Facile synthesis of highly functionalized six-membered heterocycles via PPh3-catalyzed [4+2] annulations of activated terminal alkynes and hetero-dienes: scope, mechanism, and application
作者:Qiongmei Zhang、Tong Fang、Xiaofeng Tong
DOI:10.1016/j.tet.2010.07.043
日期:2010.10
A novel [4+2] annulation between activated terminal alkynes and aza-dienes or oxo-dienes has been developed with the use of triphenylphosphine catalyst (20 mol %), which provides a facile method for synthesis of the corresponding highly functionalized dihydropyridines or dihydropyrans in good to excellent yields. The reaction mechanism has also been established, consisting formal hetero-Diels-Alder reaction catalyzed by PPh3 and [1,3]-proton transfer, which exhibits a large isotopic effect. (C) 2010 Elsevier Ltd. All rights reserved.
PPh3-catalyzed [2 + 2 + 2] and [4 + 2] annulations: synthesis of highly substituted 1,2-dihydropyridines (DHPs)
PPh3-catalyzed [2 + 2 + 2] annulations between two units of an activated terminal alkyne and one unit of an aryl N-tosylimine have been developed to provide a synthetic method for highly substituted dihydropyridines. On the basis of the mechanism of the [2 + 2 + 2] annulation, PPh3-catalyzed [4 + 2] annulations have also been discovered.