Palladium ethers

In a lOOmL round-bottomed flask fitted with a magnetic stirrer is placed a mixture of palladium (II) chloride (89mg, O.Smmol), p-benzoquinone (5.94g, 55mmol) and 7 1 dimethylformamide/water (20mL). To the solution, t-decene [substitute safrole for this compound) (7.0g, 50mmc4) is added in 10 min and the mixture is stirred at room temperature for 7h. The solution is poured into cold 3 normal hydrochloric acid (lOOmL) and extracted with 5 portions of ether. The extracts are combined and washed with three portions of 10% aqueous sodium hydroxide solution and a portion of brine, and then dried After removal of the solvent, the residue is distilled to give 2-decanone [P2P] yield 6.1g (78%). 

The addition of N-bromosuccinimide (1.1equiv) to a dichlo-romethane solution containing the alkene (1 equiv) and cyana-mide (4 equiv). The solution was maintained at room temperature (3 days) and then washed with water, dried, and concentrated in vacuo. Treatment of the bromocyanamide [intermediate] with 1% palladium on charcoal in methanol (1h) led to reduction of the for-madine. Addition of base to the reaction mixture (50% aqueous KOH, reflux 6h) followed by extraction with ether gave monoamine. (Yield is 48-64% final amine from alkenes analogous to safrole)... 

The benzyl group has been widely used for the protection of hydroxyl functions in carbohydrate and nucleotide chemistry (C.M. McCloskey, 1957 C.B. Reese, 1965 B.E. Griffin, 1966). A common benzylation procedure involves heating with neat benzyl chloride and strong bases. A milder procedure is the reaction in DMF solution at room temperatiue with the aid of silver oxide (E. Reinefeld, 1971). Benzyl ethers are not affected by hydroxides and are stable towards oxidants (e.g. periodate, lead tetraacetate), LiAIH, amd weak acids. They are, however, readily cleaved in neutral solution at room temperature by palladium-catalyzed bydrogenolysis (S. Tejima, 1963) or by sodium in liquid ammonia or alcohols (E.J. Rcist, 1964). 

In the prostaglandin synthesis shown, silyl enol ether 216, after transmetaJ-lation with Pd(II), undergoes tandem intramolecular and intermolecular alkene insertions to yield 217[205], It should be noted that a different mechanism (palladation of the alkene, rather than palladium enolate formation) has been proposed for this reaction, because the corresponding alkyl enol ethers, instead of the silyl ethers, undergo a similar cyclization[20I],... 

Silyl enol ethers are other ketone or aldehyde enolate equivalents and react with allyl carbonate to give allyl ketones or aldehydes 13,300. The transme-tallation of the 7r-allylpalladium methoxide, formed from allyl alkyl carbonate, with the silyl enol ether 464 forms the palladium enolate 465, which undergoes reductive elimination to afford the allyl ketone or aldehyde 466. For this reaction, neither fluoride anion nor a Lewis acid is necessary for the activation of silyl enol ethers. The reaction also proceed.s with metallic Pd supported on silica by a special method[301j. The ketene silyl acetal 467 derived from esters or lactones also reacts with allyl carbonates, affording allylated esters or lactones by using dppe as a ligand[302]... 

The cyclohexadiene derivative 130 was obtained by the co-cyclization of DMAD with strained alkenes such as norbornene catalyzed by 75[63], However, the linear 2 1 adduct 131 of an alkene and DMAD was obtained selectively using bis(maleic anhydride)(norbornene)palladium (124)[64] as a cat-alyst[65], A similar reaction of allyl alcohol with DMAD is catalyzed by the catalyst 123 to give the linear adducts 132 and 133[66], Reaction of a vinyl ether with DMAD gives the cyclopentene derivatives 134 and 135 as 2 I adducts, and a cyclooctadiene derivative, although the selectivity is not high[67]. 

Substitution at the Carbon—Chlorine Bond. Vinyl chloride is generally considered inert to nucleophilic replacement compared to other alkyl halides. However, the chlorine atom can be exchanged under nucleophilic conditions in the presence of palladium [7440-05-3] Pd, and certain other metal chlorides and salts. Vinyl alcoholates, esters, and ethers can be readily produced from these reactions. 

Aryl tetrazolyl ethers (519) are reduced by palladium on charcoal to give the arene and the tetrazolinone (520) (77AHC(2D323) this reaction is used for the removal of phenolic functionality. 

Pd-C, 1,4-cyclohexadiene, 25°, 1.5 h, 95-100% yield.Palladium black, a more reactive catalyst than Pd-C, must be used to cleave the more stable aliphatic benzyl ethers. 

