Boron trichloride/tetra-n-butylammonium iodide:: A mild, selective combination reagent for the cleavage of primary alkyl aryl ethers
Boron trichloride/tetra-n-butylammonium iodide:: A mild, selective combination reagent for the cleavage of primary alkyl aryl ethers
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DOI：
10.1021/jo9910740
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发表时间：
1999-12-24
影响因子：
3.6
通讯作者：
Coe, JW
中科院分区：
文献类型：
--
作者：
Brooks, PR;Wirtz, MC;Coe, JW
许多试剂通常用于裂解伯烷基芳基醚1，如BBr3、2 EtSNa/DMF、3 TMSI、4 py-HCl、5和HBr/AcOH。6,7硼基试剂对于这种转化是特别通用的，因为硼中心的刘易斯酸度和配体的亲核性质可以有效地控制（例如，2-溴- 1,3,2 -苯并二硼硼，8,9 -br - bbn， 9和Me2-BBr10）。我们在此报道了BCl3和无水n-Bu4NI的混合物是一种强大的试剂组合，可以在低温到室温下快速裂解伯烷基芳醚。单独的三氯化硼在低温下不能去除分离的芳基甲基，但在可能进行螯合的情况下非常有效。然而，当n-Bu4NI存在时（1.1当量），BCl3对伯烷基芳醚的反应性大大增强。所得到的组合试剂体系温和、普遍适用、操作简单，对多种底物的裂解效果优于BBr3。此外，该组合试剂在某些情况下提供选择性脱烷基作用。一个比较实例突出了BCl3/n-Bu4NI试剂体系的反应性。在Sun等人描述的程序中，用BBr3（3当量/CH2Cl2）裂解14个不同取代的二甲氧基氟苯（例如，1）。在环境温度下，该反应通常需要24-48小时，并且通常需要额外的BBr3（0.5当量）来完全驱动转化
A number of reagents are routinely used to cleave primary alkyl aryl ethers1 such as BBr3, 2 EtSNa/DMF, 3 TMSI, 4 py-HCl, 5 and HBr/AcOH. 6, 7 Boron-based reagents are particularly versatile for this transformation, as the Lewis acidity of the boron center and the nucleophilic nature of the ligands can be effectively manipulated (eg, 2-bromo-1, 3, 2-benzodioxaborole, 8 9-Br-BBN, 9and Me2-BBr10). We report herein that a mixture of BCl3 and anhydrous n-Bu4NI is a powerful reagent combination for the facile cleavage of primary alkyl aryl ethers at low to ambient temperatures. 11 Boron trichloride alone does not remove isolated aryl methyl groups at low temperatures, 12 although it is extremely effective when chelation is possible. 13 With n-Bu4NI present (1.1 equiv), however, BCl3 reactivity toward primary alkyl aryl ethers is greatly enhanced. The resulting combination reagent system is mild, generally applicable, and operationally simple, and it can provide results superior to those of BBr3 for the cleavage of numerous substrates. Furthermore, the combination reagent provides selective dealkylation in certain cases.A comparative example highlights the reactivity of the BCl3/n-Bu4NI reagent system. In procedures described by Sun et al., 14 variously substituted dimethoxyfluorobenzenes (eg, 1) were cleaved with BBr3 (3 equiv/CH2Cl2). The reaction typically requires 24-48 h at ambient temperatures, and additional BBr3 is often required (0.5 equiv) to completely drive the conversion