Hydrogenation of olefinic double bonds

Reduction. Successful asymmetric hydrogenations of olefin double bonds mediated by chiral phosphines have been reported (16) and the factors crucial for effective asymmetric induction in related systems have been discussed (17, 18). These reductions require functionality proximate to the double bond for any degree of success. 

Metal catalysed reactions are differentiated introducing the concept of facile and demanding reactions. In principle a single atom should be adequate for a facile (structure insensitive) reaction, while an ensemble of surface atoms is required to form a catalytic site adequate for demanding (structure sensitive) reactions. Consequently, there are reactions, which requires more than one species to form multiplets " or ensembles. In other words, some reactions depend on the surface geometry e.g. hydrogenolysis of hydrocarbons), while other may not e.g. hydrogenation of olefinic double bond). 

Metal deposits which are useful for preparative purposes may be obtained by thermal decomposition of suitable volatile metal compounds (hydrides, carbonyls) on hot surfaces. For Instance, decomposition of Ni(CO)4 on Pyrex glass wool at 150°C produces a deposit of very finely divided nickel, which is an excellent catalyst for gas-phase hydrogenation of olefinic double bonds [4]. 

For the hydrogenation of olefinic double bonds, both the alkene and hydrogen must be activated. Various mechanisms have been proposed for alkene hydrogenation, one of which we will discuss in more detail here (Scheme 5-1) [32],... 

Z. Ogumi, K. Nishio, Z. Yoshizawa, Application of the SPE method to organic electrochemistry - II. Electrochemical hydrogenation of olefinic double bonds, Electrochim. Acta 1981, 26, 1779-1782. 

Synthesis of the title compound is representative of a number of syntheses of nonaromatic nitrogen heterocycles via Pd(Ill-catalyzed amination of olefins. These tosylated enamines are not readily available by standard synthetic methods, and show potential for further functionalization of the heterocycle. The saturated amine can be synthesized from the title compound by hydrogenation of the double bond followed by photolytic deprotection. ... 

While the foregoing concepts have been utilized to rationalize the product distribution obtained on hydrogenation of a number of monocyclic olefins, it should be noted that the effect of pressure on the stereochemistry of hydrogenation of steroidal double bonds has not been critically evaluated. 

Most problems concerned with olefin hydrogenation involve the competitive hydrogenation of a double bond in the presence of another double bond or other function. There Is usually a way of achieving the desired selectivity. 

The etherified starch was further transformed by hydrogenation of the double bonds to yield the corresponding linear octyl groups using [RhCl(TPPTS)3] catalyst soluble in EtOH-H20 mixtures. Complete hydrogenation was obtained at 40 °C under 30 bar of H2 after 12 h using 0.8-wt.% Rh-catalyst [84]. Other catalytic transformations such as double bond oxidation and olefin metathesis could possibly be used to prepare other modified starches for various applications. 

Metathesis reactions are now widely used in natural product synthesis. Novel retrosynthetic analyses were developed because a carbon-carbon single bond can be formed after hydrogenation of a double bond constructed by metathesis. Although many types of metathesis are now known, the reaction is classified by olefin, enyne, and alkyne metatheses in this chapter. 

An excellent review of the problems of the enantioselective heterocatalytic hydrogenation of prochiral double bonds, covering the literature up to 1970, has been compiled by Izumi57). Raney nickel catalysts modified with chiral amino acids or dipeptides gave only very moderate enantiomeric excesses of between 0 and 10% in the hydrogenation of olefins, carbonyl compounds or oximes 57). Only Raney nickel modified with (S)-tyrosine furnished a higher enantiomeric excess in the products58). 

In general the rates of hydrogenation of steroidal double bonds can be roughly classified as follows (a) readily hydrogenated A1, A2, A3, A4, A6, A14, A15 A14 16 diene, A16, A17(20), A20 and 19-vinyl (b) moderately difficult A5 > A22 and (c) difficult to hydrogenate A8 > A9(11) > A7 > A8(14). The data for the hydrogenation of A7-steroids is obscurred by the fact that this olefin is isomerized readily to the 8(14) position. Double bond isomerization does not occur with A7-9/ -steroids.18,23,39,54... 

In neutral medium A16-, A17(20)-, and A20-olefins are hydrogenated over palladium in preference to the double bonds of A4-3-ketones.67 The double bonds of A4-3-ketones and A16-20-ketones are reduced in preference to A5-,93 A7-48 155 and A9(I -olefins.2 169 The double bond of a A14-16-ketone is saturated before a 5-ene.70,163 In basic medium the carbonyl conjugated double bond is preferentially saturated in all cases92 presumably because of the strong adsorption of the enolate anion (see section II-C). Debromination (9a-bromo 11-ketone) occurs before saturation of the A4-3-keto double bond14 over Raney nickel but hydrogenation of benzyl ethers takes place concurrently with the hydrogenation of this double bond over palladium in neutral medium.96... 

Isomerization. Double Bond. The isomerization of olefinic double bonds frequently accompanies hydrogenations (47,48). In addition, the reaction is promoted by such complexes as RhCl3 (49), (< 3P2RuC12 (50), (4>CN)PdCl2 (51), and [(C2H4)PtCl]2 (52). 

With 2-propanol as solvent, the tendency to hydrogenate the olefinic double bond in the 6 position is reduced, thus very good yields in citronellol were observed in tnis solvent. The formation of the two indesiraole products 3,7dii,iethyloctanal and 3,7 dimethyloctanol being almost annihilated. 

Catalytic hydrogenation of the double bond of the allylic alcohol with either Pd/C or an iridium catalyst would lead to reduction also of the terminal olefinic linkage. 

U. Kazmaier, J. M. Brown, A. Pfaltz, P. K. Matzinger, H. G. W. Leuenberger, Formation of C-H Bonds by Reduction of Olefinic Double Bonds Hydrogenation, in Methoden Org. Chem. (Houben-Weyl) 4th ed. 1952-, Stereoselective Synthesis (G. Helmchen, R. W. Hoffmann, J. Mulzer, E. Schaumann, Eds.), Vol. E21d, 4239, Georg Thieme Verlag, Stuttgart, 1995. 

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