Total synthesis of structures proposed for quinocitrinines A and B and their analogs. Microwave energy as efficient tool for generating heterocycles
作者:Victoria Machtey、Hugo E. Gottlieb、Gerardo Byk
DOI:10.3998/ark.5550190.0012.923
日期:——
A first totalsynthesis of the structuresproposed for quinocitrinines A and B has been accomplished by a three steps strategy which also applies for the synthesis of non-natural analogs. In the first step a microwave assisted Friedlander condensation between a substituted oamino-benzaldehyde and a substituted tetramic acid generated intermediate fused tricyclic quinolines which were N-methylated using
为奎尼奇宁 A 和 B 提出的结构的第一次全合成已通过三步策略完成,该策略也适用于非天然类似物的合成。在第一步中,取代的邻氨基苯甲醛和取代的特拉姆酸之间的微波辅助弗里德兰德缩合生成中间体稠合三环喹啉,其使用三氟甲磺酸甲酯进行 N-甲基化。天然化合物是在使用 BBr3 从芳环上裂解 O-甲基后获得的。所有反应都受到内酰胺环中 C-11 的差向异构化的影响,将奎尼替林 A 转化为奎尼奇宁 B。为了减少差向异构化,优化分析是必要的。
Diastereofacial selectivity in reduction of chiral tetramic acids
The reduction of (5S)-5-alkyl-2,4-dioxopyrrolidines, so-called tetramic acids, by NaBH4 gives only partial diastereofacial selectivity in the case of the N-substituted analogues 9f-i, unlike the carbamate derivatives 9a-3 which give the reduced cis-pyrrolidinones 10betaa-e. Increasing the steric hindrance of either the N- or C-5-substituents enhances the re-face selectivity. On the other hand, reduction of the heterobicyclic compound 9n leads to a dramatic reversal of the stereoselectivity. Preliminary calculations show that the N-atom of the ring is slightly pyramidalized; the direction of hydride addition could be a consequence of this finding.
作者:Masood Hosseini、Henriette Kringelum、Anthony Murray、Janne E. Tønder
DOI:10.1021/ol060500i
日期:2006.5.1
Pyrrolidine-2,4-diones (1) are naturally occurring analogues of amino acids. We herein present a facile synthesis of N-acylated, O-alkylated pyrrolin-2-ones (2) in high yield and excellent enantiopurity. Molecular mechanics calculations suggest that the resulting dipeptide analogues adopt a linear, extended conformation.