Photochemistry of vinyl halides. Formation of benzofurans by photolysis of .beta.-(o-methoxyphenyl)vinyl bromides
Photochemistry of vinyl halides. Formation of benzofurans by photolysis of .beta.-(o-methoxyphenyl)vinyl bromides
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卤乙烯的光化学。
DOI：
10.1021/jo00339a012
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发表时间：
1981
影响因子：
3.6
通讯作者：
H. Taniguchi
中科院分区：
文献类型：
--
作者：
Tatsuo Suzuki;T. Kitamura;T. Sonoda;Shinjiro Kobayashi;H. Taniguchi
0,/3-双(邻甲氧基苯基)取代的乙烯基溴的光解产生苯并呋喃衍生物，其衍生自甲氧基对中间体乙烯基阳离子的分子内亲核攻击。在芳基取代的溴乙烯中，仅检测到一种苯并呋喃衍生物。然而，当取代基是氢或甲基时，形成两种异构苯并呋喃，一种通过未重排的乙烯基阳离子形成，另一种通过(邻甲氧基苯基)-重排的乙烯基阳离子形成。在亲核溶剂(即甲醇)中照射α-甲基-3，/3-双(邻甲氧基苯基)乙烯基溴没有产生溶剂掺入的产物。在对(邻甲氧基苯基)-取代的溴乙烯的光解中，观察到了环化和最初形成的乙烯基阳离子的重排之间的选择性-反应性关系。众所周知，卤乙烯的辐照会产生源自乙烯基自由基的产物作为反应性中间体。 1 然而，最近发现卤乙烯光解过程中也会产生离子中间体，即乙烯基阳离子。我们报道了在 1, 1-二芳基-2-卤代-乙烯 2 3 和 1,1-二芳基-2-卤代丙烯 3 的光解中，相应的乙烯基阳离子是通过乙烯基自由基对中的内部电子转移产生的，乙烯基自由基对最初是由碳-卤素键的均裂裂变形成的（式 1）。 McNeely 和 Kropp 报道了在脂环族乙烯基卤化物的光解中获得了溶剂掺入的产物，并提出乙烯基阳离子
Photolysis of 0,/3-bis (o-methoxyphenyl)-substituted vinyl bromides gave benzofuran derivatives which are derived from an intramolecular nucleophilic attack of the methoxyl group on an intermediate vinyl cation. With-aryl-substituted vinyl bromides, only one type of benzofuran derivative was detected. However, when the a substituent was a hydrogen or a methyl group, two isomeric benzofurans were formed, one via the unrearranged vinyl cationand the other via an (o-methoxyphenyl)-rearranged vinyl cation. Irradiation of a-methyl-/3,/3-bis-(o-methoxyphenyl) vinyl bromide in nucleophilic solvent, ie, methanol, did not result in solvent-incorporated products. In thephotolysis of/¡-(o-methoxyphenyl)-substituted vinyl bromides a selectivity-reactivity relationship between the cyclization and the rearrangement of the intially formed vinyl cation was observed.It is well-known that irradiation of vinyl halides gives products derived from vinyl radicals as the reactive in-termediates. 1 However, it was recently found that an ionic itermediate, ie, a vinyl cation, was also generated in the course of the photolysis of vinyl halides. We reported that in the photolysis of 1, 1-diaryl-2-halo-ethylenes2 3and l, l-diaryl-2-halopropenes3 the corre-sponding vinyl cations were generated by an internal electron transfer in the vinyl radical pairs which were initially formed by homolytic fission of the carbon-halogen bond (eq 1). McNeely and Kropp reported that sol-vent-incorporated products were obtained in the photolysis of alicyclic vinyl halides andsuggested that vinyl cations