An efficient synthesis of quinoline-2,5,8(1H)-triones bearing alkyl groups at C3 and/or C4 is described. The reaction sequence employed involves Knorr cyclization of 2,5-dimethoxyanilides into 5,8-dimethoxyquinoline systems, followed by oxidative demethylation with cerium ammonium nitrate. The starting 2,5-dimethoxyanilides were prepared by chemoselective acylation by regioselective alkylation of S-tert-butyl acetothioacetate (1) at C2 and/or C4. The introduction of electrophiles other than alkyl groups at C2 on 1 was also studied.
描述了一种高效合成在C3和/或C4位具有烷基取代基的
喹啉-2,5,8(1H)-三酮的方法。所采用的反应序列包括
2,5-二甲氧基苯胺的Knorr环化,形成
5,8-二甲氧基喹啉体系,随后用
铈铵硝酸盐进行氧化去甲基化。起始的
2,5-二甲氧基苯胺通过选择性酰化实现,根据S-叔丁基乙酰
硫代乙酸酯(1)在C2和/或C4位的区域选择性烷基化制备而成。还研究了在1的C2位引入除了烷基以外的电亲体。