The use of metathesis, especially in the context of ring-closing metathesis (RCM) to form five- and six-membered rings, is widespread in organic chemistry today. However, there are surprisingly few examples of the reaction being used to form aromatic compounds. The central place of aromatic compounds in both medicinal chemistry and natural products synthesis, coupled with the efficiency and functional group tolerance of RCM catalysts, means that there is now an interesting opportunity to use RCM for the synthesis of arenes. Although the formation of an aromatic compound was viewed in many early examples as an undesirable degradation product, several rationally designed methods towards the preparation of aromatic compounds by RCM have recently been developed.
The ring closing metathesis (RCM) reaction can be used to prepare substituted furans and pyrroles. By utilising a Pdcatalysed coupling reaction with methoxyallene, allylic alcohols and sulfonamides can be converted into substrates that are ideal precursors to ring closing metathesis. After the RCM reaction is complete, the addition of acid promotes an elimination of methanol to form the fully aromatised system.
Die Anwendung der Metathese, besonders der Ringschlussmetathese (RCM) zur Bildung von Fünf‐ und Sechsringen, ist heute in der organischen Chemie weit verbreitet; dennoch gibt es überraschend wenige Beispiele für ihre Anwendung zur Synthese aromatischer Verbindungen. Deren Bedeutung in der medizinischen Chemie und der Naturstoffsynthese, verbunden mit der Wirksamkeit von RCM‐Katalysatoren und ihrer Toleranz gegenüber funktionellen Gruppen, gibt Anlass, die Anwendung der RCM in der Arensynthese zu untersuchen. Die Synthese von heterocyclischen und carbocyclischen Arenen unter Verwendung der RCM wird in einigen Publikationen als Schlüsselschritt beschrieben. Galt das gebildete Aren in vielen frühen Beispielen noch als unerwünschtes Abbauprodukt, so wurden in letzter Zeit gezielt Methoden zur Arensynthese über RCM entwickelt.
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