Department of Chemistry, National Tsing-Hua University, Hsinchu, Taiwan, ROC.
Chemistry. 2010 May 17;16(19):5803-11. doi: 10.1002/chem.201000009.
Treatment of 2-epoxy-1-alkynylbenzenes with electron-rich alkenes and a [AuCl(PR(3))]/AgX catalyst in CH(2)Cl(2) led to the formation of 2-alkenyl-1-(2,3-dihydrofuran-4-yl)benzenes. This transformation comprises of a gold-catalyzed redox reaction to form a gold alpha-carbonylcarbenoid initially, which then reacts in situ with an alkene in a [3+2] cycloaddition. A range of alkenes are amenable to this tandem reaction, amongst them alpha-substituted styrenes, enol ethers, and 2,3-dimethylbutadienes. Deuterium-labeling experiments suggest a stepwise mechanism for the alpha-carbonylcarbenoid/alkene [3+2] cycloaddition. The resulting 2,3-dihydrofuran products allow access to diverse oxacyclic compounds through a stereoselective ene-oxonium reaction initiated by treatment with HOTf (1 mol %; Tf=trifluoromethanesulfonyl). A stepwise pathway is proposed for this reaction. The feasibility for direct transformation of 2-alkenyl-1-alkynylbenzenes into the desired 2,3-dihydrofuran products through initial m-chloroperbenzoic acid oxidation, followed by the addition of gold catalyst and alkene, has also been demonstrated.
用富电子烯烃和 [AuCl(PR(3))]/AgX 催化剂在 CH(2)Cl(2)中处理 2-环氧-1-炔基苯，生成 2-烯基-1-(2,3-二氢呋喃-4-基)苯。该转化包括金催化的氧化还原反应，最初形成金α-羰基金属卡宾，然后与烯烃在 [3+2]环加成中就地反应。一系列烯烃都适用于此串联反应，包括α-取代的苯乙烯、烯醇醚和 2,3-二甲基丁二烯。氘标记实验表明，α-羰基金属卡宾/烯烃 [3+2]环加成具有分步机制。所得的 2,3-二氢呋喃产物可通过用 HOTf（1mol%；Tf=三氟甲磺酸）引发的立体选择性烯-氧翁反应，得到各种氧杂环化合物。提出了该反应的分步途径。通过直接转化 2-烯基-1-炔基苯为所需的 2,3-二氢呋喃产物的可行性也通过初始 m-氯过苯甲酸氧化，然后加入金催化剂和烯烃来证明。
