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Silyl enol ethers palladium catalysts

Silyl enol ethers and ketene acetals derived from ketones, aldehydes, esters and lactones are converted into the corresponding o/i-unsaturated derivatives on treatment with allyl carbonates in high yields in the catalytic presence of the palladium-bis(diphenylphosphino)ethane complex (32). A phosphinc-free catalyst gives higher selectivity in certain cases, such as those involving ketene acetals. Nitrile solvents, such as acetonitrile, are essential for success. [Pg.67]

Diazonium salts react with oximes to give aryl oximes, which are easily hydrolyzed to aldehydes (R = H) or ketones." A copper sulfate-sodium sulfite catalyst is essential. In most cases higher yields (40-60%) are obtained when the reaction is used for aldehydes than for ketones. In another method for achieving the conversion ArNj —> ArCOR, diazonium salts are treated with R4Sn and CO with palladium acetate as catalyst. In a different kind of reaction, silyl enol ethers of aryl ketones, Ar C(OSiMe3)=CHR, react with sohd diazonium fluoroborates, ArNj BF4, to give ketones, ArCHRCOAr. " This is, in effect, an arylation of the aryl ketone. [Pg.938]

On the other hand, the use of [Rh(CO)2Cl]2 as a catalyst results in ring opening of the siloxycyclopropanes 13 to the silyl enol ethers 14 with high stereoselectivity [10]. The 2-siloxyrhodacyclobutane 15a is proposed to undergo j8-elimination to give jr-allylrhodium 16a followed by reductive elimination to the silyl enol ether 14a. 1-Trimethylsiloxybicyclo[n.l.0]alkanes serve as / -metallo-carbonyl compounds via desilylation with a variety of transition metals [11]. The palladium-catalyzed reaction of the siloxycyclopropanes 17 under carbon monoxide in chloroform provides a route to the 4-keto pimelates 18. In the presence of aryl triflates, the 1,4-dicarbonyl compounds 19 are... [Pg.102]

Potassium ferricyanide, 255 of silyl enol ethers and lithium enolates Iodosylbenzene, 151 Miscellaneous methods Palladium catalysts, 230 Tetrakis(trifluoroacetate)ruthenium,... [Pg.370]

In 1998, a new type of Pd(II) binuclear complex was reported which was effective for Mannich reactions of an imine derived from glyoxylate and anisidine with silicon enolates [38,39]. In these reactions, use of solvents including a small amount of water was essential. It was shown that water played an important role in this system water not only activated the Pd(II) complex to generate a cation complex, but also cleaved the N-Pd bond of the intermediate to regenerate the chiral catalyst. This reaction reportedly proceeded via an optically active palladium enolate on the basis of NMR and ESIMS analyses. A unique binuclear palladium-sandwiched enolate was obtained in the reaction of the p-hydroxo palladium complex with the silyl enol ether [(Eq. (9)]. [Pg.148]

Tanaka and co-workers <19960M1524> observed the insertion of acid chlorides into SCBs in the presence of palladium or platinum catalysts. When an excess of amine was employed, SCBs undergo ring-expansion reactions to afford cyclic silyl enol ethers in good to excellent yields (Scheme 49). [Pg.540]

In the presence of a palladium catalyst, Ar3SbX2 (X = OAc, Cl) react with silyl enol ethers in DME-MeCN at room temperature to give the corresponding a-arylketones (Equation (30)).63 When 2-furyloxytrimethylsilane is used as... [Pg.431]

Lewis acid catalysts activate the aldehyde by coordination to the carbonyl oxygen. Shibasaki et al. [13] were able to demon,strate that the activation of the enol ether is possible too. The reaction of the aldehyde 37 with the silyl enol ether 38 in the presence of the catalyst 39 proceeds with good, but still not excellent enantioselectivity to yield the aldol adduct 40. Only 5 mol % of the chiral palladium(II) complex 39 was used (Scheme 6a). Activation of the Pd(lI)-BINAP complex 39 by AgOTf is necessary. Therefore, addition of a small amount of water is important. [Pg.147]

Selective desilylation of silyl enol ethers. The silyl enol ethers of methyl ketones undergo desilylation on treatment with Bu,Snl (1 cquiv.). The reaction is markedly accelerated by a palladium catalyst, particularly PdCl2 P(o-CH,C,H4),],. The rate of desilylation is markedly decreased by steric congestion around the double bond, Thus highly selective desilylation is possible. The relative rate decreases in the following order ... [Pg.516]

Probably the most widdy applicable conditions developed for palladium catalysts utilize silyl enol ethers.In one instance,an excellent yield of enone was ob ned using 0.5 equiv. each of palla-dium(II) acetate and p-benzoquinone in acetonitrile. The method has the advantage that the position of the double bond is determine by the geometry of the precursor silyl enol ether (Scheme 26). Palla-... [Pg.141]

In the last years several publications appeared describing palladium-catalyzed a-arylations of ketone enolates for the synthesis of a-aryl ketones, involving ketone eno-lates, silyl enol ethers and intramolecular a-aiylation of ketone enolates . In this process, an enolate is generated from a ketone in the presence of an aryl halide, and a palladium catalyst couples this enolate with the aryl halide. Iwama and Rawal proposed... [Pg.368]

