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Palladium alkenylation

Yamamoto has proposed a mechanism for the palladium-catalyzed cyclization/hydrosilylation of enynes that accounts for the selective delivery of the silane to the more substituted C=C bond. Initial conversion of [(77 -C3H5)Pd(GOD)] [PF6] to a cationic palladium hydride species followed by complexation of the diyne could form the cationic diynylpalladium hydride intermediate Ib (Scheme 2). Hydrometallation of the less-substituted alkyne would form the palladium alkenyl alkyne complex Ilb that could undergo intramolecular carbometallation to form the palladium dienyl complex Illb. Silylative cleavage of the Pd-G bond, perhaps via cr-bond metathesis, would then release the silylated diene with regeneration of a palladium hydride species (Scheme 2). [Pg.370]

The first palladium alkenyls, pzTpPd C,N-C(Cl) CHCMe2NMe2 (484)144 and the 3-oxo-hexenyl complex 493,160 were obtained systematically by halide displacement and dimer cleavage (Scheme 36). In common with alkyl and aryl systems (462—479, Section III.C.3), the pzTp ligand was in each case concluded to adopt a -coordination mode in solution, on the basis of (i) spectroscopic data, (ii) literature precedent, and (iii) the assumption that the Pd(II) centers in these complexes were too electron rich to permit coordination of the third pyrazole no solid-state data were reported. Both materials are fluxional in solution, and for 484 the slow-exchange limit was attained at —30 °C, with equilibration of the pyrazolyl environments becoming rapid at 79 °C, though the fast exchange limit... [Pg.168]

This implies that the other elementary steps in cycle B (Scheme 1), i.e., Pd-carbomethoxy formation and protonolysis of the palladium-alkenyl species, must even be considerably faster than the observed overall high reaction rate. A high rate of Pd-carbomethoxy formation (at equilibrium) could be expected for the strongly electrophilic metal center. However, the latter step, protonolysis of the Pd-alkenyl bond in l-palladium-2-carbomethoxypropene and 2-palladium-1-car-bomethoxypropene, respectively, is expected to be a slow reaction, because the proton has to overcome a relatively high barrier of (electrostatic) repulsion by the cationic palladium center on its way to the palladium-carbon bond. [Pg.324]

It is assumed that a ligand protonated at the pyridyl group (P-NH" ), and mono-coordinated via phosphorus to the palladium center, fulfills a key role as a proton messenger , by bringing the proton into very close proximity with the coordination sphere at the palladium-alkenyl bond (Scheme 3). [Pg.324]

Molecular modeling of the P-NH" coordinated complex indeed suggests that the proton can point into the /r-electron cloud of the Pd-alkenyl moiety, bringing the proton right to the spot for protonolysis of the palladium-alkenyl bond. This can be seen as lowering the entropy barrier of activation in the protonolysis step. The... [Pg.324]

Palladium-catalyzed trimerization of alkynes has been developed, " but simple terminal alkynes undergo dimerization to form enynes. A mechanism for the formation of head-o-tail enynes has been proposed that proceeds through palladium(iv) complexes 202 or 203. Probably, however, the acidic terminal alkyne will cleave the palladium-alkenyl bond to give the enyne product and an alkynylpalladium(ii) species that can enter a new catalytic cycle instead." ... [Pg.305]

Vinyl acetate reacts with the alkenyl triflate 65 at the /3-carbon to give the 1-acetoxy-1,3-diene 66[68]. However, the reaction of vinyl acetate with 5-iodo-pyrimidine affords 5-vinylpyrimidine with elimination of the acetoxy group[69]. Also stilbene (67) was obtained by the reaction of an excess of vinyl acetate with iodobenzene when interlamellar montmorillonite ethylsilyl-diphenylphosphine (L) palladium chloride was used as an active catalyst[70]. Commonly used PdCl2(Ph3P)2 does not give stilbene. [Pg.138]

In the reaction of aryl and alkenyl halides with 1,3-pentadiene (248), amine and alcohol capture the 7r-allylpalladium intermediate to form 249. In the reactions of o-iodoaniline (250) and o-iodobenzyl alcohol (253) with 1,3-dienes, the amine and benzyl alcohol capture the Tr-allylpalladium intermediates 251 and 254 to give 252 and 255[173-175]. The reaction of o-iodoaniline (250) with 1,4-pen tadiene (256) affords the cyclized product 260 via arylpalladiuni formation, addition to the diene 256 to form 257. palladium migration (elimination of Pd—H and readdition to give 258) to form the Tr-allylpalladium 259, and intramolecular displacement of Tr-allylpalladium with the amine to form 260[176], o-Iodophenol reacts similarly. [Pg.164]

