以金屬催化合成四氫喃衍生物
Abstract
四氫喃的結構是許多天然物的特徵之ㄧ，因此有許多有機化學家致力於研究如何製備異核環形的分子。在此我們利用CeCl3．7H2O和NaI成功地催化帶有一級或三級醇之非環形雙烯化合物進行分子內環化反應，順利得到一系列2號及5號碳上帶有取代基的四氫喃衍生物。
另一方面，我們使用鈀金屬催化γ位置帶有羥基之非環形雙烯化合物與芳香烴溴化物進行反應，可得到1,2加成的環化產物。而以鋅銅試劑製備所得的帶酯官能基之環已二烯三羰鐵錯合物，經氧化劑去錯合和與親核試劑反應之後，帶醇基之環己二烯分子在同樣的條件之下亦可進行環化，並且經由環化過程所建立的新的立體中心，其碳上的氫都是同向的。
Cesium (III) chloride heptahydrate catalyzed intramolecular cyclization of acyclic-hydroxydienes was studied. Sodium iodide (0.1 eq) was used as the co-catalyst. The reaction was carried out in refluxing acetonitrile under nitrogen to afford C-2 and C-5 disubstituted tetrahydrofurans. Palladium-catalyzed reaction of aryl bromides with -hydroxy 1,3-dienes led to an 1,4- or 1,2-oxyarylation to the conjugated dienes. With cyclic -hydroxy 1,3-dienes, the reaction proceeded via a (-allyl)palladium intermediate, which was presumably formed by insertion of the olefin into the Pd-O bond of a postulated Pd(Ar)(OR)-olefin complex. Rearrangement of the (-allyl)palladium intermediate followed by C-C bond forming reductive elimination led to an overall 1,4-oxyarylation. While reaction of aryl bromides with acyclic -hydroxy 1,3-dienes gave 1,2-oxyarylation products under the same reaction conditions. The1,2-oxyarylation reaction presumably proceeded via insertion of the olefin into the Pd-C bond of the postulated Pd(Ar)(OR)-olefin complex followed by C-O bond forming reductive elimination.
Cesium (III) chloride heptahydrate catalyzed intramolecular cyclization of acyclic-hydroxydienes was studied. Sodium iodide (0.1 eq) was used as the co-catalyst. The reaction was carried out in refluxing acetonitrile under nitrogen to afford C-2 and C-5 disubstituted tetrahydrofurans. Palladium-catalyzed reaction of aryl bromides with -hydroxy 1,3-dienes led to an 1,4- or 1,2-oxyarylation to the conjugated dienes. With cyclic -hydroxy 1,3-dienes, the reaction proceeded via a (-allyl)palladium intermediate, which was presumably formed by insertion of the olefin into the Pd-O bond of a postulated Pd(Ar)(OR)-olefin complex. Rearrangement of the (-allyl)palladium intermediate followed by C-C bond forming reductive elimination led to an overall 1,4-oxyarylation. While reaction of aryl bromides with acyclic -hydroxy 1,3-dienes gave 1,2-oxyarylation products under the same reaction conditions. The1,2-oxyarylation reaction presumably proceeded via insertion of the olefin into the Pd-C bond of the postulated Pd(Ar)(OR)-olefin complex followed by C-O bond forming reductive elimination.
Description
Keywords
鈀, 鈰, 四氫喃