Synthesis of 3,4-Disubstituted Piperidines by Carbonyl Ene and Prins Cyclizations: Switching between Kinetic and Thermodynamic Control with Brønsted and Lewis Acid Catalysts
作者:Jodi T. Williams、Perdip S. Bahia、Benson M. Kariuki、Neil Spencer、Douglas Philp、John S. Snaith
DOI:10.1021/jo052532+
日期:2006.3.1
to cis and trans 3,4-disubstituted piperidines is described. Carbonyl ene cyclization of aldehydes 4a−e catalyzed by MeAlCl2 in refluxing chloroform afforded the trans piperidines 7a−e with diastereomeric ratios of up to 93:7, while aldehyde 4f afforded solely the cis product 6f, which was resistant to isomerization to the trans isomer. It was demonstrated for 4a that the cyclization catalyzed by a
描述了一种新的顺式和反式3,4-二取代哌啶方法。在回流的氯仿中,MeAlCl 2催化的醛4a - e的羰基烯环化反应提供了高达93:7的非对映异构体比例的反式哌啶7a - e,而醛4f仅提供了顺式异构体6f,对顺反异构体具有抗性异构体。对于4a,证明了在动力学控制下进行的多种路易斯酸在低温下催化的环化反应主要得到顺式哌啶6a。,并在升温时异构化为热力学上更稳定的反式哌啶7a。与此相反,环化王子4A - ë浓盐酸在CH催化2氯2在低温下,得到顺式的哌啶6A - Ë最多的非对映体比率,以> 98:2。这些环化反应的收率和非对映选择性可以通过使用HCl饱和的CH 2 Cl 2形成相应的氯化物,然后除去氨影响的HCl来改善。醛4f和4g在后一种条件下也以良好的产率环化。DFT计算(B3LYP / 6-31G(d))支持的机理研究表明,环化反应是通过具有显着碳正离子特性的机理进行的,顺式碳正离子比反