Bromide assisted addition of hydrogen bromide to alkynes and allenes
Bromide assisted addition of hydrogen bromide to alkynes and allenes
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DOI：
10.1039/a703569a
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
H. Weiss;K. M. Touchette
中科院分区：
文献类型：
--
作者：
H. Weiss;K. M. Touchette
将 0.1 M 溴化季铵添加到 20% 三氟乙酸的二氯甲烷溶液中会导致非共轭炔烃的反应速率大幅增加。初始溴乙烯产物进一步反应以提供异构的溴乙烯和二溴乙烯的混合物。然而，在高盐浓度下，副反应被阻止，并且仅发现最初的溴乙烯。与相应的烯烃加成相反，主要机制被认为涉及卤化物离子对酸-炔π-络合物的一步、协同、亲核攻击，直接产生乙烯基卤化物。还可以看到涉及顺式添加的次要路径。在所有盐浓度下，丙二烯产生大量重排产物，表明阳离子机制的显着参与。
The addition of 0.1 M quaternary ammonium bromide to a solution of 20% trifluoroacetic acid in methylene chloride causes a large rate increase in the reaction of non-conjugated alkynes. The initial vinyl bromide product reacts further to provide a mixture of isomeric vinyl bromides and dibromides. At high salt concentrations however, the secondary reactions are prevented and only the initial vinyl bromide is found. In contrast to the corresponding addition to alkenes, the predominant mechanism is proposed to involve a one-step, concerted, nucleophilic attack by halide ion upon an acid–alkyne π-complex which produces the vinyl halide directly. A minor path involving syn addition is also seen. At all salt concentrations, allenes produce significant amounts of rearrangement products suggesting the significant involvement of a cationic mechanism.