Activated allylic compounds react with trithiazyl trichloride, (NSCl)3, to give 1,2,5-thiadiazoles 1 and isothiazoles 2. An allylic 2-substituent normally prevents formation of an aromatic 1,2,5-thiadiazole, and isothiazole formation becomes the major pathway. Simple allylic compounds are not very reactive towards (NSCl)3 but a terminal electron withdrawing group (CO2Et) enhances the reactivity. With unsymmetrical allylic compounds, isothiazole formation is regiospecific placing the more electron withdrawing group adjacent to the ring sulfur. 1,3-Diketones give 3-acyl-1,2,5-thiadiazoles; unsymmetrical 1,3-diketones give these thiadiazoles regiospecifically, explicable by cyclisation of an intermediate onto the more reactive carbonyl group. 1,4-Diketones give 3,4-diacyl-1,2,5-thiadiazoles; thus 1,2-dibenzoyl-ethane, -ethene and -ethyne all give 3,4-dibenzoylthiadiazole (40–44%). Many of these trithiazyl trichloride reactions provide attractive one-step routes to 1,2,5-thiadiazoles and isothiazoles.
活化的烯丙基化合物与三氮
吡啶三
氯化物(NSCl)3反应,生成1,2,5-
硫噁唑1和异
硫噁唑2。烯丙基的2-取代基通常会阻止形成芳香性的1,2,5-
硫噁唑,而异
硫噁唑的形成则成为主要途径。简单的烯丙基化合物对(NSCl)3的反应性并不强,但末端的电子吸引基团(CO2Et)可以增强其反应性。对于不对称的烯丙基化合物,异
硫噁唑的形成是区域特异性的,更强的电子吸引基团会与环中的
硫相邻。1,3-二酮可以得到3-酰基-1,2,5-
硫噁唑;不对称的1,3-二酮则会以区域特异性的方式生成这些
硫噁唑,这可以用中间体在更活泼的羰基上发生环化来解释。1,4-二酮生成3,4-二酰基-1,2,5-
硫噁唑;因此,1,2-二苯甲酰基
乙烷、
乙烯和
乙炔均会得到3,4-二苯甲酰基
硫噁唑(40-44%)。这些三氮
吡啶三
氯化物的反应提供了制备1,2,5-
硫噁唑和异
硫噁唑的有吸引力的一步合成途径。