芳基硼酸和芳基硼酸酯是有机合成中最重要的合成砌块之一了，它们的用途多种多样，更可以说是丰富多彩了，可以进行Suzuki偶联，Chan-Lam偶联，与不饱和化合物的1,2-加成，1,4-加成反应等等。此外，硼酸酯还可以转化为其它官能团如羟基，卤代物等等。因此，芳基硼酸酯的合成方法也是有很多的，比如钯催化的通过联硼酸频哪酯和卤代芳烃发生钯催化偶联反应制备了相应的芳基硼酸酯，以及金属锂试剂与卤代芳烃的金属化反应等等。今天为大家介绍芳胺氨基直接转变为硼酸酯，不需要先把氨基转变为卤素，再转变为硼酸酯，反应简洁高效。

芳基硼酸或硼酸酯的合成总结如下（图1）。

图1:芳基硼酸和芳基硼酸酯合成。图片来源:J. Org. Chem.

2012年，来自北京大学的Wang团队报道了如图2所示反应体系可直接将芳胺直接变芳基硼酸酯（图2）。

图2:反应通式。图片来源:J. Org. Chem.

该反应体系底物范围很广，产率最高可达到77%（图3-图6）。

图3:底物拓展。图片来源:J. Org. Chem.

图4:底物拓展。图片来源:J. Org. Chem.

图5:底物拓展。图片来源:J. Org. Chem.

图6:底物拓展。图片来源:J. Org. Chem.

可能的反应机理如图7所示。

图7:反应机理。图片来源:J. Org. Chem.

实验一般操作步骤如下：

B2pin2 (279 mg, 1.1 mmol) and 2-aminobenzonitrile (1aa, 118 mg, 1.0 mmol) were weighed in a 25 mL round-bottom flask. MeCN (3 mL) and t-BuONO (2a, 155 mg, 1.5 mmol) were then added in succession. The resulting reaction solution was stirred for 2 h at 80 °C (N2 evolution completed within 5 to 15 min). The solution was then concentrated under reduced pressure, and the crude residue was purified by flash chromatography (silica gel, petroleum ether/EtOAc = 200:1). 2- (4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)benzonitrile (4aa).

芳基硼酸酯构建最经典的方法当属Miyaura反应了（图1）。

图1：Miyaura Boration

芳基重氮盐是有机合成中非常常见的一类合成砌块，其在过渡金属如钯或铜，或光催化条件下与联硼酸频那醇酯可转化为芳基硼酸酯类化合物（图2）。

图2：芳基重氮盐转化为硼酸酯

若能开发操作简单并且绿色的方法由芳胺合成芳基硼酸酯显得更实用，2014年来自西安陕西师范大学的Dong Xue团队报道了一个甲醇促进的无金属参与的芳胺的硼酯化反应或硼酸化反应，反应体系底物普适性很广，操作也非常简单（图3和图4）。

图3：芳基重氮盐转化为硼酸酯

图4：芳基重氮盐转化为硼酸

作者提出了如图5的反应机理（图5）。

图5：反应机理

硼酸酯制备实验一般操作步骤如下：

To a solution of arylamine (0.5mmol, 1.0 equiv) in MeOH (1.0 mL) was added HCl (0.5 mL, 1.5 mmol, 3.0 equiv) followed by H2O (0.5 ml). This mixture was stirred 2 min, and the NaNO2solution (0.25 mL) was then added. The NaNO2 solution was prepared by dissolving 35 mg of NaNO2in H2O (0.25 mL). This mixture was stirred 30 min at 0–5 °C followed by B2pin2(2, 381 mg, 1.5 mmol, 3.0 equiv) in MeOH (1.0 mL). Thismixture was stirred 60 min. H2O (10 mL) was added to the reaction mixture, then extracted with CH2Cl2(50 mL, 3×). The combined organic layers were washed with sat. NaHCO3, dried over Na2SO4, followed by evaporation, and the crude residue was purified by flash chromatography.

硼酸制备实验一般操作步骤如下：

To a solution of arylamine (0.5mmol, 1.0 equiv) in MeOH (1.0 mL) was added HCl (0.5 mL, 1.5 mmol, 3.0 equiv), followed by H2O (0.5 ml). This mixture was stirred 2 min, and the NaNO2solution (0.25 mL) was then added. The NaNO2solution was prepared by dissolving 35 mg of NaNO2in H2O (0.25 mL). This mixture was stirred 30 min at 0–5 °C, followed by HCl (135 mg, 1.5 mmol, 3.0 equivalents) in MeOH (1.0 mL). This mixture was stirred 60 min. H2O (10 mL) was added to reaction mixture, then extracted with CH2Cl2(50 mL, 3×). The combined organic layer was dried over Na2SO4, followed by evaporation to give the products.

（1）J. Org. Chem., 2013, 78 (5), pp 1923–1933. 

（2）Synlett 2014, 25, 1577–1584