THERMAL ELECTROCYCLIC REACTIONS OF 2-AZA-1,3-BUTADIENE DERIVATIVES - A NEW N-HETEROCYCLIC ANNELATION
THERMAL ELECTROCYCLIC REACTIONS OF 2-AZA-1,3-BUTADIENE DERIVATIVES - A NEW N-HETEROCYCLIC ANNELATION
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DOI：
10.1021/jo00174a036
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发表时间：
1983-01-01
影响因子：
3.6
通讯作者：
TAYLOR, G
中科院分区：
文献类型：
--
作者：
GOVINDAN, CK;TAYLOR, G
描述了一种通用的3步缩合序列，其最终得到3，4-二氢-2-喹啉和相关衍生物（3）。环化步骤通过热解1-芳基-2-氮杂-1，3-丁二烯类似物（2）完成，该类似物（2）显然经历连续的6 π-电子电环化和1，5-氢迁移反应，得到产物。共轭氮杂二烯，2，是由非共轭异构体，1的碱催化异构化。化合物1是通过芳烯基酮或醛与2-丙烯基-1-胺缩合制备的。研究了氮杂二烯链上取代基的空间效应以及环化反应中芳烃基的空间效应和电子效应。得出以下一般性结论：2的C = N末端上的烷基取代基R阻碍竞争性降解过程（从4-π-开始）。电子电环化）并提高产物3的产率; 2的Ar上的吸电子取代基或吸电子Ar基团提高环化产物的产率，但它们对反应赋予很少的区域选择性;区域选择性可以通过π. Ar中的键固定;电环化也用π-进行得很好。电子过剩的Ar基团2。杂环产物3的优选构象可以通过1H NMR光谱容易地推断。
A general, 3-step annelation sequence, which ultimately gives 3,4-dihydro-2-quinolines and related derivatives (3), is described. The cyclization step is accomplished by pyrolysis of a 1-arenyl-2-aza-1,3-butadiene analog (2) that apparently undergoes successive 6 .pi.-electron electrocyclization and 1,5-hydrogen migration reactions to yield the product. The conjugated azadienes, 2, are prepared by the base-catalyzed isomerization of the unconjugated isomers, 1. Compounds 1 are prepared by condensing arenyl ketones or aldehydes with 2-propenyl-1-amine. Steric effects of substituents on the azadiene chain and steric and electronic effects of the arenyl group on the cyclization step were studied. The following general conclusions were drawn: alkyl substituents R on the C.dbd.N terminus of 2 hinder a competing degradative process (commencing with a 4-.pi.-electron electrocyclization) and improve the yield of products 3; electron-withdrawing substituents on Ar of 2 or electron-withdrawing Ar groups enhance the yield of cyclized products, but they impart little regioselectivity to the reaction; regioselectivity may be imparted by .pi. bond fixation in Ar; electrocyclization also proceeds well with .pi.-electron excessive Ar groups on 2. The preferred conformation of the heterocyclic product 3 can be readily deduced by 1H NMR spectroscopy.