Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones
作者:Robin Klintworth、Garreth L Morgans、Stefania M Scalzullo、Charles B de Koning、Willem A L van Otterlo、Joseph P Michael
DOI:10.3762/bjoc.17.170
日期:——
various bromomethyl aryl and heteroaryl ketones, underwent cyclization in the presence of silica gel to give ethyl 6-(hetero)aryl-2,3-dihydro-1H-pyrrolizine-5-carboxylates within minutes upon microwave heating in xylene at 150 °C. Instead of functioning as a nucleophile, the enaminone acted as an electrophile at its carbonyl group during the cyclization. Yields of the bicyclic products were generally above
通过N- (乙氧基羰基甲基)吡咯烷-2-硫酮与各种溴甲基芳基和杂芳基酮之间的 Eschenmoser 硫化物收缩制备多种N- (乙氧基羰基甲基)烯胺酮,在硅胶存在下进行环化,得到乙基 6-(杂)芳基-2,3-二氢-1H-吡咯嗪-5-甲酸酯在二甲苯中于 150 °C 下微波加热几分钟内即可生成。在环化过程中,烯胺酮在其羰基处充当亲电子试剂,而不是充当亲核试剂。双环产品的收率一般在75%以上。由 ( E )-2-[2-(2-氧代-2-芳基亚乙基)哌啶-1-乙酯生产 2-芳基-5,6,7,8-四氢中氮茚-3-甲酸乙酯的类似微波辅助反应[酰基]乙酸酯在非极性溶剂中失败,但在较低温度和微波功率下在乙醇中发生,尽管需要更长的时间。提出了一种可能的环化机制,并描述了二氢吡咯嗪核心中新产生的吡咯环的进一步官能化。