PPh<sub>3</sub>-Catalyzed Reactions of Alkyl Propiolates with<i>N</i>-Tosylimines: A Facile Synthesis of Alkyl 2-[aryl(tosylimino)methyl]acrylate and an Insight into the Reaction Mechanism
A new PPh3‐catalyzed synthesis of alkyl2‐[aryl(tosylimino)methyl]acrylates from propiolate and N‐tosylimine has been developed. Deuterium‐labelling experiments show that the reaction mechanism involves several hydrogen‐transfer processes, which are not the turnover‐limiting step and strongly rely on the nature of the reaction media. The stable phosphonium–enamine zwitterion, which was proven to play
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.