High-Speed Microwave-Promoted Hetero-Diels−Alder Reactions of 2(1<i>H</i>)-Pyrazinones in Ionic Liquid Doped Solvents
作者:Erik Van der Eycken、Prasad Appukkuttan、Wim De Borggraeve、Wim Dehaen、Doris Dallinger、C. Oliver Kappe
DOI:10.1021/jo0263216
日期:2002.11.1
hetero-Diels-Alder reactions in a series of functionalized 2(1H)-pyrazinones were investigated under controlledmicrowave irradiation. The cycloaddition reactions were efficiently performed in sealed tubes, utilizing either a combination of 1,2-dichloroethane and a thermally stable ionicliquid, or 1,2-dichlorobenzene as reaction medium. In all cases, a significant rate-enhancement usingmicrowave flash heating
The title compounds were obtained from reaction of variously substituted 2(1H)pyrazinones with acetylenic derivatives. Experimental evidence points out to a two step mechanism : a DielsAlder cycloaddition followed by immediate decomposition of the adducts into the title products via two competitive retro DielsAlderreactions. The product distribution, which is shown to be highly dependent on the
acetylenic derivatives to give specifically substituted pyridones or pyridines. The observed selectivity can be explained in terms of HO-LU interactions for the reagents and two competitive retro Diels-Alderreactions of the primary bicycloadducts. With cyanotosylate as dienophile no pyrimidone derivative but a new 2(1H)-pyrazinone is obtained.