Allenes also react with aryl and alkenyl halides, or triflates, and the 7r-allyl-palladium intermediates are trapped with carbon nucleophiles. The formation of 283 with malonate is an example[186]. The steroid skeleton 287 has been constructed by two-step reactions of allene with the enol trillate 284, followed by trapping with 2-methyl-l,3-cyclopentanedione (285) to give 286[187]. The inter- and intramolecular reactions of dimethyl 2,3-butenylmalonate (288) with iodobenzene afford the 3-cyclopentenedicarboxylate 289 as a main product) 188]. [Pg.167]

Hydrogenolysis of aryl and alkenyl halides and triflates proceeds by the treatment with various hydride sources. The reaction can be explained by the transmetallation with hydride to form palladium hydride, which undergoes reductive elimination. Several boro hydrides are used for this purpose[680], Deuteration of aromatic rings is possible by the reaction of aryl chlorides with NaBD4681]. [Pg.248]

Ketones can be prepared by trapping (transmetallation) the acyl palladium intermediate 402 with organometallic reagents. The allylic chloride 400 is car-bonylated to give the mixed diallylic ketone 403 in the presence of allyltri-butylstannane (401) in moderate yields[256]. Alkenyl- and arylstannanes are also used for ketone synthesis from allylic chlorides[257,258]. Total syntheses of dendrolasin (404)f258] and manoalide[259] have been carried out employing this reaction. Similarly, formation of the ketone 406 takes place with the alkylzinc reagent 405[260],... [Pg.343]

Alkenyl zirconium complexes derived from alkynes form C—C bonds when added to aHyUc palladium complexes. The stereochemistry differs from that found in reactions of corresponding carbanions with aHyl—Pd in a way that suggests the Cp2ZrRCl alkylates first at Pd, rather than by direct attack on the aUyl group (259). [Pg.440]

There are reports of an increasing number of palladium-assisted reactions, in some of which the palladium has a catalytic function. Thus furan and thiophene undergo facile palladium-assisted alkenylation giving 2-substituted products. Benzo[6 Jfuran and TV- acetyl-indole yield cyclization products, dibenzofurans and carbazoles respectively, in addition to alkenylated products (8UOC851). The arylation of pyrroles can be effected by treatment with palladium acetate and an arene (Scheme 86) (81CC254). [Pg.83]

PALLADIUM-CATALYZED REACTION OF ORGANOLITHIUM COMPOUNDS AND ALKENYL HALIDES ... [Pg.44]

Allylation of perfluoroalkyl halides with allylsilanes is catalyzed by iron or ruthenium carbonyl complexes [77S] (equation 119) Alkenyl-, allyl-, and alkynyl-stannanes react with perfluoroalkyl iodides 111 the presence ot a palladium complex to give alkenes and alkynes bearing perfluoroalkyl groups [139] (equation 120)... [Pg.478]

Heck reaction, palladium-catalyzed cross-coupling reactions between organohalides or triflates with olefins (72JOC2320), can take place inter- or intra-molecularly. It is a powerful carbon-carbon bond forming reaction for the preparation of alkenyl- and aryl-substituted alkenes in which only a catalytic amount of a palladium(O) complex is required. [Pg.22]

Palladium-catalyzed carbon-carbon bond forming reactions like the Suzuki reac-tion as well as the Heck reaction and the Stille reaction, have in recent years gained increased importance in synthetic organic chemistry. In case of the Suzuki reaction, an organoboron compound—usually a boronic acid—is reacted with an aryl (or alkenyl, or alkynyl) halide in the presence of a palladium catalyst. [Pg.272]

The electrophilic character of the palladium atom in the complexes formed by oxidative addition of aryl halides and alkenyl halides to palladium(o) complexes can be exploited in useful ways. [Pg.573]

Hydroxy-l-alkenyl diisopropylcarbamates 2 (X = OCb), in this respect, occupy a medium position since they are stable in strongly acidic and basic protic solvents. For deblocking vinyl carbamates, the presence of catalytic amounts of mercuric or palladium(II) salts is required. Due to this stability, several reactions of homoallylic alcohols, proceeding with high diastereo-selectivity, e g., epoxidation, are applicable in order to introduce further hetero-substituents. [Pg.227]

