Li Hongbin, Petersen Jeffrey L, Wang Kung K
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506-6045, USA.
J Org Chem. 2003 Jul 11;68(14):5512-8. doi: 10.1021/jo020760n.
Thermolysis of the enyne-carbodiimides 7 having the central carbon-carbon double bond incorporated as part of the cyclopentene ring favors the formation of the corresponding N,4-didehydro-2-(phenylamino)pyridine intermediates, either as the sigma,pi-biradicals 8 or as the zwitterions 8', for subsequent synthetic elaborations. By placing appropriate substituents at the acetylenic terminus, a variety of the intramolecular decay routes are available for the initially formed sigma,pi-biradicals/zwitterions, leading to the 5,6-dihydrobenzo[c][1,8]naphthyridine 21, the 1,2,3,4-tetrahydro[1,8]naphthyridine 24 and related compounds 25 and 26, the 5,6-dihydrobenz[f]isoquinoline 28, and the benzofuro[3,2-c]pyridine 30. Surprisingly, the use of the dimethylamino group of the 2-(dimethylamino)phenyl substituent to capture the carbocationic center in the zwitterion 8e' furnished the 5H-pyrido[4,3-b]indole 32 in only 14% yield. 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 gel was converted to 32 in essentially quantitative yield. Thermolysis of the enyne-carbodiimide 42 having a methoxymethyl substituent at the acetylenic terminus led to the formation of 46' as a pyridine analogue of ortho-quinone methide imine. An intramolecular hetero-Diels-Alder reaction of 46' then furnished the tetrahydro[1,8]naphthyridino[2,1-c][1,4]benzoxazine 47.
将作为环戊烯环一部分并入的中心碳 - 碳双键的烯炔 - 碳二亚胺7进行热解，有利于形成相应的N,4 - 二脱氢 - 2 -（苯基氨基）吡啶中间体，其可以是σ,π - 双自由基8或两性离子8'，用于后续的合成修饰。通过在炔端基处引入适当的取代基，最初形成的σ,π - 双自由基/两性离子有多种分子内衰变途径，导致生成5,6 - 二氢苯并[c][1,8]萘啶21、1,2,3,4 - 四氢[1,8]萘啶24以及相关化合物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。令人惊讶的是，使用2 -（二甲基氨基）苯基取代基的二甲氨基捕获两性离子8e'中的碳正离子中心，仅以14％的产率得到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％的产率分离得到。然而，通过在5当量的二甲基苯基硅氯存在下对烯炔 - 碳二亚胺7e进行热解，可以使反应转向生成32。在该反应条件下，以86％的产率分离得到2 - 吡啶酮亚胺37，其在暴露于硅胶时基本上以定量产率转化为32。在炔端基处具有甲氧基甲基取代基的烯炔 - 碳二亚胺42的热解导致形成46'，其为邻醌甲基亚胺的吡啶类似物。然后46'的分子内杂 - Diels - Alder反应提供了四氢[1,8]萘啶并[2,1 - c][1,4]苯并恶嗪47。
