標題: Stereoselectivity of the Diels-Alder reaction of (E)gamma-Oxo-alpha,beta-unsaturated thioesters with cyclopentadiene
作者: Tsai, SH
Chung, WS
Wu, HJ
應用化學系
Department of Applied Chemistry
公開日期: 1-Jun-1996
摘要: The stereoselectivity of the Diels-Alder reaction of (E)-gamma-oxo-alpha,beta-unsaturated thioesters 3a-3d with cyclopentadiene is greatly enhanced in the presence of Lewis acids favoring the endo acyl isomers 4a-4d. In the absence of Lewis acid, Diels-Alder reaction of 3a-3d with cyclopentadiene at 25 degrees C gave two adducts 4a-4d and 5a-5d in a ratio of 1:1 respectively. In the presence of Lewis acids, Diels-Alder reaction of 3a-3d with cyclopentadiene gave 4a-4d and 5a-5d in ratios of 75 similar to 94:25 similar to 6 respectively. The stereoelectivity was enhanced to ratios of 95 similar to 98:5 similar to 2 with lowering the reaction temperature. The stereochemistry of the cycloadducts 4 and 5 was confirmed by iodocyclization. Reaction of the endo-thioester 5c with I-2 in aqueous THF at 0 degrees C gave the novel methylthio group rearranged product 6c in 80% yield, the first example of iodolactonization of endo-thioesters. Reaction of the endo-acyl isomer 4b with I-2 under the same reaction conditions gave an isomeric mixture of 7b and 8b in 1:2 ratio. The stereochemistry of the thioester group in 8b was proved by X-ray single-crystal analysis. The solvent effect on the endo selectivity of (Z)-gamma-oxo-alpha,beta-unsaturated thioester 2b was also examined.
URI: http://hdl.handle.net/11536/1271
ISSN: 0009-4536
期刊: JOURNAL OF THE CHINESE CHEMICAL SOCIETY
Volume: 43
Issue: 3
起始頁: 281
結束頁: 288
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