Synthese von mittleren Ringen durch Ringschluss-Metathese-Reaktion

Abstract

Konformative Einschränkung ist der Schlüssel für die effiziente Synthese mittlerer Ringe durch Ringschluss‐Olefin‐Metathese (RCM). Nachdem sich die RCM‐Reaktion schon bei der Synthese größerer Makrolide wie Epothilon bewährt hat, wird sie in jüngerer Zeit verstärkt zum Aufbau acht‐ bis zehngliedriger Carbo‐ und Heterocyclen genutzt. Im gezeigten Beispiel sorgt der anellierte Cyclopentanring für die konformative Einschränkung und gewährleistet so die Cyclisierung.

Why is RCM Favoured Over Dimerisation? Predicting and Estimating Thermodynamic Effective Molarities by Solution Experiments and Electronic Structure Calculations

“…Non-annelative closure of eight-membered rings is usually an unfavourable reaction [25] and reactions that form Z-cyclooctenes usually require either appropriate vicinal ring substitution, often referred to as "gearing", [26] or fusion to other ring systems. [27] We could also clearly see cyclohexene 3 b (d H (CD 2 Cl 2 ) = 5.69 ppm) and cycloheptene 3 c (d H (CD 2 Cl 2 ) = 2.15 ppm and 1.64 ppm) by 1 H NMR in the metathesis of 1 d. The presence of products derived from one and two successive isomerisation steps followed by cyclisation demonstrates that the cyclisation of the propagating carbene derived from 1 d is particularly slow. Table 2 shows the highest [1] 0 concentrations at which clean RCM was achievable.…”

Polymer-Supported Well-Defined Metathesis Catalysts

“…Since its discovery, olefin metathesis has experienced dramatic developments and is nowadays considered to be one of the most important C−C bond-forming reactions, − allowing for the synthesis of both well-defined, functional (block co-) polymers and complex organic molecules including medium-sized and large ring structures. , The fact that these reactions can be carried out in an enantioselective way − widened the range of applications from commodity chemicals to the synthesis of optically active compounds relevant to pharmaceutical chemistry.…”