Ruthenium ring-closing metathesis

Negishi E, Tan Z (2005) Diastereoselective, Enantioselective, and Regioselective Carbo-alumination Reactions Catalyzed by Zirconocene Derivatives. 8 139-176 Netherton M, Fu GC (2005)Pa]ladium-catalyzed Cross-Coupling Reactions of Unactivated Alkyl Electrophiles with Organometallic Compounds. 14 85-108 Nicolaou KC, King NP, He Y (1998) Ring-Closing Metathesis in the Synthesis of EpothUones and Polyether Natmal Products. 1 73-104 Nishiyama H (2004) Cyclopropanation with Ruthenium Catalysts. 11 81-92 Noels A, Demonceau A, Delaude L (2004) Ruthenium Promoted Catalysed Radical Processes toward Fine Chemistry. 11 155-171... 

Ring-closing metathesis has been successfully used in the synthesis of [3.5.0], [4.5.0], and [5.5.0] ring systems <2001TL8231>. The ruthenium complex 160 was employed on both symmetrical and unsymmetrical substrates with equal success, as outlined in Equation (15). Compounds 161-164 were synthesized in this fashion. 

The synthesis of the /V-protected 7-methylazepine derivative 34 was achieved in 89% yield by a ring-closing metathesis reaction on 33 mediated by Grubbs I ruthenium catalyst. This azepine was an important precursor for the preparation, via epoxidation of the double bond, of a number of 7-methylazepanone derivatives for evaluation as cathepsin K inhibitors <06JMC1597>. 

Ring-closing metathesis on the dienes 116 and 117 with Grubbs ruthenium catalyst II 18 afforded the 7-membered ring sulfones 118 and 119 respectively. The diene precursor 116 was accessed from reaction of the sulfonyl chloride 115 with 3-buten-l-ol 114 <06T9017>. 

Representatives of the bridged sulfone system 70 have been subjected to ruthenium catalysed ring-closing metathesis reactions (Grubbs catalyst) and shown to afford, in low yields, a few selected cyclic dimers and trimers, of all the possibilities available. The diastereoselectivities observed were rationalised in terms of kinetic control involved with internal ruthenium/sulfonyl oxygen coordination . 

The ruthenium-catalyzed isomerization of aryl allyl ethers or amines followed by ring-closing metathesis with ruthenium catalyst 1 furnishes fused benzo-heterocycles in good yield (Scheme 40).66 67... 

Keywords Ruthenium-carbenes, Ruthenium-allenylidenes, Ring closing metathesis, Natural product synthesis, Fine chemicals. 

The ruthenium catalyst system, 14, shown in Fig. 3, also carries out ADMET condensation chemistry, albeit with higher concentrations being required to achieve reasonable reaction rates [32]. The possibility of intramolecular compl-exation with this catalyst influences the polymerization reaction, but nonetheless, ruthenium catalysis has proved to be a valuable contributor to overall condensation metathesis chemistry. Equally significant, these catalysts are tolerant to the presence of alcohol functionality [33] and are relatively easy to synthesize. For these reasons, ruthenium catalysis continues to be important in both ADMET and ring closing metathesis chemistry. 

Nicolaou KC, King NP, He Y (1998) Ring-Closing Metathesis in the Synthesis of Epothilones and Polyether Natimal Products. 1 73-104 Nishiyama H (2004) Cyclopropanation with Ruthenium Catalysts. 11 81-92 Nobis M, see Hugl H (2008) 23 1-17... 

Scheme 8.17 Ring closing metathesis of dienes with ruthenium-indenylidenes IX and XXV.

Ring-closing metathesis, which has proved to be a popular route to the marine toxins, has found a further application as the key step in the synthesis of the pheromone (-)- and ( )-frontalin <99TL1425>. The precursor in this reaction is a mixture of the syn- and anri-isomers 39. Ring closure in the presence of a ruthenium benzylidene catalyst occurs within minutes at room temperature when only the syn-isomer cyclises to 40. The unreacted anri-isomer can be re-equilibrated for a further cyclisation. 

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