Palladium catalyst vinyl substitutions

Aryl halides which are rather inert in usual organic reactions can undergo reactions by means of palladium catalysts. Thus, styrene and stilbene derivatives are obtained by reaction of olefins with aryl bromides at 125 °C using Pd(0Ac)2 (1 mol%) and tri-(o-tolyl)phosphine (2 mol%)83. The palladium-catalyzed vinylic substitution reaction is applicable to a variety of heterocyclic bromides including pyridine, thiophene, indole, furan, quinoline and isoquinoline84. Thus, reaction of 3-bromopyri-dine with l-(3-butenyl)phthalimide at 100 °C gives l-[4-(3 -pyridyl)-3-butenyl]-phthalimide (yield of mixed amine 57%, selectivity 68%) at 100 °C. This phthalimide is subsequently converted to nornicotine (188) (Scheme 59). The reaction of acrylic... 

Contrasting results are obtained for the peralkylated disilanes RMe2SiSi-Me2R (R = Me, "Bu, Bu), which yield only trace amounts of the 1,4-addition products under the same reaction conditions. Attempts to increase double silylation yields by use of other platinum or palladium catalyst precursors under carbon monoxide pressure or inert atmosphere were also unsuccessful for these peralkylated disilanes. Additionally, the reaction of tetramethyl-l,2-divinyldisilane results in conversion to an intractable product mixture, with no incorporation of the 1,3-diene. Phenyl-substituted disilanes are also effective reagents in the Pt(dba)2-catalyzed double silylation of phenylacetylene, but again, the alkylated disilanes and the vinyl-substituted disilane do not give double silylation products. 

Oxidative coupling of specific alkenes such as styrene derivatives459 and vinyl acetate460 to 1,3-diene derivatives can also be achieved in the presence of palladium catalysts.367,455 This coupling essentially occurs head to head , i.e. the C—C bond formation involves the least substituted carbon atoms of the double bonds (equation 188).461... 

Triarylphosphines, which are often employed with palladium in catalysts, also can transfer aryl groups to the palladium and cause vinyl substitution reactions with alkenes.49,30 Fortunately, this reaction is usually slower than other methods for generating arylpalladium derivatives so that it usually is not a problem, but there are exceptions (equation 16). 

The same reactions, carried out with potassium carbonate as base in place of a secondary amine, yield exocyclic dienes in good yield, although double-bond isomerization sometimes occurs (equation 38).93 Inclusion of tetra-zi-butylammonium chloride in the reaction mixture stops the double-bond isomerization. Thus, the reaction in equation (38) with the chloride yields only the bis(exomethylene) product in 45% yield in a slow reaction. Some N- and O-heterocyclic products, also, have been prepared by the intramolecular vinyl substitution reaction.94 A 16-membered ring lactone was made by the ring closure of a vinylic iodide group with a vinyl ketone group. The yield, based upon the reactant, was 55% but a stoichiometric amount of bis(acetonitrile)palladium dichloride was employed. The catalyst was prereduced with formic acid so that the reaction proceeded at 25 C (equation 39).95... 

The palladium-catalyzed fixation of C02 is also a useful method for the synthesis of CCs, with the first such example using vinyl-substituted epoxides and a palladium catalyst [Pd(PPh3)4/PPh3] having been reported independently by both Fujinami and Trost [147, 148]. Here, the carbonate is produced via the formation of a first tr-allyl-palladium intermediate (I) this then fixes C02 to form a second tr-allyl-intermediate (II) that produces vinyl-substituted cyclic carbonates (Scheme 7.8). 

There are scattering examples that neutral organosilanes R-SiMe3 undergo a desilylative coupling reaction with aryl halides in the presence of a palladium catalyst. Hallberg and his co-workers disclosed that trimethyl(vinyl)silane reacts with an arylpalladium(II) complex to afford coupled products accompanied by aryl-substituted alkenylsilanes formed through the Heck type reaction... 

In the presence of a fluoride ion generating reagent such as tris(diethylamino)sulfonium difluorotri-methylsilicate (TASF, 99) and a palladium catalyst, vinyltrimethylsilane couples with vinyl and aryl iodides." For substituted vinylsilanes, the fluorodimethylsilyl group is particularly effective in the coupling reaction, which takes place with retention of configuration of both substrates (Scheme 17). Silicon-based C—C bond formation is as useful as that which employs organoborons " for the synthesis of stereo-defined conjugated dienes. 

Alkynes react with thiols to give vinyl sulfides. With alkynes it is possible to add 1 or 2 equivalents of RSH, giving a vinyl sulfide or a dithioketal, respectively. Alternative preparations are available, as in the reaction of a terminal alkyne with Cp2Zr(H)Cl followed by PhSCl to give the vinyl sulfide with the SPh unit at the less substituted position (PhCH=CHSPh). The intramolecular addition of a thiol to an ene-yne, with a palladium catalyst, leads to substituted thiophene derivatives. ... 

Phenyl, vinyl or carbonyl substituted cyclopropanes are more easily hydrogenolyzed than are the alkyl substituted species. Such compounds are commonly cleaved over palladium catalysts at room temperature and atmospheric pressure. Hydrogenolyses run over platinum, rhodium or nickel catalysts frequently result in the saturation of the double bond, the benzene ring or the carbonyl group with the cyclopropane ring remaining intact or cleaved to only a slight extent. 20 As illustrated in Fig. 20.22 the bond broken in the... 

On treatment with a palladium(O) catalyst, vinyl epoxides undergo facile unimolecular rearrangement to give dienols or enones depending on the substitution pattern of the substrate. In the presence of an active methylene compound in the reaction system, however, a single alkylation product is formed. Cyclic and acyclic vinyl epoxides participate equally well. The reaction proceeds with clean alkylation from the same face as the oxygen of the epoxide, and proceeds with allyl inversion (Scheme 22). ... 

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