Synthesis and chemical application s of ansa-type compounds

在间位或对位桥联的芳香族化合物称为ANSA化合物。这类化合物在化学和生物上都是有用的。例如，阿萨霉素及其类似物是强大的抗生素，而吡啶膦类冠醚是金属的良好宿主。我们研究了一种新的ANSA类化合物的合成方法及其在分子识别化学中的应用。以前，我们发现1，3-二恶英-4-酮类化合物最容易通过热骨架生成。基于这一发现，我们研究了双酰基乙烯酮的生成及其分子内的环化反应，合成了ANSA类化合物。这个项目非常成功。通过双酰基酮中间体的分子内环化反应，高效地合成了一系列3位和6位桥联的4-羟基-2-吡喃和2-吡啶类化合物。这些ANSA类化合物具有平面手性，是手性伯胺的优良拆分剂。将得到的对映体纯胺首次应用于手性咪唑卡宾的合成，证明该催化剂对手性醇具有良好的动力学拆分性能。以桥联的4-羟基-2-吡喃为原料，通过环化反应合成了吡啶型12-冠-4，并研究了金属催化的开环歧化反应合成桥联吡喃，尤其是中、大环含环吡喃的合成。结果表明，与双酰基酮的分子内环加成反应相比，闭环歧化反应得到的桥联吡喃的产率要低得多。

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).