Raney nickel asymmetric hydrogenations with

Izumi, Y, Akabori, S., Fukawa, H., Tatumi, S., Imaida, N, Fukuda, T, Komatu, S. Asymmetric Hydrogenation with Modified Raney Nickel. Proc. Third Intern. Congr. Catalysis. Volume II, p. 1364. Amsterdam North Holland Publ. Comp. 1965. 

Xatsumi, S., Imaida, M., Okubo, K. Asymmetric Hydrogenation of C=0 Double Bonds with Modified Raney Nickel. XIII. Modification with Peptides. Bull. Chem. Soc. Japan 43, 556 (1970). 

About 95% of all hydrogenation processes are performed using Pd/C or Raney Nickel in the heterogenous mode. " The asymmetric hydrogenation, with high enantio-selectivities is the only area where the homogenous hydrogenation can predominate. 

Izumi, Y. Imaida, M. Fukawa, H. Akabori, S. Studies on modified hydrogenation catalyst 3. Asymmetric hydrogenation with modified Raney Nickel. Bull. Chem. Soc. Jpn. 1963, 36, 155-160. 

Table 3. Asymmetric Synthesis of 2-Substituted Cyclopentanamines by Reductive Hydrogenation with Raney Nickel and Hydrogenolysis with Palladium on Charcoal26...

The efficiency of a Raney nickel catalyst for hydrogenation of carbonyl groups is much diminished if the catalyst is treated with 0.1% acetic acid or an amino acid, particularly dibasic amino acids or L-phenylalanine but the efficiency for hydrogenation of C=C double bonds remains unaffected. Thus mesityl oxide was hydrogenated to isobutyl methyl ketone selectively and in good yield but cinnamaldehyde could not be reduced in this way.161 For asymmetric hydrogenation with Raney nickel modified by optically active 2-hydroxy carboxylic acids see Tatsumi et al.162... 

Izumi, Y., Matsunaga, K., Tatsumi, S., and Imaida, M. (1968) Asymmetric hydrogenation with modified Raney nickel X., Effect of the... 

The reductive amination of ketones can be carried out under hydrogen pressure in the presence of palladium catalysts. However, if enantiopure Q -aminoketones are used, partial racemization of the intermediate a-amino imine can occur, owing to the equilibration with the corresponding enam-ine [102]. Asymmetric hydrogenation of racemic 2-amidocyclohexanones 218 with Raney nickel in ethanol gave a mixture of cis and trans 1,2-diamino cyclohexane derivatives 219 in unequal amounts, presumably because the enamines are intermediates, but with excellent enantioselectivity. The two diastereomers were easily separated and converted to the mono-protected cis- and trans- 1,2-diaminocyclohexanes 220. The receptor 221 has been also synthesized by this route [103] (Scheme 33). 

The enantioselective hydrogenation of prochiral substances bearing an activated group, such as an ester, an acid or an amide, is often an important step in the industrial synthesis of fine and pharmaceutical products. In addition to the hydrogenation of /5-ketoesters into optically pure products with Raney nickel modified by tartaric acid [117], the asymmetric reduction of a-ketoesters on heterogeneous platinum catalysts modified by cinchona alkaloids (cinchonidine and cinchonine) was reported for the first time by Orito and coworkers [118-121]. Asymmetric catalysis on solid surfaces remains a very important research area for a better mechanistic understanding of the interaction between the substrate, the modifier and the catalyst [122-125], although excellent results in terms of enantiomeric excesses (up to 97%) have been obtained in the reduction of ethyl pyruvate under optimum reaction conditions with these Pt/cinchona systems [126-128],... 

Asymmetric hydrogenations have been reported with palladium on silk 123>, palladium on modified cellulose 124> and on modified ion exchange resins 125 >. Also with Raney Nickel modified with amino adds 126> and peptides, 27>. Platinum-carbon catalysts exhibiting shape selectivity have been made by coating them with a thermosetting resin, which is carbonized. In such a way an organic molecular sieve skin is formed over the original catalyst 128>. 

In contrast to Raney nickel catalysts ( 3.4.1), heterogeneous hydrogenation catalysts based on Pt, Rh or Pd do not induce asymmetry in the presence of tartaric acid [113, 578], Platinum catalysts modified by cinchona alkaloids 3.1 and 3.2 cause asymmetric hydrogenation of the carbonyl group of a-ketoesters with a high enantiomeric excess (> 90%). From other types of ketones, the enantioselectivities are lower. 

Raney nickel, modified by free tartaric acids 2.69 (R = H) or their salts, has frequently been used as a catalyst for asymmetric hydrogenations of carbonyl compounds [578,948]. Several industrial applications have been described [578, 811, 812], Neveriess, hydrogenations of prochiral carbon-carbon double bonds in the presence of such catalysts gives disappointing results [578], The use of tartrate-modified copper catalysts in cyclopropanation of styrenes by diazoketones takes place with a modest asymmetric induction [578,936]. 

In connection with these studies, the asymmetric hydrogenation catalyzed by Raney nickel modified with dipeptide should be mentioned. In the hydrogenation of methyl acetoacetate [Eq. (5)], Izumi and his co-workers (70) found that the... 

Table 2. Asymmetric hydrogenation of methyl acetoacetate catalyzed by Raney nickel modified with dipeptide and amino acid (JO)...

Reduction of 0-methylpsychotrine by sodium and alcohol yields a mixture of emetine and isoemetine (16), whereas with hydrogen in the presence of platinum in neutral solution, or of Raney nickel (33) isoemetine is obtained. The production of two pairs of isomers, cephaeline and isocephaeline, emetine and isoemetine, by hydrogenation of the double bond, indicates the creation of a new asymmetric center, and this limits the possible position of the double bond. Furthermore, 0-methylpsychotrine on oxidation by bromine, iodine, or ferric chloride yields rubremetine (33). 

Ninomiya, T. ( 1972) Asymmetric hydrogenation of C=0 double bond with modified Raney nickel, XXII., Bull Chem. Soc. Jpn. 45, 2548 -2550. 

Ozaki, H., Tai, A., and Izumi, Y. (1974) Enantioface-differentiating (asymmetric) hydrogenation of methyl acetoacetate with modified Raney nickel, XXVIII, Chem. Lett. 935 - 938. 

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