Development of New Methods for Constructing Medium Sized Carbocycles by Using Acetylene Dicobalt Complexes

(1)[5+2]环加成反应的新进展为了探讨具有乙炔二钴配合物和烯醇硅醚段的五碳单元的[5+2]环加成反应的范围和局限性，研究了与各种富电子烯烃和芳香族化合物的反应。虽然芳香化合物包括茴香醇和苯胺衍生物没有很好的结果，但发现与硅氧allene衍生物的反应可以得到所需的七元环加合物，收率很高。(2)高阶环加成反应的发展一个新的六碳单元是传统五碳单元的同源物，与烯醇三异丙基硅醚进行了光滑的[6+2]环加成反应，得到了具有高立体选择性的八元乙炔二钴配合物。用烯丙基硅基醚代替烯醇硅基醚，通过[6+3]环加成反应形成九元环。得到的环乙炔二钴配合物经CAN处理后转化为相应的旋风炔衍生物。另一方面，六碳单元与呋喃的反应通过[6+4]环加成反应形成具有醚桥的十元碳环。(3)在天然产物合成中的应用在硅氧基烯衍生物的[5+2]环加成反应构建氢偶氮烯骨架的新方法的基础上，完成了呋喃醚B的全合成。

(1)New aspects of [5+2] cycloaddition reactionsIn order to explore the scope and limitations of the [5+2] cycloaddition reaction using the five-carbon unit having an acetylene dicobalt complex moiety and an enol silyl ether moiety, the reactions with various electron rich olefins as well as aromatic compounds were examined. Although aromatic compounds including anisols and aniline derivatives gave no good results, the reaction with a siloxyallene derivative was found to give the desired seven-membered cycloadduct in good yield.(2)Development of the higher-order cycloaddition reactionsA new six-carbon unit, a homologue of the conventional five-carbon unit, underwent a smooth [6+2] cycloaddition reaction with an enol triisopropylsilyl ether giving rise to an eight-membered acetylene dicobalt complex with high stereoselectivity. Use of an allyl silyl ether instead of an enol silyl ether resulted in formation of a nine-membered ring via a [6+3] cycloaddition reaction. The resulting cyclic acetylene dicobalt complex was converted into the corresponding cyclononyne derivative by treating with CAN. On the other hand, the reaction of the six-carbon unit and furan afforded a ten-membered carbocycle having an ether bridge through a [6+4] cycloaddition reaction.(3)Application to the synthesis of natural productsTotal synthesis of furanether B was accomplished on the basis of a new method for constructing a hydroazulene skeleton through the [5+2] cycloaddition reaction of a siloxy allene derivative.