New facile experimental procedures for the preparation of 2,3,4,6-tetrasubstituted pyridines in a single synthetic step have been developed. Thus, an enamino ester and alkynone react by Michael additionâcyclodehydration in a heterocyclisation process that is catalysed by acetic acid, Amberlyst 15 ion exchange resin, zinc(II) bromide or ytterbium(III) triflate. The new one-step Brønsted or Lewis acid-catalysed BohlmannâRahtz reaction is a simple, direct and highly expedient method for the synthesis of pyridines that proceeds at a lower reaction temperature and avoids the need to isolate reaction intermediates.
新近开发了一种简便的实验程序,用于在单一合成步骤中制备2,3,4,6-四取代
吡啶。在此过程中,烯胺酯和炔酮通过迈克尔加成-环脱
水反应在杂环化过程中催化,催化剂可为
乙酸、Amberlyst 15离子交换
树脂、
锌(II)
溴化物或
镱(III)
三氟甲磺酸盐。这种新型的单步布伦斯特德或
路易斯酸催化Bohlmann-Rahtz反应,是一种直接、简单且高效的合成
吡啶的方法,其反应温度较低,且无需分离反应中间体。