Raney nickel Subject

Isothiazoles are reductively desulfurized by Raney nickel, e.g. as in Scheme 31 (72AHC(l4)l). 1,2,5-Thiadiazoles are subject to reductive cleavage by zinc in acid, sodium in alcohol, or Raney nickel, e.g. Scheme 32 (68AHC(9)107). 

Chrzanowska and Rozwadowska (60) performed a total synthesis of ( )-43, using amine 49 and the thioacetal of methoxycarbonylpiperonal (26) as substrates (Scheme 13). These two synthons were joined together under the influence of LDA, and the resulting addition product 50 was subjected to reductive desulfurization with Raney nickel to give racemic peshawarine (43). 

We chose the microwave-enhanced Raney Nickel catalyzed hydrogen isotope exchange of indole and N-methylindole as our substrates and D20, CD3COCD3, CD3OD and CDC13 as the solvents. The thermal reaction had already been the subject of a recent study [44], The microwave-enhanced method was some 500-fold faster than the corresponding thermal reaction (at 40 °C). Furthermore the pattern of labeling (Scheme 13.3) varied with the choice of solvent. Thus in the case of indole it-... 

Compound 230 is subjected to desulfuration with dilute nitric acid to give product 89 in 60% yield (Scheme 16) the same product is obtained when compound is treated with Raney-nickel <1998IJC(B)921>. 

Improved synthesis by this method has been achieved in order to obtain solenopsin A (Id) more stereoselectively 388). A cis and trans mixture of pyridine derivative 158, obtained from 156 by the Wittig reaction, was reduced by Raney nickel catalyst in the presence of PtOj to yield the m-piperidine (Ic). The Af-nitroso derivative 159, obtained from Ic by treatment with isoamyl nitrite, was treated with potassium rert-butoxide and then subjected to hydrogenolysis over Raney nickel to give a mixture of ( )-solenopsin A (Id, 1 part) and its isomer (Ic, 1 part) (Scheme 3). 

The Merck process group subsequently published a more detailed route amenable towards multikilogram scales (Blacklock et al., 1988). This synthesis begins with treatment of alanine with phosgene to produce A-carboxyanhydride (NCA) 16 (Scheme 10.3). Under basic aqueous conditions this anhydride is coupled with proline to produce, upon acidic work-up, the dipeptide alanyl-proline (14). Enalapril is then prepared in one synthetic step by a diastereoselective reductive amination between ethyl-2— oxo-4-phenylbutyrate (13) and 14. This reaction was the subject of extensive optimization, and it was found that the highest diastereoselectivity was obtained by hydrogenation over Raney nickel in the presence of acetic acid (25%), KF (4.0 equiv.), and 3 A molecular sieves (17 1 dr). Enalapril is then isolated in diastereomerically pure form as its maleate salt (Huffman and Reider, 1999 Huffman et al., 2000). 

In the last few decades, the study of adsorption phenomena at nickel electrodes by a radiotracer method has been the subject of several studies (see [34-40] and literature cited therein). M ost of these studies were carried out at smooth electrodes however, in some cases, nickel powder and Raney-nickel catalysts were used. 

Pericas and Jeong demonstrated independently that sulfur-tethered substrates, when subjected to the PKR conditions, afforded the desired bicyclic products. The sulfur tether is removed cleanly by Pummerer reaction after oxidation of sulfur to sulfoxide or 1,4-addition of bisalkyl cuprate followed by hydrogenolysis of sulfide with Raney nickel. It is worth mentioning that the regioselectivity regarding the acetylene part is opposite to that of the intermolecular version (Equation (30)). 

An alternative synthesis from the Glaxo patents involves Fnedel-Crafts acylation of the 3-position of the indole intermediate 22 (Scheme 5) Reaction of hydrazine 10 with (phenylthio)acetaldehyde gave hydrazone 20, which was subjected to the Fischer indole reaction to give 3-thiophenylindole 21. It is noteworthy that this Fischer cyclization took place at room temperature because most require heat. Reductive desulfurization of 21 using Raney nickel provided indole 22. Acylation of the 3-position... 

