Isomerization iridium catalysts

Iron-sulfur cluster compounds, 1203 dinuclear, 235 electrochemistry, 236 hexanuclear, 241 mononuclear, 235 tetranuclear, 238 trinuclear, 237 Isomerization iridium catalysts, 1158... 

A polymer-supported iridium catalyst 4 has been prepared and used in the isomerization of the double bonds in aryl allyl ethers and aryl allylic compounds with excellent trans-scIcctivity and without conventional workup procedures (Scheme 45).73... 

The isomerization of propargylic alcohols to a,/3-enones was also developed by using an iridium catalyst. A variety of secondary propargylic alcohols can be isomerized to the corresponding a,/3-unsaturated ketones in the presence of 1 mol% IrHs(Pr 3P)2 (Scheme 54).93... 

Hartwig and coworkers reported an approach to address this limitation involving tandem catalytic reactions. In this tandem process, sequential palladium-catalyzed isomerization of the branched isomer to the linear isomer, followed by iridium-catalyzed allylic substitution leads to the branched product with high enantiomeric excess [105]. More specifically, treatment of branched allylic esters with catalytic amounts of the combination of Pd(dba)2 and PPhs led to rapid isomerization of the branched allylic ester to the linear isomer, and the linear isomer underwent allylic substitution after addition of the iridium catalyst and nucleophile (Scheme 31). 

Fig. 4.5 Polymer-supported iridium catalysts (61) and (62) for the isomerization of olefinic double bonds.

The preparation of polymer-supported iridium catalysts (61) and (62) for the stereoselective isomerization of double bonds using polystyrene based immobilized triphenyl phosphine were recently reported by Ley and coworkers (Fig. 4.5). The immobilized catalyst is potentially useful for deprotection strategies of aUyl ethers [130]. 

Hydrosilylations. Addition of triethylsilane across multiple bonds occurs under the influence of a large number of metal catalysts. Terminal alkynes undergo hydrosilylations easily with triethylsilane in the presence of platinum, rhodium, ruthenium, osmium, or iridium catalysts. For example, phenylacety-lene can form three possible isomeric hydrosilylation products with triethylsilane the (Z)-/3-, the and the a-products... 

IrH2( /i/)2i 2]A systems, prepared in situ, are effective in the isomerization of allylic alcohols to carbonyl compounds, " and isomerization is always a side reaction in hydrogenation reactions with the iridium catalyst. 

Miyaura has reported the iridium-catalyzed isomerization of unsymmetrical dia-Uyl ethers to ( )-allyl vinyl ethers [20]. The iridium catalyst 12 active for the isomerization of diallyl ethers was prepared in situ by bubbhng hydrogen into a red solution of [Ir(cod)(PPh2Me)2]PF(5 by the method reported by FeUdn (Eq. 3.1.11)... 

The cinnamyl ethers were treated with an iridium catalyst to furnish the corresponding vinyl ethers (Eq. 3.1.12). The utility of this catalyst was demonstrated in the stereoselective synthesis of aUyl vinyl ethers. 2,3,3-Trimethyl-4-pentenal was obtained in 51% yield when the isomerization of the diaUyl ether to give the aUyl vinyl ether was followed by heating to proceed the Claisen rearrangement (Eq. 3.1.13). 

Obtained by isomerization of l-[3-hydroxy-4-(2-propenyl)phenyl]ethanone in the presence of polymer-supported iridium catalyst in THF at r.t. 

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). 

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