The catalyst is previously prepared in an apparatus for catalytic hydrogenation, in which are placed 0.5 g. of palladous chloride, 3.0 g. of Norite, and 20 ml. of distilled water. The bottle is swept out with hydrogen and then shaken with hydrogen for 2-3 hours at 2-3 atmospheres (40 lb.) pressure. The palladium on carbon is collected on a Biichner funnel, washed with five 50-ml. portions of distilled water, then with five 50-ml. portions of 95% ethanol, and finally twice with ether. Upon drying, about 3 g. of the catalyst is obtained. It is stored in a vacuum desiccator over solid sodium hydroxide. If the reduction of the chloro-lepidine does not proceed normally, the used catalyst should be removed by suction filtration and a fresh 3-g. portion of catalyst added. Failure of the reduction step is usually due to an inactive catalyst or to impurities in the acetic acid or chlorolepidine. The palladium catalysts, prepared as described elsewhere in this volume, are presumably also satisfactory for the reduction of 2-chlorolepidine (p. 77). 

Dihydromorphinone, Cj,Hjg03N, and derivatives. Dihydromorphinone (LIII MeO HO) is formed when morphine in solution is treated with relatively large quantities of platinum or palladium catalyst under various conditions.It melts at 262-3° and yields an oxime, m.p. > 234°. The hydrochloride is the drug known as dilaudid. On 0-methyla-tion dihydromorphinone yields dihydrocodeinone (see above), and when dissolved in ether and treated with methyllithium the corresponding tertiary alcohol, 6-methyldihydromorphine, CigHggOgN, m.p. 209-211°, Wd ° 14i7° (EtOH), is formed. This on methylation with diazomethane gives 6-methyldihydrocodeine as described above (Small and Rapoport... 

Esters and amides are quite resistant to hydrogenation under almost all conditions so their presence is not expected to cause difficulties. Alkyl ethers and ketals are generally resistant to hydrogenolysis but benzyl ethers are readily cleaved, particularly over palladium or Raney nickel catalysts. ... 

The partial hydrogenation of a 17-ethynyl group over deactivated palladium occurs more readily than the saturation of any other functional group. This is also true of 17-ethynyl carbinols and 17-acetylenic ethers (52). ... 

The hydrogenation of 5a-cholestanone (58) in methanolic hydrobromic acid over platinum gives 3j5-methoxycholestane ° (61). This compound is also obtained from the palladium oxide reduction of (58) in methanol in the absence of acid. Hydrogenation of 5 -cholestanone also gives the 3j5-methoxy product under these conditions. Reduced palladium oxides are quite effective for the conversion of ketones to ethers. The use of aqueous ethanol as the solvent reduces the yield of ether. Ketals are formed on attempted homogeneous hydrogenation of a 3-keto group in methanol. ... 

Five to ten grams of the benzyl ether is hydrogenolyzed over 1-1.5 g of 5% palladium-on-charcoal in 75-100 ml of ethanol at room temperature and atmospheric pressure. Filtration and evaporation of the filtrate to dryness gives very good yields of the alcohol. ... 

Diacetato(l, 10-phenanthroline)palladium(II)-catalyzed transetheriflcation of polyfluorinated alcohols with enol ethers leads to the corresponding fluormated vinylic ethers [14] (equation 13)... 

Furukawa et al. also applied the above described palladium catalyst to the inverse electron-demand 1,3-dipolar cycloaddition of nitrones with vinyl ethers. However, all products obtained in this manner were racemic [81]. 

The reactions of nitrones constitute the absolute majority of metal-catalyzed asymmetric 1,3-dipolar cycloaddition reactions. Boron, aluminum, titanium, copper and palladium catalysts have been tested for the inverse electron-demand 1,3-dipolar cycloaddition reaction of nitrones with electron-rich alkenes. Fair enantioselectivities of up to 79% ee were obtained with oxazaborolidinone catalysts. However, the AlMe-3,3 -Ar-BINOL complexes proved to be superior for reactions of both acyclic and cyclic nitrones and more than >99% ee was obtained in some reactions. The Cu(OTf)2-BOX catalyst was efficient for reactions of the glyoxylate-derived nitrones with vinyl ethers and enantioselectivities of up to 93% ee were obtained. 

Soderberg and coworkers have developed a palladium-phosphine-catalyzed reductive iV-het-eroannuladon of 2-nitrostyrenes forming indoles in good yields For example, reaction of 6-bromo-2-nitrostyrene with carbon monoxide in the presence of a catalytic amount of palladium diacetate (6 mol% and triphenylphosphine 124 mol% in acetonitrile at 30 gives 4-bromoindole in 86% yield fEq 10 62 Several functional groups, such as esters, ethers, bromides, tnflates, and additional nitro groups, have been shown to be compatible with the reaction conditions... 

WojQo 1-4652) in absolute ethereal solution was allowed to react with palladium black. After a few hours hydrogen was passed into the liquid at ordinary temperature, giving rise to a terpene possessing the following... 

Some unsaturated compounds are capable of quantitative hydrogenation in a solution of colloidal palladium. It has been found that a hydrogen number corresponding to the iodine number of fatty oils may be ascribed to some ethereal oils. 

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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