Ruthenium isomerization catalyst

Ruthenium-carbenoid catalyst 1 promotes the isomerization of /3,7-unsaturated amines to the corresponding enamines (Equation (4)).21 This reaction is useful in the deprotection of amines. 

Depending on the substrate, the enallenes 213 react with a ruthenium-hydrido catalyst to give either the initial product the methylenecyclopentanes 214 with a 1,4-diene substructure or to the conjugated vinylcyclopentenes 215. The latter are formed by a subsequent ruthenium-catalyzed isomerization of the initial cycization product 214 (Scheme 15.69) [136]. 

Ruthenium is commonly used with other platinum metals as a catalyst for oxidations, hydrogenations, isomerizations, and reforming reactions. The synergetic effect of mixing ruthenium with catalysts of platinum, palladium, and rhodium lias been found for the hydrogenations of aromatic and aliphatic nitro compounds, ketones, pyndine, and nitriles. 

The control of alkene geometry in RCM reactions has been an area of intense research and interest since the process was first developed. While a general solution to this challenge has not yet been developed, intriguing observations of E Z control in macrocyclizations continue to be reported. For example, in the course of their studies on the synthesis of herbarumin I and II, Fiirstner and co-workers reported the selective formation of either of the two isomeric alkene products 16 or 17 via RCM of diene 15 <02JA7061> (Scheme 8). The diene 15 was transformed into the -alkene 17 using the ruthenium indenylidene catalyst (Fiirstner Metathesis Catalyst FMC, <01MI4811>) while use of the MC2 led to clean formation of the Z-isomer 16. 

A tandem RCM-alkene isomerization sequence to form 5-, 6-, and 7-membered enol ethers was reported by Snapper and co-workers <02JA13390> (Scheme 36). In this process the RCM reaction is run under an atmosphere of 95 5 N2.TI2 to convert the intermediate ruthenium alkylidene into an olefin-isomerization catalyst. Note that alkene migration can convert isomeric metathesis products into the same 2,3-enol ether. A single example of the formation of a 6-membered tosyl enamide was reported in this manuscript. 

Comparison of this sequence with Fig. 33 shows clearly that the metals that are most active for olefin isomerization, rhodium (> 80°) and nickel, yield the least 1-butene in 1,3-butadiene hydrogenation the reverse is also true in that copper and iridium, being poor isomerization catalysts, give the most 1-butene. Platinum, ruthenium, and osmium occupy intermediate positions in the expected order. Furthermore, the activity of all metal catalysts for isomerization increases with increasing temperature and the yield of 1-butene from 1,3-butadiene decreases as the temperature is raised this agrees with expectation and helps to confirm the proposed mechanism. 

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... 

This method allows the quantification of the olefin isomerization that may occur in the course of ADMET polymerization using second generation ruthenium metathesis catalysts. 

Further, it was demonstrated that the addition of benzoquinone to the polymerization mixture prevents the olefin isomerization. Therefore, second generation ruthenium metathesis catalysts can be used for the preparation of well defined polymers via an ADMET technique causing little isomerization (32). 

Scheme 7.15 Calculated mechanisms for olefin Isomerization (a) hydride-transfer mechanism with a ruthenium hydride catalyst, adapted from Ref [65, 66] and (b) methylldene Insertion Into an allyllc C-H bond, adapted from Ref [63]. All energies are Gibbs free energies In kcal mor. ...

Sertchook H., Avnir D., Blum J., J06 F., Katho A., Schumann H., Weimann R., Wemik S. Sol-gel entrapped lipophilic and hydrophilic ruthenium-, rhodium- and iridrum-phosphine complexes as recyclable isomerization catalysts. J. Mol. Catal. A Chem. 1996 108 153-160 Shvo Y., Becker Y. Sol-gel glass with enantioselective catalytic activity. J. Chem. Soc., Chem. Commun. 1994 2719-2720... 

On the basis of the interesting results just discussed, the isomeric 5-substituted 1,2,3-triazoles 22 using a ruthenium-based catalyst were synthesized (Scheme 2.4) [38]. This new series of compounds (22, R = Ph) resulted in activity against human CAs IX (67.1 nM) and XII (9.5 nM) with Aj values in the nanomolar range but were inactive against CAs I (>10 pM) and CAs II (>10 pM). 

Another example is the hydrogenation of the homoallylic eompound 4-methyl-3-cyclohexenyl ethyl ether to a mixture of 4-methylcyclohexyl ethyl ether and methylcyclohexane. The extent of hydrogenolysis depends on both the isomerizing and the hydrogenolyzing tendencies of the catalysts. With unsupported metals in ethanol, the percent hydrogenolysis decreased in the order palladium (62.6%), rhodium (23 6%), platinum (7.1%), iridium (3.9%), ruthenium (3.0%) (S3). 

In the presence of copper and palladium catalysts, terminal alkynes 1222 react with trimethylsilyl azide and allyl methyl carbonate to provide 2,4-disubstituted 1,2,3-triazoles 1223 in moderate to good yield. Isomerization of the allyl substituent in the presence of a ruthenium catalyst gives 4-substituted 2-(l-propen-l-yl)-2//-l,2,3-triazoles 1224. 

Various ruthenium complexes catalyze the isomerization of allylic alcohols to saturated carbonyl compounds. Ru(acac)3 is an effective catalyst for the isomerization of a wide range of allylic alcohols (Scheme 12).35... 

High chemoselectivity is observed in this ruthenium-catalyzed isomerization of allylic alcohols. Simple primary and secondary alcohols and isolated double bonds are not affected by these catalysts. Furthermore, free hydroxy group is essential for this catalysis. The reaction of l-acetoxycyclododec-2-ene-4-ol furnished 4-acetoxycyclododecanone in high yield (Scheme 14).37... 

Isomerization of [(, )-3-alkoxy-l-propenyl]boronates to the corresponding 7-alkoxyallylboronates was catalyzed by ruthenium or iridium complexes.64 [IrH2(TFlF)2(PPh2Me)2]PF6 was the most efficient catalyst for selective preparation of (ftfy-alkoxyallylboronates (Scheme 37). 

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... 

Desymmetrization of cyclic allyl acetals such as 2-substituted 4,7-hydrodioxepins or 5-methylene-1,3-dioxanes was investigated using ruthenium or nickel catalysts. The isomerization of the dioxanes was accomplished using Ru2Cl4(DIOP)/LiBHEt3 in high yield with up to 38% ee (Equation (22)).81... 

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