3-(Dimethylboryl)pyridine: synthesis, structure, and remarkable steric effects in scrambling reactions.
3-(Dimethylboryl)pyridine: synthesis, structure, and remarkable steric effects in scrambling reactions.
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DOI：
10.1021/jo7018043
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发表时间：
2008-01
期刊：
影响因子：
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通讯作者：
S. Wakabayashi;S. Imamura;Y. Sugihara;M. Shimizu;T. Kitagawa;Y. Ohki;K. Tatsumi
中科院分区：
文献类型：
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作者：
S. Wakabayashi;S. Imamura;Y. Sugihara;M. Shimizu;T. Kitagawa;Y. Ohki;K. Tatsumi
本文报道了3-（二甲基硼基）吡啶（1a）的简便合成方法。化合物1a组装成刚性环状四聚体，其在结晶状态和溶液中均通过分子间硼-氮配位键稳定。与已报道的3-（二乙基硼基）吡啶（2a）（其为锥形构象）相比，1a的突出结构特征是其四聚体为1，2-交替构象。为了研究硼原子上的取代基对低聚物稳定性的影响，使用1，2和3-（二正丁基硼基）吡啶3进行了组分分子的加扰实验。虽然当四聚体的组分分子为2或3时，需要在80-90 ℃下加热20小时以达到扰乱反应的平衡，但1中的扰乱在相对温和的条件下进行（60 ℃，3小时）。与2或3所需的条件相比，1所需的反应条件的这种差异不能仅通过基于键长或THC的稳定性来解释。看来，虽然只有S（N）1型途径可能参与2或3的乱序，但在1的乱序反应期间，S（N）1和S（N）2型机制同时起作用，或者S（N）1和S（N）2之间的中间机制起作用，这得到了动力学研究和使用模型化合物的计算的支持。
A facile method for the synthesis of 3-(dimethylboryl)pyridine (1a) is described. Compound 1a assembles into a rigid cyclic tetramer stabilized via intermolecular boron-nitrogen coordination bonds both in the crystalline state and in solution. The outstanding structural feature of 1a, as compared with previously reported 3-(diethylboryl)pyridine (2a) (which adopts a cone conformation), is that the tetramer of 1a adopts a 1,2-alternate conformation. To investigate the effect of substituents at the boron atom on the stabilities of the oligomers, scrambling experiments of the component molecules using 1, 2, and 3-(di-n-butylboryl)pyridines 3 were carried out. Although heating at 80-90 degrees C for 20 h was required to attain the equilibrium of the scrambling reactions when the component molecules of the tetramers were 2 or 3, the scrambling in 1 proceeded under relatively mild conditions (60 degrees C, 3 h). This difference in reaction conditions required for 1, as compared to conditions required for 2 or 3, could not be explained solely by the stabilities based on bond lengths or THC. It appears that whereas only an S(N)1-type pathway may be involved in the scrambling of 2 or 3, both S(N)1- and S(N)2-type mechanisms operate simultaneously during scrambling reactions of 1 or an intermediate mechanism between S(N)1 and S(N)2 operates, which was supported by kinetic studies and calculations using model compounds.