Ringschlussmetathese: ein Schlüssel zur Arensynthese

Abstract

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.

Enyne Metathesis–Oxidation Sequence for the Synthesis of 2‐Phosphono Pyrroles: Proof of the “Yne‐then‐Ene” Pathway

“…[19] The synthesis of aromatic compounds by RCM has only recently appeared in the literature, [20] but it is emerging as an important area and has very recently been reviewed by Donohoe and co-workers. [21] We also offer evidence pointing to the yne-then-ene pathway in this particular case. The evidence is threefold and is based on 1) the formation of certain end and byproducts, 2) the difference in reactivity of different substrates, and 3) spectroscopic data.…”

Ru‐ and Pd‐Catalysed Synthesis of 2‐Arylfurans by One‐Flask Heck Arylation/Oxidation

“…Assisted tandem [26] RCM/aromatization sequences, [27,28] characterized by the use of a single Ru precatalyst that undergoes an organometallic conversion to a dehydrogenation catalyst in situ, are scarce. [29][30][31] In most cases the heteroaromatic product is obtained in minor quantities as a side product, or the reaction is not general and difficult to reproduce.…”

Olefin‐Metathesis‐Based Synthesis of Furans by an RCM/Deprotonation/Phosphorylation Sequence and Their Diels–Alder Reactions

“…[a] Conversion of 5 into the corresponding furanyl phosphate 3 was quantitative based on 1 Scheme 4. Diels-Alder reaction of 2-methoxyfuran and thermal rearrangement to a phenol.…”

“…[1,2] Reactions previously described in the literature can be classified as assisted tandem catalytic [3] RCM/aromatization sequences, [4][5][6] one-flask sequences comprising an Ru-catalysed RCM step followed by an oxidation [7][8][9][10] or elimination reaction, [11][12][13] and twostep procedures involving isolation of the RCM product, which is then converted into an aromatic compound. [14,15] Due to the significance of substituted furans as synthetic intermediates and as structural elements in various drugs and drug candidates, we started to explore metathesis-based routes for the synthesis of these aromatic heterocycles.…”