Divergent reactivities of o-haloanilides with CuO nanoparticles in water: a green synthesis of benzoxazoles and o-hydroxyanilides
作者:Nilufa Khatun、Srimanta Guin、Saroj Kumar Rout、Bhisma K. Patel
DOI:10.1039/c3ra46820h
日期:——
In the present study, three divergent reaction paths emerged when o-haloanilides were subjected to CuO nanoparticles in water. o-Halo (I, Br) phenylbenzamides in the presence of CuO nanoparticles and Cs2CO3 in water at 100 °C provided o-hydroxyphenyl benzamides as the major product. However, a complete change in selectivity was observed in the presence of an organic base/ligand (TMEDA), giving 2-arylbenzoxazole as the exclusive product. The above selectivities were not clearly distinct when the corresponding alkylamides were treated either in the presence or absence of the ligand. A number of o-halophenyl alkylamides provided either exclusively o-dehalogenated products or a mixture of o-dehalogenated and o-hydroxylated products, but none gave 2-alkylbenzoxazoles. In addition to the above selectivities, the use of an environmentally friendly solvent (water) and base, and the recyclability of the catalyst make this procedure a benign alternative to the existing methods for the synthesis of these molecules, viz. o-hydroxybenzamides and o-arylbenzoxazoles.
在本研究中,当邻卤代苯甲酰基在水中与纳米 CuO 颗粒发生反应时,出现了三种不同的反应路径。邻卤代(I,Br)苯基苯甲酰胺在纳米 CuO 颗粒和 Cs2CO3 的存在下于 100 ℃ 的水中发生反应,主要产物为邻羟基苯基苯甲酰胺。然而,在有机碱/配体(TMEDA)的存在下,选择性发生了完全的变化,2-芳基苯并恶唑成为唯一的产物。在配体存在或不存在的情况下处理相应的烷基酰胺时,上述选择性没有明显的区别。一些邻卤苯基烷基酰胺只提供邻卤化产物或邻卤化和邻羟化产物的混合物,但没有一种烷基烷基酰胺提供 2-芳基苯并恶唑。除上述选择性外,由于使用了环保溶剂(水)和碱,以及催化剂的可回收性,使该方法成为合成这些分子(即邻羟基苯甲酰胺和邻芳基苯并恶唑)的现有方法的良性替代品。