Synthesis and Photodimerization of 2-and 2,3-Disubstituted Anthracenes: Influence of Steric Interactions and London Dispersion on Diastereoselectivity
Synthesis and Photodimerization of 2-and 2,3-Disubstituted Anthracenes: Influence of Steric Interactions and London Dispersion on Diastereoselectivity
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DOI：
10.1021/acs.joc.9b01317
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发表时间：
2019-08-16
影响因子：
3.6
通讯作者：
Bettinger, Holger F.
中科院分区：
文献类型：
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作者：
Geiger, Thomas;Haupt, Anne;Bettinger, Holger F.
越来越多的证据表明，在有机、有机金属和无机化学中，由于伦敦弥散相互作用，大团的影响不仅是排斥的，而且可能是吸引的。研究了蒽的2- '和2,3位上的伯烷基取代基的大小对[π (4s) + π (4s)]光致二聚化非对映选择性（抗与同步二聚体）的影响。通过2,3-二溴蒽与烷基硼酸的Suzuki-Miyaura反应，以及由2,3-二取代1,3-丁二烯和萘醌还原得到的蒽醌，然后脱氢，合成了蒽衍生物。用x射线晶体学和核奥弗豪瑟效应光谱分析了二蒽同分异构体混合物的反/同形比。2,3-二甲基蒽的反同分异构体和正同分异构体的生成量相等，而在所有其他情况下，反二聚体是主要产物。空间尺寸（Charton参数）与同分异构体比呈线性相关（R-2 = 0.98），表明选择性主要受经典排斥性空间效应支配。异丁基取代基是一个例外，它产生的syn异构体的量增加。有人认为，这是由于伦敦色散相互作用的高度效应。
There is increased evidence that the effect of bulky groups in organic, organometallic, and inorganic chemistry is not only repulsive but can be attractive because of London dispersion interactions. The influence of the size of primary alkyl substituents in 2- ' and 2,3-positions of anthracenes on the diastereoselectivity (anti vs syn dimer) of the [pi(4s) + pi(4s)] photoinduced dimerization is investigated. The synthesis of the anthracene derivatives was achieved by Suzuki-Miyaura reaction of 2,3-dibromoanthracene with alkylboronic acids as well as by reduction of anthraquinones that were obtained from 2,3-disubstituted 1,3-butadienes and naphthoquinone followed by dehydrogenation. The mixtures of dianthracene isomers were analyzed with respect to the anti/syn-ratio of the products by X-ray crystallography and nuclear Overhauser effect spectroscopy. While for the 2,3-dimethylanthracene the anti and syn isomers were formed in equal amounts, the anti dimers are the major products in all other cases. A linear correlation (R-2 = 0.98) between the steric size (Charton parameter) and the isomeric ratio suggests that the selectivity is dominated by classical repulsive steric effects. An exception is the iso-butyl substituent that produces an increased amount of the syn isomer. It is suggested that this is due to an exalted effect of London dispersion interactions.