Competing acyl transfer and intramolecular O ? N acyl group migration from an isolable O-acylisourea
作者:Anthony F. Hegarty、Margaret T. McCormack、Kieran Brady、George Ferguson、Paul J. Roberts
DOI:10.1039/p29800000867
日期:——
of (16a) with the solvent [to give the urea (18)] occurs at all pH. In acid, reaction is between the protonated (16a) and water and in base between the free isourea (16a) and hydroxide ion. The O-acylisourea also undergoes rapid intermolecular acyl transfer to a variety of amines, although reaction between the free amine and protonated isourea was too slow to be observed. The implications of these results
的Ô -acylisourea(16A),其为模型所提出的中间在碳化二亚胺缩合,和被形成在的酰氯(15)与苯甲酸根离子反应,使用显示出X射线晶体学有ž -构型。晶体是单斜晶,空间群P 2 1 / c,在一个单元中具有四个分子,其尺寸为a = 15.732(3),b = 16.246(5),c = 7.628(1)Å,β= 108.94(1)°。通过直接方法解析结构,并通过全矩阵最小二乘计算将1 281个所观察到的反射的R值改进为0.044。苯甲酰基是反式的亚胺氮的孤对上,C N键的长度为1.286(6)Å。异脲未经催化处理(在25°C下,在1:4二恶烷-水中,μ= 1.0)中O → N酰基转移,在pH> 7的情况下生成N-酰基酰胺(17)。缓慢的步骤是Z → E异构化。在较低的pH(3–6)下,异脲的Z → E异构化(因此发生O → N酰基转移)被酸催化,但在pH