Rapid, efficient, room temperature aromatization of Hantzsch-1,4-dihydropyridines with vanadium(V) salts: superiority of classical technique versus microwave promoted reaction
作者:Mirela Filipan-Litvić、Mladen Litvić、Vladimir Vinković
DOI:10.1016/j.tet.2008.08.103
日期:2008.11
The aromatization of 1,4-dihydropyridines (1,4-DHPs) employing group 4 (Zr and Hf) and 5 (V, Nb, Ta) elements of periodic system has been studied. The reaction with VOCl3 in dichloromethane at room temperature afforded products, substituted pyridines, in high-to-excellent yield. For the first time, the formation of charge-transfer complexes (CTCs) has been evidenced in preorganization step between
研究了使用周期系统的第4组(Zr和Hf)和第5组(V,Nb,Ta)元素对1,4-二氢吡啶(1,4-DHPs)进行的芳构化。在室温下与VOCl 3在二氯甲烷中的反应以高至优异的产率提供了产物,取代的吡啶。首次在电子转移之前的1,4-DHP和氧化剂之间的预组织步骤中证明了电荷转移络合物(CTC)的形成。仅在中性溶剂(如二氯甲烷)中形成四氯化碳,其特征是强烈的着色。V 2 O 5将1,4-DHP芳构化在无溶剂介质中,乙酸在回流中的作用优于微波促进的反应。唯一合理的解释是在V 2 O 5的聚合物结构中发现的,该结构缓慢转移了活化反应物所需的微波能量。已发现4-正丙基-1,4-DHP的溶剂极性依赖性氧化脱烷基。出乎意料的是,与在相同反应条件下在二氯甲烷中获得的91%相比,在乙酸中的反应仅提供33%的脱烷基化产物。