Synthesis and chemical application s of ansa-type compounds

桥连在Meta位或帕拉的芳族化合物称为柄型化合物。这类化合物在化学和生物学上都是有用的。例如，安莎霉素及其类似物是强有力的抗生素，吡啶并噻吩型冠醚是金属的优良宿主。我们研究了一种合成柄型化合物的新方法及其在分子识别化学中的应用，发现1，3-二氧杂环己烯-4-酮衍生物经热裂解可以方便地合成酰基烯酮，并通过对它们的结构进行了表征。在此基础上，我们研究了双（酰基烯酮）的生成及其分子内环化生成柄型化合物。这个项目非常成功。以双酰基烯酮为中间体，通过分子内环化反应，高效地合成了一系列3位和6位桥联的4-羟基-2-吡喃酮和2-吡啶。这些柄型化合物具有平面手性，是手性伯胺的优良拆分试剂。由此得到的对映体纯的胺被应用于手性咪唑卡宾的首次合成，该手性咪唑卡宾被证明是用于手性醇的动力学拆分的有用催化剂。通过桥连4-羟基-2-吡喃酮的环化反应合成了吡啶并吡喃型12-冠-4，并研究了金属催化的关环复分解反应合成桥连吡喃酮，其中包括环番在内的中、大环化合物的合成受到了广泛的关注。结果表明，通过闭环复分解得到的桥联吡喃酮的产率远低于通过双酰基烯酮的分子内环加成得到的产物。

Aromatic compounds bridged at the meta or para positions are referred to ansa compounds. This class of compounds is chemically and biologically useful. For example, ansamycin and its analogs are powerful antibiotics and pyridinophane-type crown ethers serve as excellent host for metals. However, these ansa-type compounds are not readily accessible due to their much strain by the strained bridged structure.We have studied a new method for synthesizing ansa-type compounds and their use in molecular recognition chemistry.Previously, we found that acylketenes can be generated most conveniently by thermal fragnentation of 1,3-dioxin-4-one derivatives. Based on this finding, we studied generation of bis(acylketene) and their intramolecular cyclization to produce ansa-type compounds. This project was very much successful. A series of 4-hydroxy-2-pyrones and 2-pyridines bridged at the 3- and 6-positions was synthesized by the intramolecular cyclization of bis(acylketene) intermediate highly effciently. These ansa-type compounds have planar chirality and served as excellent resolution reagent for chiral primary amines. Enantiomerically pure amines thus obtained were applied to the first synthesis of chiral imidazolium carbenes that proved to be useful catalyst for kinetic resolution of chiral alcohols. Pyridinophane-type 12-crown-4 was synthesized by ring transformation of the bridged 4-hydroxy-2-pyrones.We have also studied synthesis of bridged pyrones by metal-catalyzed ring-closing metathesis to that increasing attention has been diected toward the synthesis of medium and large rings inclucing cyclophanes. The results indicated that ring-closing metathesis afford the bridged pyrones in much lower yields than that by intramolecular cycloaddition of bis (acylketene).