Isomerization ruthenium—carbene complexes

It has been revealed that the ruthenium carbene complex 6 can promote not only the olefin metathesis but also hydrogenation and isomerization. Louie et al. reported that the one-pot tandem ring-closing... 

Although numerous examples of successful RCM reactions have been demonstrated, a few limitations and/or side-reactions have been uncovered. Some cases where the RCM reaction proceeds with complications are depicted in Scheme 18. Sometimes RCM reactions are competitive with alkene isomerization. For example, the unexpected formation of 162 from precursor 160 was attributed to alkene isomerization (affording 161), followed by RCM to afford the ring-contracted compound 162. Later investigators went on to exploit this observation for the synthesis of cyclic enol ethers. Treatment of the allyl ether 164 with a ruthenium carbene complex catalyst affords the RCM... 

Cyclic allyl ethers generated by RCM can be isomerized into 2,3-dihydropyrans by a ruthenium complex and eventually by conditioning ruthenium carbene complex precursors [39]. This combination of sequentially Ru-catalyzed ring... 

The same reaction (RCM) was used as the key step for the formation of a family of potent herbicidal 10-membered lactones. An important aspect from the preparative point of view is the control of stereochemical outcome of the RCM by the choice of catalyst. Thus, the use of the ruthenium indenylidene complex IX always leads to the corresponding ( )-alkenes, whereas the second generation of Grubbs catalyst bearing a N-heterocyclic carbene ligand affords the isomeric (Z)-olefin with good selectivity (Scheme 8.19) [64]. 

Recently, we found that Af-allyl-o-vinylaniline 44 gave 1,2-dihydroquinoline 45 by normal RCM and developed silyl enol ether-ene metathesis for the novel synthesis of 4-siloxy-l,2-dihydroquinoline and demonstrated a convenient entry to quinolines and 1,2,3,4-tetrahydroquinoline [13], We also have found a novel selective isomerization of terminal olefin to give the corresponding enamide 46 using ruthenium carbene catalyst [Ru] and silyl enol ether [14], which represented a new synthetic route to a series of substituted indoles 47 [12], We also succeeded an unambiguous characterization of ruthenium hydride complex [RuH] with A -heterocyclic carbene... 

Another synthetically useful isomerization that can be combined with a metathesis event in a domino transformation is a metallotropic [l,3]-shift of a transient ruthenium aUdnyl carbene complex [33]. Treatment of the polyunsaturated substrate 162 with Grubbs catalyst 2 afforded the oligoenyne 163 in 86% yield... 

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