Rhenium(I)-Catalyzed Intramolecular Geminal Carbofunctionalization of Alkynes: Tandem Cyclization of ω-Acetylenic Dienol Silyl Ethers.-猫眼课题宝

DOI：

10.1002/chin.200521081

发表时间：

2005-05

期刊：

ChemInform

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

H. Kusama;H. Yamabe;Yuji Onizawa;Takahiko Hoshino;N. Iwasawa

基于以上考虑，我们设计了如图2所示的系统。因此，用适当的金属试剂处理炔属二烯醇甲硅烷基醚 1 应通过烯醇甲硅烷基醚的 5-内亲核环化至亲电活化的 h2-炔配合物 A 得到两性离子中间体 B。然后，产生的烯基金属部分应在金属中心的 b-位置对 a，b-不饱和硅氧鎓部分进行分子内攻击，产生双环不稳定最后，不稳定的卡宾配合物部分将经历典型的卡宾反应，例如1, 2-氢迁移，得到具有活性金属物质再生的产物。 [6]我们首先研究了在分子筛存在下，在甲苯中光照射下，w-乙炔二烯醇甲硅烷基醚 1a 与 10 mol% 的 [W (CO) 6] 的反应（4）（表 1）。尽管以前没有研究过烯醇甲硅烷基醚与内部炔烃部分的钨催化环化反应[7]，但反应按预期进行，并且以高收率获得了所需的双环烯醇甲硅烷基醚2a，为非对映体混合物，并伴有少量三环化合物3a。 [8]由于发现孪生碳官能化按预期进行，我们进一步研究了使用其他过渡金属配合物的可能性。 PtCl2 [2b, c, e, f]（67% 产率）和 AuBr3[2d, e]（79% 产率）对该转化也表现出中等的催化活性，此外 [ReCl (CO) 5] 被发现具有极高的活性。即使使用 0.5 mol% 的 [ReCl (CO) 5]，反应仍可进行，通过在甲苯中光照射下进行反应，以 86:14 的比例生成环化产物 2a 和 3a，产率达 92%。 [9, 10] 三环化合物 3a 的形成明确暗示了中间体卡宾配合物 C 的存在，其中卡宾部分插入到邻近的卡宾部分中。苄基 CÀH 键。一旦我们确定 [ReCl (CO) 5] 非常有效地催化孪生碳官能化反应，就检查了几种底物的反应（表 2）。在位 (R2) 处带有甲基、伯烷基或仲烷基以及苯基的三取代二烯 (1b–e)[11] 环化，以高产率提供相应的双环烯醇甲硅烷基醚（表 2，条目 1–4）。甚至四取代二烯（1f，1g）[11]的反应也继续进行，以高产率提供相应的取代双环烯醇甲硅烷基醚。在大多数情况下，[ReCl (CO) 5] 催化反应的结果优于 [W (CO) 5 (L)] 催化的反应。 [12]特别是，b位无取代基（R2=H）的二烯基甲硅烷基醚1h和1i的铼催化反应以中等至高产率提供了所需的双环烯醇甲硅烷基醚。然而，即使使用化学计量的[W (CO) 5 (L)] 1i，相应的钨催化反应也以非常低的产率（17％）进行。此外，具有末端炔烃部分 1j [11] 的底物也可用于该反应（表 2，条目 9）。低价铼配合物在催化合成反应中的使用，特别是C-C键形成反应，是相当有限的。 [13]这

On the basis of the above considerations we designed the system shown in Scheme2. Thus, treatment of acetylenic dienol silyl ethers 1 with an appropriate metallic reagent should give zwitterionic intermediates B by 5-endo nucleophilic cyclization of the enol silyl ether to the electrophilically activated h2-alkyne complexes A. The alkenyl metallic moiety produced should then undergo an intramolecular attack at the b-position of the metal center to the a, b-unsaturated silyloxonium moiety to generate bicyclic unstable carbene complexes C. Finally, the destabilized carbene complex moiety would undergo a typical carbene reaction, such as 1, 2-hydrogen migration, to give the products with regeneration of the reactive metallic species.[6] We first examined the reaction of w-acetylenic dienol silyl ether 1a with 10 mol% of [W (CO) 6] under photoirradiation in toluene in the presence of molecular sieves (4)(Table 1). Although the tungsten-catalyzed cyclization reaction of enol silyl ethers with an internal alkyne moiety has not been examined before,[7] the reaction proceeded as expected and the desired bicyclic enol silyl ether 2a was obtained in high yield as a mixture of diastereomers accompanied by a small amount of tricyclic compound 3a.[8] Since geminal carbofunctionalization was found to proceed as expected, we further examined the possibility of using other transition-metal complexes. PtCl2 [2b, c, e, f](67% yield) and AuBr3[2d, e](79% yield) also showed moderate catalytic activity towards this transformation, and furthermore [ReCl (CO) 5] was found to have an extremely high activity. The reaction proceeded even with 0.5 mol% of [ReCl (CO) 5] to give the cyclized products 2a and 3a in 92% yield in a ratio of 86: 14 by carrying out the reaction in toluene under photoirradiation.[9, 10] Formation of the tricyclic compound 3a explicitly implicates the presence of the intermediate carbene complex C, in which the carbene moiety inserts into the neighboring benzylic CÀH bond. Once we established that [ReCl (CO) 5] catalyzed the geminal carbofunctionalization reaction very efficiently, the reaction of several substrates was examined (Table 2). The trisubstituted dienes (1b–e)[11] with a methyl, primary, or secondary alkyl group as well as a phenyl group at the bposition (R2) were cyclized to afford the corresponding bicyclic enol silyl ethers in high yield (Table 2, entries 1–4). Even the reaction of the tetrasubstituted dienes (1 f, 1g)[11] proceeded to afford the corresponding substituted bicyclic enol silyl ethers in high yield. The [ReCl (CO) 5]-catalyzed reaction gave superior results in most cases relative to that catalyzed by [W (CO) 5 (L)].[12] In particular, the rheniumcatalyzed reaction of dienyl silyl ethers 1h and 1i with no substituent at the b-position (R2= H) afforded the desired bicyclic enol silyl ethers in moderate to high yields. However, the corresponding tungsten-catalyzed reaction proceeded in very low yield (17%) even with a stoichiometric amount of [W (CO) 5 (L)] for 1i. In addition, a substrate possessing a terminal alkyne moiety 1j [11] could also be employed for this reaction (Table 2, entry 9). The use of lowvalent rhenium complexes in catalytic synthetic reactions, in particular for CÀC bond forming reactions, is quite limited.[13] The

Rhenium(I)-Catalyzed Intramolecular Geminal Carbofunctionalization of Alkynes: Tandem Cyclization of ω-Acetylenic Dienol Silyl Ethers.

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