Nitrobenzoxadiazoles and related heterocycles: a relationship between aromaticity, superelectrophilicity and pericyclic reactivity
作者:Sami Lakhdar、R?gis Goumont、Taoufik Boubaker、Malika Mokhtari、Fran?ois Terrier
DOI:10.1039/b602002j
日期:——
A study of the dual electrophilic and pericyclic reactivity of 4,6-dinitrobenzofurazan (DNBZ, 2), 4,6-dinitro-2,1,3-benzothiadiazole (DNBS, 3), 4,6-dinitro-2,1,3-benzoselenadiazole (DNBSe, 4) is reported. Kinetic and thermodynamic measurements of the ease of covalent hydration of 2-4 to give the corresponding hydroxy sigma-adducts C-2-C-4 have been carried out over a large pH range in aqueous solution
对4,6-二硝基苯并呋喃山(DNBZ,2),4,6-二硝基-2,1,3-苯并噻二唑(DNBS,3),4,6-二硝基-2,1,据报道3-苯并硒二唑(DNBSe,4)。在较大的pH范围内,在水溶液中进行了2-4共价水合的难易程度的动力学和热力学测量,得到了相应的羟基sigma-加合物C-2-C-4。数据分析允许确定与2-4对水的侵蚀敏感性有关的速率常数k1(H2O),以及sigma络合过程的pKa值。pKa值的范围从DNBZ的3.92到DNBSe的6.34到DNBS的7.86,这三个杂芳族化合物的亲电子特性都非常接近于超亲电子参比物,即4,6-二硝基苯并呋喃(DNBF,1; pKa = 3.75),比标准的Meisenheimer亲电子试剂1,3,5-三硝基苯(TNB,pKa = 13.43)更高。最重要的是,发现水是有效的亲核试剂,它对加合物C-2和C-4的形成有重要作用。这证实了先前的观察结果,即pKa值为ca。图8是使H