Aldehydes palladium® acetate

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. 

Mixtures of regioisomers are frequendy obtained in these reactions.80 The problem is most serious with primary allylic alcohols without a- or p-substituents. Even the 2-arylated products generally rearrange to saturated aldehydes. Ally alcohol itself, when reacted with iodobenzene and triethylamine, with palladium acetate as catalyst, for example, produces a 71 % yield of an 84 16 mixture of 3-phenyl- and 2-phenyl-propanal (equation 28). 

In accessing chiral allyl vinyl ethers for Claisen rearrangement reactions, Nelson et al. employed the iridium-mediated isomerization strategy. Thus, the requisite enantioenriched diallyl ether substrate 28 was synthesized via a highly enantioselective diethylzinc-aldehyde addition protocol10 (Scheme 1.1k). The enantioselective addition of Et2Zn to cinnamaldehyde catalyzed by (—)-3-exo-morpholinoisobomeol (MIB 26)11 provided an intermediate zinc alkoxide (27). Treatment of 27 with acetic acid followed by 0-allylation in the presence of palladium acetate delivered the 28 in 73% yield and 93% ee. Isomerization of 28 with a catalytic amount of the iridium complex afforded the allyl vinyl ether... 

CONJUGATE ADDITION (3-Bromopropion-aldehyde ethylene acetal. 1-r-Butylthio-1 -trimethylsilyloxyethylene. Cryptates. l-EthylsuIfinyl-3-pentanone. HexamethyF phosphoric triamide. Ketene bis-(methylthio)ketal monoxide. Organo-lithiuni compounds. Palladium(II) chloride. Phase-transfer catalysts. 

A chiral oxazolidine prepared from a,j6-unsaturated aldehydes and ( —)- or (-l-)-ephedrine efficiently induced asymmetric cyclopropanation with excess of diazomethane in the presence of palladium acetate, e.g. formation of 24 from ( —)-ephedrine and ( )-cinnamaldehyde 24 was cyclopropanated to give 25 and the auxiliary removed giving... 

Efficient cycloadditions to aldehydes can be achieved by employing a cocatalyst in conjunction with the standard catalyst system30. Suitable cocatalysts are tributyltin acetate (20-40 mol%) or trimethyltin acetate (5-10 mol%) and the catalyst system itself is that derived from palladium acetate (5mol%) and triphenylphosphane (25 mol%) in tetrahydrofuran. 

In his pioneering contributions Moiseev has shown that giant cationic palladium clusters , e.g. Pd56iL6o(OAc)i8o (L = phenanthroline, bipyridine), characterized by use of high-resolution TEM, SAXS, EXAFS, IR and magnetic susceptibility data, catalyze, under mild conditions (293 363 K, 1 bar), the oxidative acetoxylation of ethylene into vinyl acetate, propylene into allyl acetate, and toluene into benzyl acetate. The oxidation of primary aliphatic alcohols to esters, and the conversion of aldehydes into acetals were also studied. ... 

The same transformations can he effected by reaction of the trialkylsilyl enol ether of the aldehydes or ketones with palladium acetate. For example, treatment of the trimethylsilyl enol ether of cyclooctanone with 10 mol% Pd(OAc)2 in DMSO under one atmosphere of oxygen at 25 °C for 12 h gave cyclooctenone (82% yield). 

Two slightly different methodologies have been reported for the use of catalytic palladium acetate in the oxidation of alcohols, which interestingly give quite different selectivities. Thus, when iodobenzene is used as re-oxidant in a buffered phase transfer system modest to quantitative gas chromatographic yields of aldehydes or ketones are obtained from... 

Condensations between ethyl isocyanoacetate and unsaturated aldehyde (or ketones) in the presence of ZnCl2 or CuCl-Et N lead to oxazolines (522) in variable yields (29-95%). " Subsequent treatment with 2.5 mol% of palladium acetate and PPh (THF, 20 °C) gives excellent yields of the formamido-dienoates (523). The mechanism probably involves initial oxidative addition of the... 

Examples of the formylation of aryl halides with synthesis gas catalyzed by palladium complexes are summarized in Equation 19.90. These reactions relied upon the development of ligands with particular steric and electronic properties. The dia-damantyl-n-butyl phosphine shown in the equation, in combination with palladium acetate, leads to the formation of aromatic aldehydes in high yields from electron-rich and electron-poor aryl bromides. Reactions of nitroarenes and 2-bromopyridine provided the aldehydes in low yield, but other examples occurred in satisfactor) yield with only 0.1-0.75 mol % catalyst. The identity of the base is important in this process, and TMEDA was the most effective base. The mechanism of this process was not proposed in the initial work, but is likely to occur by oxidative addition of the aryl halide, insertion of the carbon monoxide into the palladium-aryl bond, and a combination of hydrogenolysis of the acyl intermediate and elimination of hydrogen halide to regenerate palladium(O). The base would then be involved in the hydrogenol5 sis and consumption of hydrogen halide. 

One of the traditional methods for applications of the aliphatic Claisen rearrangement has used Mercuric salts to prepare vinyl ether as illustrated in the use of the allylic alcohol (28) en route to aldehyde 29. The chemical development group at Boehringer-Ingelheim has developd a mild palladium acetate-phenanthroline catalyst 31 for the sequential allyl vinyl ether-Claisen process utilizing commercially available triethyleneglycol divinyl ether which avoids the use of mercuric acetate. ... 

Enol esters (126) can be formed in >70% yields during condensations between thioesters (125) and aldehydes (R CH2CHO) in the presence of caesium fluoride. An alternative approach to esters (126) is to react vinylmercurials, e.g. (127), with mercury carboxylates [(R C02)2Hg] and a catalytic quantity of palladium acetate. A wide range of the organometallic reagents (127) can be obtained from acetylenes by a hydroboration-mercuration sequence. 

Carbonyl Compounds by Oxidation of Alcohols and Aldehydes. Salts of palladium, in particular PdCl2 in the presence of a base, catalyze the CCI4 oxidation of alcohols to aldehydes and ketones. Allylic alcohols carrying a terminal double bond are transformed to 4,4,4-trichloro ketones at 110 °C, but yield halo-hydrins at 40 °C. These can be transformed to the corresponding trichloro ketones under catalysis of palladium acetate (eq 56). The latter transformation could be useful for the formation of ketones from internal alkenes provided the halohydrin formation is regioselective. 

Oxidation of primary vinyl methyl ethers yields a,p-unsaturated aldehydes. The method has been applied to a transformation of saturated aldehydes to one-carbon homologated unsaturated aldehydes (eq 61) by a Wittig reaction and subsequent palladium acetate-mediated oxidation. The oxidations, which were carried out in NaHC03-containing aqueous acetonitrile, yielded 50-96% of the unsaturated aldehydes. 

Carbonylation Reactions. A three-component palladium-catalyzed amidocarbonylation reaction provides IV-acylamino acids from aromatic and aliphatic aldehydes or acetals with amides under elevated CO pressure (60 bar) in the presence of PdBr2, PPhs, LiBr, an acid additive (typically H2SO4), and iV-methyl-2-pyrrolidone. Mechanistically, the palladium-catalyzed amidocarbonylation reaction is proposed to proceed through the in situ formation of an a-haloamide and Pd(0) species, which can undergo oxidative addition, followed by CO insertion, and lastly hydrolysis of the acyl palladium complex to afford the product and regenerate the catalyst (eq 45). 

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