Cationic Pd complexes can be applied to the asymmetric aldol reaction. Shibasaki and coworkers reported that (/ )-BINAP PdCP, generated from a 1 1 mixture of (i )-BINAP PdCl2 and AgOTf in wet DMF, is an effective chiral catalyst for asymmetric aldol addition of silyl enol ethers to aldehydes [63]. For instance, treatment of trimethylsi-lyl enol ether of acetophenone 49 with benzaldehyde under the influence of 5 mol % of this catalyst affords the trimethylsilyl ether of aldol adduct 113 (87 % yield, 71 % ee) and desilylated product 114 (9 % yield, 73 % ee) as shown in Sch. 31. They later prepared chiral palladium diaquo complexes 115 and 116 from (7 )-BINAP PdCl2 and (i )-p-Tol-BINAP PdCl2, respectively, by reaction with 2 equiv. AgBF4 in wet acetone [64]. These complexes are tolerant of air and moisture, and afford similar reactivity and enantioselec-tivity in the aldol condensation of 49 and benzaldehyde. Sodeoka and coworkers have recently developed enantioselective Mannich-type reactions of silyl enol ethers with imi-nes catalyzed by binuclear -hydroxo palladium(II) complexes 117 and 118 derived from the diaquo complexes 115 and 116 [65]. These reactions are believed to proceed via a chiral palladium(fl) enolate. [Pg.593]

Similar 1,4-bis-silylation of a,p-unsaturated ketones with 32 is catalyzed by the isonitrile-palladium catalyst 34 to afford seven-membered ring silyl enol ether 69 in high yields (Eq. 35). Reactions of 32 with acrylic esters and acrylonitrile, however, give five-membered products 70 [20,30]. [Pg.146]

The search for a catalyst suitable to promote addition of the less reactive silyl enol ethers of ketones has identified a novel class of cationic transition metal complexes in two independent laboratories. The use of a chiral palladium(II) di-aquo complex in the catalytic asymmetric addition of silyl enol ethers to aldehydes (first demonstrated by Shibasaki, Sodeoka et al. [52a, 52b]) provided a clear precedent for their subsequent use with a-imino esters [53] (Scheme 27). Initial experiments focused on the reaction of various a-imino esters 82a-c with silyl enol ether 83 (1.5equiv) in the presence of the Pd diaquo complex 80a (10 mol %) in DMF. Extensive experimentation led to the formation of 84c in 67% ee, and also underscored the importance of suppressing the generation of tetrafluoroboric acid during the course of the reaction. [Pg.906]

Nakai and a coworker achieved a conceptually different protonation of silyl enol ethers using a chiral cationic palladium complex 40 developed by Shibasaki and his colleagues [61] as a chiral catalyst and water as an achiral proton source [62]. This reaction was hypothesized to progress via a chiral palladium enolate which was diastereoselectively protonated by water to provide the optically active ketone and the chiral Pd catalyst regenerated. A small amount of diisopropylamine was indispensable to accomplish a high level of asymmetric induction and the best enantioselectivity (79% ee) was observed for trimethylsilyl enol ether of 2-methyl-l-tetralone 52 (Scheme 11). [Pg.1230]

In one example particular stereochemical issues were addressed. Silyl enol ether 77 undergoes palladium-catalyzed 1,6-ECRC with a modest level of stereoinduction to afford a diastereomer-ic mixture [d.r. eisl trails) 2 1], These initial results should stimulate further investigation into transition-metal-catalyzed ECRCs and have the potential for future development of chiral metal catalysts for such processes. [Pg.541]

An alternative approach to the protonation of silyl enol ethers involves the use of palladium catalysts which proceed via intermediate palladium enolates. The asymmetry can either be provided by ligands on the palladium or from an enantiomerically pure acid. °... [Pg.338]

Takasago Perfumery Ltd. manufactures optically pure (Jl)-muscone from the racemic compound by way of its silyl enol ether which is dehydrosUylated with palladium acetate to the pure (Z)-enone. [202] The enantioselective hydrogenation with ruthenium-BINAP catalysts finally gives the enantiomericaUy pure product. [203]... [Pg.138]


See other pages where Silyl enol ethers palladium catalysts is mentioned: [Pg.104]    [Pg.85]    [Pg.111]    [Pg.109]    [Pg.326]    [Pg.286]    [Pg.206]    [Pg.59]    [Pg.725]    [Pg.7]    [Pg.7]    [Pg.352]    [Pg.541]    [Pg.516]    [Pg.144]    [Pg.6587]    [Pg.144]    [Pg.7]    [Pg.617]    [Pg.628]    [Pg.1089]    [Pg.6586]    [Pg.195]    [Pg.144]   
See also in sourсe #XX -- [ Pg.141 ]

See also in sourсe #XX -- [ Pg.141 ]

See also in sourсe #XX -- [ Pg.7 , Pg.141 ]

See also in sourсe #XX -- [ Pg.7 , Pg.141 ]

See also in sourсe #XX -- [ Pg.141 ]




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Enolates silylation

Palladium catalysts catalyst

Palladium enolate

Palladium enolates

Palladium ethers

Silyl enol ethers

Silyl enol ethers catalysts

Silyl enolate

Silyl enolates

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