Diels-Alder reactions of 2-[(trialkylsilyl)oxy]pyrylium cations of 2H-pyran-2-one and 2H-1-benzopyran-2-one derivatives
作者:Katsuo Ohkata、Yong Gyun Lee、Yukinori Utsumi、Kenji Ishimaru、Kinya Akiba
DOI:10.1021/jo00017a014
日期:1991.8
The reactions of 6-methyl-2H-pyran-2-one and 2H-1-benzopyran-2-one with the 2-(trialkylsilyl)oxy dienes 6a-d in the presence of tert-butyldimethylsilyl triflate gave the [4 + 2] cycloadducts 7a-c and 8a-d regio- and stereoselectively in moderate yields. The ring junction in the cycloadducts is cis. The stereochemistry of 8a-d is discussed in terms of the H-1 NMR spectra of the compounds. Similar reactions of 3-(ethoxycarbonyl)-2-pyrones and 3-(alkoxycarbonyl)coumarins with the 2-(trialkylsilyl)oxy dienes 6a-e gave the cycloadducts 14-18 in satisfactory yields. Dehydrogenation of 7c, 8b, and 8c with DDQ in refluxing toluene afforded 23-25, respectively.