Sparks Steven M, Chen Chi-Li, Martin Stephen F
Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University Station A5300 Austin, TX 78712-0165.
Tetrahedron. 2007 Aug 27;63(35):8619-8635. doi: 10.1016/j.tet.2007.04.031.
We have exploited tandem intramolecular benzyne-furan cycloadditions employing three different benzyne precursors to generate substituted bisoxabenzonorbornadienes in a single operation. The regiochemical outcomes in these Diels-Alder reactions were effectively controlled by using disposable silicon tethers to link the reacting benzynes and furan moieties. Two different methods for converting the intermediate bisoxabenzonorbornadienes to substituted anthrarufins were developed. The first tactic entails the initial cleavage of the silicon tethers followed by regioselective ring opening of the oxabicycloheptadienes and oxidation of the central ring giving the target anthrarufin, whereas the second features the regioselective ring opening of the oxabicycloheptadienes followed by protiodesilylation and oxidation. When the starting furans bear carbohydrate substitutents, this new methodology enables the rapid assembly of the glycosyl-substituted aromatic cores of complex C-aryl glycoside antibiotics from simple starting materials. The utility of this novel approach to anthrarufins and C-aryl glycosides is exemplified in a triply convergent synthesis of vineomycinone B(2) methyl ester.
我们利用串联分子内苯炔-呋喃环加成反应，采用三种不同的苯炔前体，通过一次操作生成取代的双氧杂苯并降冰片二烯。在这些狄尔斯-阿尔德反应中，区域化学结果通过使用一次性硅连接基将反应性苯炔和呋喃部分连接起来而得到有效控制。我们开发了两种将中间体双氧杂苯并降冰片二烯转化为取代蒽鲁芬的不同方法。第一种策略是先切断硅连接基，然后对氧杂双环庚二烯进行区域选择性开环，并氧化中心环，从而得到目标蒽鲁芬；而第二种方法的特点是先对氧杂双环庚二烯进行区域选择性开环，然后进行脱硅质子化和氧化。当起始呋喃带有碳水化合物取代基时，这种新方法能够从简单的起始原料快速组装复杂的C-芳基糖苷抗生素的糖基取代芳环核心。这种合成蒽鲁芬和C-芳基糖苷的新方法的实用性在维诺霉素酮B(2)甲酯的三重汇聚合成中得到了体现。