Reactions of 4,7-phenanthroline-5,6-dione have been the subject of considerable study. It is reduced to 5,6-dihydroxy-4,7-phenanthroline by Raney nickel hydrogenation226,249 or by aromatic thiols in benzene,262 and oxidized by permanganate to 3,3 -bipyridyl-2,2 -dicarboxylic acid.263 It forms bishemiketals with alcohols226 and diepoxides with diazomethane.226 The diepoxides by reaction with hydrochloric acid form diols of type 57, R = Cl, which on oxidation with lead tetraacetate give 3,3 -bipyridyl diketones of type 58, R = Cl. Methyl ketones of type 58, R = H, are also obtained by lead(IV) acetate oxidation of the diol 57, R = H, obtained by lithium aluminum hydride reduction of 57, R = Cl. With phenyldiazomethane and diphenyldiazomethane the dione forms 1,3-dioxole derivatives,264,265 which readily hydrolyze back to the dione with concomitant formation of benzaldehyde and benzophenone, respectively. 

The loss of the catalytically active surface of Raney nickel due to recrystallization is a continuously progressing process that can be retarded to some extent in Raney-nickel anodes by dispersing oxide ceramic materials like Zr02 and Ti03 in the nickel matrix. More serious is anodic oxidation for some metals additionally accompanied by dissolution of the catalyst to which even platinum is subject but which is an even more serious hazard for the less noble catalysts as silver and Raney nickel. 

A solution of methyl 3,6-dichloro-3,6-dideoxy-p-D-allopyranoside [47] (25, 1.0 g) in ethanol (30 mL) containing W-4 Raney nickel catalyst [27,58] (20 mL ethanol slurry) and triethylamine (1.3 mL) was subjected to a hydrogen pressure of 45 psig for 36 h. TLC [Silica Gel G, Brinkmann 2 1 (v/v) ethyl acetate-petroleum ether (bp 60°-80°C)] showed that the starting material (R 0.42) had all reacted and revealed the presence of a new component having an Rf of 0.23. The filtered solution was concentrated to a syrup, which... 

To an acetone solution (6 ml) of the preceding (methylthio)furan (190 mg, 1 mmol) was added Raney nickel W-7 (prepared from 1 g of Raney Ni alloy) in ethanol (12 ml) and the solution was stirred for 30 min at room temperature. After filtration and washing (ethanol) of the Raney Ni, the filtrate was concentrated in vacuo. To the residue was added brine (20 ml) and the solution was extracted with ether. The combined ethereal solution was dried (MgS04), concentrated, and subjected to chromatography on Florisil (elution with pentane) to give 3-phenylfuran (42%), colourless crystals, m.p. 51-57°C. 

Secondary amines can be prepared from the primary amine and carbonyl compounds by way of the reduction of the derived Schiff bases, with or without the isolation of these intermediates. This procedure represents one aspect of the general method of reductive alkylation discussed in Section 5.16.3, p. 776. With aromatic primary amines and aromatic aldehydes the Schiff bases are usually readily isolable in the crystalline state and can then be subsequently subjected to a suitable reduction procedure, often by hydrogenation over a Raney nickel catalyst at moderate temperatures and pressures. A convenient procedure, which is illustrated in Expt 6.58, uses sodium borohydride in methanol, a reagent which owing to its selective reducing properties (Section 5.4.1, p. 519) does not affect other reducible functional groups (particularly the nitro group) which may be present in the Schiff base contrast the use of sodium borohydride in the presence of palladium-on-carbon, p. 894. 

The polar fraction of one sample from the Peru continental margin (679, E24359) was subjected to Raney Nickel desulfurization (2). The hydrocarbon fraction isolated from the desulfurized mixture was analyzed by GC-MS. 

Hydrogenation of L-sorbose, with Raney nickel catalyst to poly-hydric alcohols is the subject of a recent patent this type of reduction had previously been shown to give the expected L-iditolI 1 and D-glucitol. The open-chain acetate, keto-L-sorbose pentaacetate, on reduction192 at low pressure with platinum catalyst, gave on subsequent acetylation hexaacetyl-D-glucitol (XLIV) and hexaacetyl-L-iditol (XLV), while... 

Fig (IS) Tetralone (123) is prepared from 2,7-dim ethoxy napthalene (120) using the standard organic reactions. It is caiboxymethylated with dimethylcarbonate. The resulting compound (124) on subjection to Michael condensation yeilds tricyclic ketone (125) which on methylation followed by thioketalisation produces (128). This on desulfurisation with Raney nickel is converted to (129). 

Activation of Raney Ni by Other Metals. The promoting effect of various transition metals for Raney Ni has been the subject of a number of investigations and patents.62 Promoted Raney nickel catalysts may be prepared by two methods (1) a promoter metal is added during the preparation of the Ni-Al alloy, followed by... 

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