Cascade Cyclizations via <i>N</i>,4-Didehydro-2-(phenylamino)pyridine Biradicals/Zwitterions Generated from Enyne−Carbodiimides
作者:Hongbin Li、Jeffrey L. Petersen、Kung K. Wang
DOI:10.1021/jo020760n
日期:2003.7.1
The majority of the products were the 1H-pyrrolo[2,3-b]quinolines 34 and 35, isolated in 48 and 7% yields, respectively. However, it was possible to redirect the reaction toward 32 by conducting thermolysis of the enyne-carbodiimide 7e in the presence of 5 equiv of dimethylphenylsilyl chloride. Under this reaction condition, the 2-pyridone imine 37 was isolated in 86% yield, which on exposure to silica
具有作为环戊烯环的一部分并入的中央碳-碳双键的烯炔-碳二亚胺7的热分解有利于形成相应的N,4-二氢-2-(苯基氨基)吡啶中间体,即sigma,pi-双自由基8或作为两性离子8',用于随后的合成修饰。通过在炔基末端放置适当的取代基,可以使用多种分子内衰变途径来形成最初形成的sigma,pi双自由基/两性离子,从而生成5,6-二氢苯并[c] [1,8]萘啶21, 1,2,3,4-四氢[1,8]萘啶24及相关化合物25和26、5,6-二氢苯并[f]异喹啉28和苯并呋喃[3,2-c]吡啶30。使用2-(二甲基氨基)苯基取代基的二甲基氨基捕获两性离子8e′中的碳阳离子中心,仅以14%的收率提供了5H-吡啶并[4,3-b]吲哚32。大多数产物是1H-吡咯并[2,3-b]喹啉34和35,分别以48%和7%的产率分离。然而,可以通过在5当量的二甲基苯基甲硅烷基氯的存在下进行烯炔-碳二亚胺7e的热解来将反应