Critical assessment of two classical synthetic methods for preparation of thiophene-substituted isoxazoles
作者:Gheorghe Roman
DOI:10.1007/s11164-013-1101-8
日期:2014.5
isolated from the reaction as the major product. Substitution of the β-bromine atom from a chalcone dibromides with a methoxy group by solvolysis occurred when no base was used. Mixtures of isomeric isoxazoles in which the isoxazole that had a 2-thienyl group at position 5 were always major components, were obtained in good yields from reaction of thiophene-containing 1,3-diketones with hydroxylamine hydrochloride
通过查尔酮二溴化物和 1,3-二酮与盐酸羟胺的反应在不同条件下形成噻吩取代的异恶唑进行了研究。在二溴化物查耳酮类似物与盐酸羟胺的反应中使用 KOH 作为碱以适中的产率产生异构异恶唑的混合物。用吡啶代替 KOH 仅提供可忽略量的异恶唑,中间体 2-bromoprop-2-en-1-one 作为主要产物从反应中分离出来。当不使用碱时,通过溶剂分解从查耳酮二溴化物中取代β-溴原子与甲氧基发生。通过含噻吩的 1 的反应以良好的收率获得异构异恶唑的混合物,其中在 5 位具有 2-噻吩基的异恶唑始终是主要成分,3-二酮与盐酸羟胺,与反应 pH 值无关。在低 pH 条件下,区域选择性比查耳酮二溴化物与盐酸羟胺反应所观察到的要差,但产率要好得多。在高 pH 条件下,产率与低 pH 条件下相当,3-芳基-5-(2-苯硫基)异恶唑的区域选择性略有提高,但对应于初始 1,3-二酮的二肟也以低产率产生:立体异构体的混合物。