Palladium catalysts conjugated dienes

The groups R2N and Cl can be added directly to alkenes, allenes, conjugated dienes, and alkynes, by treatment with dialkyl-V-chloroamines and acids. " These are free-radical additions, with initial attack by the R2NH- radical ion. " N-Halo amides (RCONHX) add RCONH and X to double bonds under the influence of UV light or chromous chloride. " Amines add to allenes in the presence of a palladium catalyst. ... 

The hydrosilation of butadiene, isoprene and other simple conjugated dienes with platinum catalysts has not been intensively studied. It usually occurs by 1,4 addition and only at elevated temperatures (10). Although palladium catalysts are practically ineffective to hydrosilate an alkene, they are very active under mild conditions with conjugated dienes to give two principal products, sometimes in 100% yields. With triethoxy silane, butadiene, and PdCl2(PhC=N)2 (5.5 x 103 moles/mole) at 22°C for 24... 

A mild aerobic palladium-catalyzed 1,4-diacetoxylation of conjugated dienes has been developed and is based on a multistep electron transfer46. The hydroquinone produced in each cycle of the palladium-catalyzed oxidation is reoxidized by air or molecular oxygen. The latter reoxidation requires a metal macrocycle as catalyst. In the aerobic process there are no side products formed except water, and the stoichiometry of the reaction is given in equation 19. Thus 1,3-cyclohexadiene is oxidized by molecular oxygen to diacetate 39 with the aid of the triple catalytic system Pd(II)—BQ—MLm where MLm is a metal macrocyclic complex such as cobalt tetraphenylporphyrin (Co(TPP)), cobalt salophen (Co(Salophen) or iron phthalocyanine (Fe(Pc)). The principle of this biomimetic aerobic oxidation is outlined in Scheme 8. 

The consecutive reaction of vinyl halides and alkenes with activated methylene systems [42] in the presence of a palladium catalyst and phase-transfer catalyst results from the addition of the methylene carbanion with the initially formed Heck product (Scheme 6.31) an intramolecular version of the reaction leads to the formation of bicycloalk-l-enes (Scheme 6.31) [42], The analogous combined coupling reaction of iodoarenes and activated methylene compounds with non-conjugated dienes under similar conditions forms the monoalkene (Scheme 6.31) [43]. 

Vinyl iodide coupled to 1 gave the rather sensitive and reactive cross-conjugated diene 243 in 37-43% yield. When a dienophile 244-R was added to the reaction mixture prior to work-up, the corresponding monoadducts of type 247 were isolated in 15-65% yield. Heating a mixture of 1, vinyl iodide, and a dienophile 244-R in the presence of palladium catalyst yielded the corresponding bisadducts 250 resulting from a domino Diels-Alder addition onto the cross-conjugated triene 243 (Scheme 57) [147,148]. 

A few experiments have been tried with conjugated dienes in the substitution reaction. Preliminary results indicate that they too may react normally. Using palladium acetate in a stoichiometric reaction, benzene and butadiene were found to form 1-phenylbutadiene in about 25% yield (41). Iodobenzene and isoprene react with triethylamine and Pd(PPh3)2(OAc)2 as catalyst at 100° to form ( )-3-methyl-l-phenyl-1, 3-butadiene in 52% yield (42) ... 

Palladium(II)-promoted oxidative 1,4-difunctionalization of conjugated dienes with various nucleophiles is a useful reaction [98], The reaction is stoichiometric with respect to Pd(II) salts, but it can be made catalytic by use of Pd(0) reoxidants. 1,4-Difunctionalization with the same or different nucleophiles has wide synthetic application. The oxidative diacetoxylation of butadiene with Pd(OAc)2 proceeds by acetoxypalladation to generate the 7i-allylpalladium 136, which is attacked by acetoxy anion as the nucleophile, and (E)-, 4-diacctoxy-2-butcnc (137) is formed with 3,4-diacetoxy-1-butene (138) as the minor product. The commercial process for 1,4-diacetoxy-2-butene (137) by the reaction of butadiene, AcOH and O2 has been developed using a supported Pd catalyst containing Te. 1,4-Butanediol (139) and THF are produced commercially from l,4-diacetoxy-2-butene (137) [99]. 

Pennequin I, Mortreux A, Petit F, Mentech J, Thiriet B (1994) Telomerisation of conjugated diene with sugar (derivs.) - by a reaction in aq. soln. and in the presence of a palladium catalyst and a ligand. FR 2693188... 

Catalytic hydroboration is a new methodology of great synthetic potential. The reaction is usually carried out with catecholborane in the presence of rhodium, palladium, iridium and ruthenium compounds.2 In contrast to olefins, very little is known on catalytic hydroboration of conjugated dienes and enynes. Our earlier studies on the uncatalyzed monohydroboration of conjugated dienes,6 reports on the hydroboration of 1-decene with catecholborane catalyzed by lanthanide iodides,7 and monohydroboration of 1,3-enynes in the presence of palladium compounds,8 prompted us to search for other transition metal catalysts for monohydroboration of conjugated dienes and enynes 9 10... 

The hydrogenation of conjugated dienes to monoalkenes poses questions of both regio- and stereoselectivity and is a function of the metal and the conditions.The distribution of products depends not only on the inherent selectivity of the initial addition process but also on the competition between the diene and the first-formed alkene(s) for the reactive sites. The latter may add hydrogen or be isomerized. If the structure of the diene allows the change, the diene itself may be isomerized. As for alkynes, palladium and nickel catalysts tend to be the most selective to the monoene. 

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. 

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