Palladium catalysts reductions with

These substances, like most compounds with peroxide (O—O) bonds, may explode violently and unpredictably. Therefore ozonizations must be carried out with appropriate caution. The general importance of these reactions derives not from the ozonides, which usually are not isolated, but from their subsequent products. The ozonides can be converted by hydrolysis with water and reduction, with hydrogen (palladium catalyst) or with zinc and acid, to carbonyl compounds that can be isolated and identified. For example, 2-butene... 

Dihydroindoles are produced in good yield from 1-phenylsulfonylindoles by reduction with sodium cyanobor-ohydride in TFA at OC (e.g. Scheme 74). If acyl groups are present at C(2) or C(3) in the substrate, they are reduced to alkyl groups. Indole itself is also reduced to 2,3-dihydroindole by sodium cyanoborohydride and acetic acid or triethylamineborane and hydrochloric acid. An alternative method for preparing indolines involves treatment of indoles with formic acid (or a mixture of formic acid and ammonium formate) and a palladium catalyst. Reduction of the heterocyclic ring under acidic conditions must involve initial -protonation followed by reaction with hydride. 

A detailed study of the hydrogenation of valylene (2-methyl-but-l-ene-3-yne) and isoprene has shown that palladium catalysts poisoned with lead can give highly chemoselective reductions. ... 

The concept of CPTC has been applied in a large number of catalytic reactions such as reduction of allyl chlorides with HCOONa, carbonylation of aryl and allyl halides, allylation of aldehydes, cyanation of aryl halides etc. For example, Okano et al. reduced l-chloro-2-nonene to afford 1-nonene and 2-nonene (Equation 17) with selectivities of 82% and 17%, respectively using palladium catalysts modified with the water soluble polyether phosphine 76 (Table 4 n=0, x=l, m=3, R=Me) in an heptane/H20 (8/2) two phase system according to CPTC concept. 

This reaction is favored by moderate temperatures (100—150°C), low pressures, and acidic solvents. High activity catalysts such as 5—10 wt % palladium on activated carbon or barium sulfate, high activity Raney nickel, or copper chromite (nonpromoted or promoted with barium) can be used. Palladium catalysts are recommended for the reduction of aromatic aldehydes, such as that of benzaldehyde to toluene. 

Hydrogenation of cinnamaldehyde has been studied extensively since selectivity has often been an issue. Under mild conditions the carbonyl group is reduced giving cinnamyl alcohol, whereas at elevated temperatures complete reduction to 3-phenylpropanol [122-97 ] results. It is possible to saturate the double bond without concomitant reduction of the carbonyl group through selective hydrogenation with a ferrous chloride-activated palladium catalyst (30), thereby producing 3-phenylpropanol [104-53-0]. 

Reduction of isoindoles with dissolving metals or catalytically occurs in the pyrrole ring. Reduction of indolizine with hydrogen and a platinum catalyst gives an octahydro derivative. With a palladium catalyst in neutral solution, reduction occurs in the pyridine ring but in the presence of acid, reduction occurs in the five-membered ring (Scheme 38). Reductive metallation of 1,3-diphenylisobenzofuran results in stereoselective formation of the cw-1,3-dihydro derivative (Scheme 39) (80JOC3982). 

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). 

The reduction does not proceed smoothly at room temperature with the palladium catalyst. Raney nickel may be used as a catalyst with ethanol containing potassium hydroxide at room temperature, but about 15 hours are required for reduction. 

Palladium catalysts have been prepared by fusion of palladium chloride in sodium nitrate to give palladium oxide by reduction of palladium salts by alkaline formaldehyde or sodium formate, by hydrazine and by the reduction of palladium salts with hydrogen.The metal has been prepared in the form of palladium black, and in colloidal form in water containing a protective material, as well as upon supports. The supports commonly used are asbestos, barium carbonate, ... 

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into lTans-l,2-diols by acid-catalyzed epoxide hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with 0s04. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. 

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