The coupling reaction of aryl-alkenyl halides with alkenes in the presence of a palladium catalyst and a base is known as the Heck coupling (Scheme 9.4).6 Since the early 1980s, this type of coupling reaction has been used for die syndiesis of poly(arylenevinylene) and related polymers by polymerization of AB- or AA/BB-type of monomers (Scheme 9.5).7... [Pg.468]

Polymerization using the Stille coupling, the cross-coupling of aryl-alkenyl halides with organotins in the presence of palladium catalysts (Scheme 9.10),13 appeared in 1989 (Scheme 9.11).14 The low nucleophilicity of organotins makes it possible to use functionalized monomers for the polymerization.15... [Pg.470]

At about die same time, die application of the Suzuki coupling, the crosscoupling of boronic acids widi aryl-alkenyl halides in die presence of a base and a catalytic amount of palladium catalyst (Scheme 9.12),16 for step-growth polymerization also appeared. Schliiter et al. reported die synthesis of soluble poly(para-phenylene)s by using the Suzuki coupling condition in 1989 (Scheme 9.13).17 Because aryl-alkenyl boronic acids are readily available and moisture stable, the Suzuki coupling became one of die most commonly used mediods for die synthesis of a variety of polymers.18... [Pg.470]

Organotins. The organotin reagents have much lower nucleophilicity than that of the Grignard reagents, thus allowing the use of a variety of functionalized monomers for the polymerization. Aryl-alkenyl iodides, bromides and tosylates have been used as substrates. Palladium complexes are commonly employed as catalysts for the reaction. Because the catalysts can be destroyed... [Pg.484]

Reduction of iV-(3-bromopropyl) imines gives a bromo-amine in situ, which cyclizes to the aziridine. Five-membered ring amines (pyrrolidines) can be prepared from alkenyl amines via treatment with N-chlorosuccinimide (NCS) and then BusSnH. " Internal addition of amine to allylic acetates, catalyzed by Pd(PPh3)4, leads to cyclic products via a Sn2 reaction. Acyclic amines can be prepared by a closely related reaction using palladium catalysts. Three-membered cyclic amines (aziridines)... [Pg.500]


See other pages where Palladium alkenylation is mentioned: [Pg.324]    [Pg.259]    [Pg.260]    [Pg.272]    [Pg.174]    [Pg.324]    [Pg.259]    [Pg.260]    [Pg.272]    [Pg.174]    [Pg.126]    [Pg.168]    [Pg.187]    [Pg.238]    [Pg.315]    [Pg.316]    [Pg.184]    [Pg.35]    [Pg.35]    [Pg.45]    [Pg.566]    [Pg.567]    [Pg.587]    [Pg.484]    [Pg.485]    [Pg.485]    [Pg.24]    [Pg.29]    [Pg.785]    [Pg.1003]    [Pg.1036]   
See also in sourсe #XX -- [ Pg.463 , Pg.464 , Pg.465 , Pg.466 , Pg.489 ]

See also in sourсe #XX -- [ Pg.537 ]




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Alkenyl palladium compound

Alkenylations pyrroles, palladium acetate

Alkynes palladium-catalyzed reaction with alkenyl halides

Aryl-alkenyl cross-coupling, palladium-catalyzed

Aryl-alkenyl cross-coupling, palladium-catalyzed examples

Aryl-alkenyl cross-coupling, palladium-catalyzed reactions

Aryl-alkenyl cross-coupling, palladium-catalyzed scope

Benzyl-alkenyl cross-coupling, palladium-catalyzed

Benzyl-alkenyl cross-coupling, palladium-catalyzed benzylation

Ei-ichi Negishi and Show-Yee Liou 5 Palladium-Catalyzed Substitution Reactions of Alkenyl Epoxides

Halides palladium-catalyzed alkenylation

Halides palladium-catalyzed coupling with alkenyl

Halides palladium-catalyzed reaction with alkenyl

Palladium acetate alkenylation

Palladium alkenyl species

Palladium alkenyl-alkynyl reactions

Palladium alkenyl-aryl reactions

Palladium alkenylation reactions

Palladium alkynyl-alkenyl coupling

Palladium catalysis alkenylation

Palladium-catalyzed alkenyl epoxide

Palladium-catalyzed alkenylation

Palladium-catalyzed alkenylation and arylation

Stannanes palladium-catalyzed coupling with alkenyl

Trifluoromethanesulfonates palladium-catalyzed reaction with alkenyl

Zinc, alkynylchlororeaction with alkenyl halides palladium-catalyzed

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