Photoinduced, ionic Meerwein arylation of olefins
Photoinduced, ionic Meerwein arylation of olefins
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DOI：
10.1021/jo010469s
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发表时间：
2001-09-21
影响因子：
3.6
通讯作者：
Albini, A
中科院分区：
文献类型：
--
作者：
Mella, M;Coppo, P;Albini, A
4-氯苯胺或其N，N-二甲基衍生物在极性溶剂中的照射产生相应的三重苯基阳离子。这些被烯烃捕获，以中等至良好的产率产生芳基化产物。B3 LYP计算表明，三重态阳离子滑动与乙烯的键合加合物的活化能可以忽略不计，而它只形成一个边缘稳定的CT复杂的水（选择作为一个代表性的西格玛亲核试剂）。最终产物的结构取决于加合阳离子与烯烃的优选路径。在芳基烯烃的情况下，其去质子化为芪衍生物，而从2，3-二甲基-2-丁烯和烯丙基三甲基硅烷，通过消除γ中的离电基团获得烯丙基苯胺。在单取代和二取代烯烃的情况下，阳离子加成氯而不是消除氯，得到β-氯烷基苯胺。通过加合物的酚鎓离子结构，可以最好地理解烯烃加成的区域和立体化学。以β形式进入的亲核试剂可以在加合物阳离子比起始苯基阳离子更有效地被捕获的条件下变化。因此，当在甲醇中进行照射时，形成β-甲氧基烷基苯胺。在硼氢化钠存在下，在含有碘化物和未取代的烷基苯胺的乙腈中得到β-碘代烷基苯胺。发现了4-戊烯酸的分子内亲核捕获现象。该反应是烯烃的自由基Meerwin芳基化的宽范围离子类似物。
Irradiation of 4-chloroaniline or of its NN-dimethyl derivative in polar solvents generates the corresponding triplet phenyl cations. These are trapped by alkenes yielding arylated products in medium to good yields. B3LYP calculations show that the triplet cation slides with negligible activation energy to a bonded adduct with ethylene, whereas it forms only a marginally stabilized CT complex with water (chosen as a representative sigma nucleophile). The structure of the final products depends on the preferred path from the adduct cation with the alkene. In the case of aryl olefins, this deprotonates to stilbene derivatives, while, from 2,3-dimethyl-2-butene and allytrimethylsilane, allylanilines are obtained by elimination of an electrofugal group in gamma. In the case of mono- and disubstituted alkenes the cation adds chloride rather than eliminating and beta -chloroalkylanilines are obtained. The regio- and sterochemistry of the addition across the alkene are best understood with a phenonium ion structure for the adduct. The nucleophile entering in beta can be varied under conditions in which the adduct cation is trapped more efficiently than the starting phenyl cation. Thus, beta -methoxyalkylanilines are formed when the irradiation is carried out in methanol. beta -Iodoalkylanilines are obtained in acetonitrile containing iodide and unsubstituted alkylanilines in the presence of sodium borohydride. A case of intramolecular nucleophilic trapping is found with 4-pentenoic acid. The reaction is a wide-scope ionic analogue of the radicalic Meerwin arylation of olefins.