- 作者: 蔡世華 ; 鍾文聖 ; 吳獻仁
- 作者服務機構: 交通大學應用化學系
- 中文摘要: 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.degree.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 75-94:25- 6 respectively. The stereoselectivity was enhanced to ratios of 95-98:5-2 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/ sub 2/ in aqueous THF at 0.degree.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/sub 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.
- 英文摘要: --
- 中文關鍵字: Stereoselectivity; Diels-Alder Reaction; Thioester; Cyclopentadiene
- 英文關鍵字: 立體選擇性;Diels-Alder反應;硫酯;環戊雙烯