Triflic acid-catalyzed adamantylation of aromatics in [BMIM][OTf] ionic liquid; synthetic scope and mechanistic insight
作者:Kenneth K. Laali、Viorel D. Sarca、Takao Okazaki、Aaron Brock、Paul Der
DOI:10.1039/b416997b
日期:——
A mild and efficient process has been developed for the one-pot adamantylation of aromatic substrates employing 1-AdaOH, 1-AdaCl, 1-AdaBr, and 1-Br-3,5,7-trimethyladamantane as adamantylating agents, with triflic acid (TfOH) as promoter and n-butylmethylimidazolium triflate [BMIM][OTf] room temperature ionic liquid (IL) as solvent. The influence of reaction temperature, reaction time and the amount of TfOH was gauged in model reactions employing 1-AdaOH, 1-AdaCl and 1-AdaBr with toluene as the substrate. Under optimal conditions, the reactions exhibit high para selectivity with little or no adamantane side-product being formed. The synthetic scope of this transformation was tested for representative alkylbenzenes and haloalkylbenzenes. Comparative reactions carried out in 1,2-dichloroethane (DCE) produce increased amounts of the meta isomer and substantial amounts of adamantane. Substrate selectivities (KT/KB) were measured in competitive experiments in [BMIM][OTf] and in DCE as solvents. Isomerization tests were performed to shed light on the origin of the meta isomer. A DFT study was also conducted to compare relative stabilities of the isomeric products, to gauge the relative stabilities of the intermediate isomeric benzenium ions of adamantylation and their charge distribution modes, and to explore the intramolecular process for isomerization in the benzenium ion.
开发了一种温和高效的方法,使用 1-AdaOH、1-AdaCl、1-AdaBr 和 1-Br-3,5,7-三甲基金刚烷作为金刚烷基化剂,用三氟甲磺酸 ( TfOH)作为促进剂,正丁基甲基咪唑鎓三氟甲磺酸盐[BMIM][OTf]室温离子液体(IL)作为溶剂。在使用 1-AdaOH、1-AdaCl 和 1-AdaBr 以甲苯为底物的模型反应中测量了反应温度、反应时间和 TfOH 量的影响。在最佳条件下,反应表现出高对位选择性,几乎不形成金刚烷副产物或不形成金刚烷副产物。针对代表性烷基苯和卤代烷基苯测试了该转化的合成范围。在 1,2-二氯乙烷 (DCE) 中进行的对比反应产生增加量的间位异构体和大量金刚烷。底物选择性 (KT/KB) 在 [BMIM][OTf] 和 DCE 作为溶剂的竞争性实验中进行测量。进行异构化测试以揭示间位异构体的起源。还进行了DFT研究,比较了异构产物的相对稳定性,测定了金刚烷基化的中间异构体苯离子的相对稳定性及其电荷分布模式,并探索了苯离子异构化的分子内过程。