Ooi Takashi, Takahashi Makoto, Yamada Masao, Tayama Eiji, Omoto Kiyoyuki, Maruoka Keiji
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan.
J Am Chem Soc. 2004 Feb 4;126(4):1150-60. doi: 10.1021/ja030552s.
A series of (2,7-disubstituted-1,8-biphenylenedioxy)bis(dimethylaluminum) (2) has been readily prepared in situ by treatment of the requisite 2,7-disubstituted-1,8-biphenylenediol (1) with Me3Al (2 equiv) in CH2Cl2 at room temperature; this primarily relies on the successful establishment of a new synthetic procedure of 1 starting from inexpensive m-anisidine. Evaluation of 2 as a bidentate organoaluminum Lewis acid has been performed by the reduction of ketonic substrates using Bu3SnH as a hydride source in comparison to the conventional monodentate Lewis acid dimethylaluminum 2,6-xylenoxide (11), uncovering the significantly high activation ability of 2 toward carbonyl. Particularly, (2,7-dimethyl-1,8-biphenylenedioxy)bis(dimethylaluminum) (2a) exerted the highest reactivity, which has also been emphasized in the Mukaiyama aldol reaction. The structure of the bidentate Lewis acid 2 was unambiguously determined by single-crystal X-ray diffraction analysis of 2g possessing a bulky 3,5-di-tert-butylphenyl substituent, revealing the rigid dimeric assembly in the solid state. The double electrophilic activation of carbonyl substrate by 2a has been supported by low-temperature 13C NMR analysis as well as theoretical study using the Gaussian 98 program. Moreover, unique stereoselectivity has been observed in the 2a-promoted Mukaiyama Michael addition, and highly chemoselective functionalization of carbonyl compounds in the presence of their acetal counterparts has been realized using 2a. Finally, the effectiveness of 2a for the activation of ether functionality has been demonstrated in the Claisen rearrangement of allyl vinyl ethers.
通过在室温下于二氯甲烷中用三甲基铝（2当量）处理所需的2,7-二取代-1,8-联苯二酚（1），可轻松原位制备一系列（2,7-二取代-1,8-联苯二氧基）双（二甲基铝）（2）；这主要依赖于从廉价的间甲氧基苯胺成功建立1的新合成方法。与传统的单齿路易斯酸二甲基铝2,6-二甲苯氧化物（11）相比，使用三丁基锡氢作为氢化物源还原酮底物，对2作为双齿有机铝路易斯酸进行了评估，发现2对羰基具有显著高的活化能力。特别地，（2,7-二甲基-1,8-联苯二氧基）双（二甲基铝）（2a）表现出最高的反应活性，这在 Mukaiyama 羟醛反应中也得到了强调。通过对具有庞大的3,5-二叔丁基苯基取代基的2g进行单晶X射线衍射分析，明确确定了双齿路易斯酸2的结构，揭示了固态下的刚性二聚体组装。2a对羰基底物的双亲电活化得到了低温13C NMR分析以及使用高斯98程序的理论研究的支持。此外，在2a促进的Mukaiyama迈克尔加成中观察到了独特的立体选择性，并且使用2a实现了在缩醛存在下羰基化合物的高化学选择性官能化。最后，在烯丙基乙烯基醚的克莱森重排中证明了2a对醚官能团的活化效果。
