1-二溴-1-丙烯的独立衍生物以类似的方式形成。溴苯与甲基锂的锂-溴交换反应为S(N)2反应，溶剂起重要作用。
Transition structures for the lithium-bromine exchange reaction of 1,1-dibromoalkenes with methyllithium have been located by both the B3LYP and the MP2 levels of theory with the 6-31 +G* basis set. The reaction with methyllithium dimer gave similar results with lower activation energies. These calculations predict both the kinetic and the thermodynamic stereoselectivity correctly. That is. the sterically more constrained bromine atom of 1,1-dibroinoalkenes was predominantly reacted with alkyllithium (dimer) in the kinetic condition. The intramolecular substitution reaction of 4,4-dibromo-3-methyl-3-pentenol in the presence of methyllithium has been investigated. After deprotonation of the alcohol and the lithium-bromine exchange reaction, the intramolecular substitution reaction occurs to give dihydrofuran in a concerted manner. The intermolecular substitution of a-chloro alkenyllithium with methyllithium was also studied for comparison. The formation of the indene derivative from 3-(o-brornophenyl)-1,1-dibromo-1-propene in the presence of methyllithium occurs in a similar manner. The lithium-bromine exchange reaction of bromobenzene with methyllithium occurs in an S(N)2 mechanism and the solvent plays an important role.