Exploring Catalyst and Solvent Effects in the Multicomponent Synthesis of Pyridine-3,5-dicarbonitriles
作者:Kai Guo、Mark J. Thompson、Beining Chen
DOI:10.1021/jo901232b
日期:2009.9.18
protocol to overcome the difficulty in the direct synthesis of pyridine-3,5-dicarbonitriles via the MCR from sterically hindered aldehydes using either base was realized by changing the reaction solvent from ethanol to acetonitrile. Mechanistically, the two catalysts were found to each promote different pathways in the final oxidation step of the penultimate product, 1,4-dihydropyridine 6. A reaction
系统地研究了离子碱氢氧化四丁基铵(TBAH)和胺碱哌啶对使用醛,丙二腈和硫醇的多组分反应(MCR)直接合成吡啶3,5-二甲腈的影响。当在乙醇中进行MCR时,胺碱显示出更好的结果,而在乙腈中使用离子碱得到的收率相近,但反应时间却短得多。通过将反应溶剂从乙醇更改为乙腈,可以实现一种改进的方案,该方案可以克服使用任何一种碱通过MCR由位阻醛通过MCR直接合成3,5-二碳吡啶的困难。从机理上讲,发现两种催化剂在倒数第二个产物1,4-二氢吡啶的最终氧化步骤中各自促进不同的途径6。反应中间体Knoevenagel加合物7在胺碱催化的体系中起主要作用,而在存在离子碱的情况下,好氧氧气充当主要氧化剂。