Reduction of double bonds

Triethylammonium formate is another reducing agent for q, /3-unsaturated carbonyl compounds. Pd on carbon is better catalyst than Pd-phosphine complex, and citral (49) is reduced to citronellal (50) smoothly[55]. However, the trisubstituted butenolide 60 is reduced to the saturated lactone with potassium formate using Pd(OAc)2. Triethylammonium formate is not effective. Enones are also reduced with potassium formate[56]. Sodium hypophosphite (61) is used for the reduction of double bonds catalyzed by Pd on charcoal[57]. 

There are ample precedents for reductions of double bonds in conjugated enones with lithium in deuterioammonia (see section V-C). Examples of the reduction of saturated ketones in deuterated media appear only as side reactions (over reductions) during the above mentioned conversions. For experimental details, therefore, one should consult the literature for the analogous reductions in protic medium (see also chapter 1). The use of deuterioammonia is essential for labeling purposes since by using liquid ammonia and methanol-OD the resulting alcohol contains no deuterium. For the preparation of deuterioammonia see section IX-D. 

The study of optical isomers has shown a similar development. First it was shown that the reduction potentials of several meso and racemic isomers were different (Elving et al., 1965 Feokstistov, 1968 Zavada et al., 1963) and later, studies have been made of the ratio of dljmeso compound isolated from electrolyses which form products capable of showing optical activity. Thus the conformation of the products from the pinacolization of ketones, the reduction of double bonds, the reduction of onium ions and the oxidation of carboxylic acids have been reported by several workers (reviewed by Feokstistov, 1968). Unfortunately, in many of these studies the electrolysis conditions were not controlled and it is therefore too early to draw definite conclusions about the stereochemistry of electrode processes and the possibilities for asymmetric syntheses. 

A few remarkable, but rather uncommon, transfer hydrogenations also deserve mention within the context of this chapter namely, the reduction of alkynes to alkenes using a chromium catalyst, and the reduction of double bonds using diimines. 

One very fast and reliable method for the reduction of double bonds is that of transfer hydrogenation with diimine (Scheme 20.30). Under the influence of traces of copper ion and oxygen from air, hydrazine is rapidly transformed into diimine. This compound is able to hydrogenate double bonds with great success under the formation of nitrogen [120],... 

Hydrogenation of double and triple bonds has already been discussed. If the compound contains reducible functional groups, they may also be reduced but selective reduction of double bonds has been possible under suitable conditions. 

Reactive donors can be generated ca-thodically by reductive cleavage of hahdes to carbanions or by reduction of double bonds to radical anions. Using these methods, two acceptors can be dimerized in one step by reductive Umpolung , for example, two molecules of acrylonitrile to adipodini-trile - a reaction, which normally needs two or more steps. 

Dihydroxy-4-butyrolactone, 46, 24 Diimide, in reduction of double bonds,... 

In addition to the described reduction of double bonds conjugated to a carbonyl group, sodium hydrogen telluride and phenyltellurol reduce double (and triple) bonds conjugated to aromatic systems. " ... 

Metabolism. Eicosanoids are inactivated within a period of seconds to minutes. This takes place by enzymatic reduction of double bonds and dehydrogenation of hydroxyl groups. As a result of this rapid degradation, their range is very limited. 

Saccharomyces cerevisiae (Baker Yeast) are micro organisms and are used for the reduction of carbonyl group to hydroxyl group and for reduction of double bond. 

The reduction of double bonds using chiral phosphine ligands as the precursors for the appropriate catalysts is a widely used strategy in the asymmetric synthesis of... 

The reduction of double bond-containing functionalities, especially alkenes and carbonyl compounds, is an important methodology used in synthetic elaboration. In this section the stereocontrolled reduction of aldehydes, ketones and C=N-containing compounds and the catalytic hydrogenation of alkenes are covered, among other reductions. The emphasis here is placed on stereocontrolled reactions. 

Reduction of acyl chlorides to aldehydes,13 Tri-n-butyltin hydride reduces acyl chlorides to a mixture of aldehydes and esters. In the presence of a soluble Pd catalyst usually Pd[P(C6H5)3]4, only aldehydes obtain. This reduction is very general, and yields are usually > 80%. Reduction of double bonds is a minor competing reaction with a, / -unsaturatcd substrates (< 5% reduction). Of other reducible groups, only an allylic bromide group competes with the COC1 group. 

Introduction of a double bond increases the rigidity of the structure and in some cases the possibility of E and Z isomers. The reduction of double bonds makes the structure more flexible. 

The production of a,m-diesters from fatty esters can be realized via their SM as already explained, but it can also be performed by CM with methyl acrylate. The bulk CM of several unsaturated fatty acid methyl esters containing double bonds in different positions with methyl acrylate was studied by Rybak and Meier (Scheme 6) [43], C4 and C5 displayed very good activities with high conversions and CM selectivities. Among them, C5 showed the best performance for both methyl oleate (97% conversion, 92% selectivity, with 0.2 mol%) and methyl 10-undecenoate (99% conversion, 99% selectivity, with 0.1 mol%). The same conditions were successfully applied to methyl erucate and methyl petroselinate. The reaction conditions were further optimized, also considering the effect of 1,4-benzoquinone as additive for the reduction of double-bond isomerization [39], The CM of methyl 10-undecenoate and methyl acrylate worked with full conversions and high selectivity if five- to tenfold excess of methyl acrylate is used. Furthermore, using a 1 1 ratio between both reactants led, after optimization of the reaction... 

Another approach for the reduction of double bonds is to use hydride reagents H-Y, such as HBR2 or HSiR.3. Once the adduct has been formed, the task is to replace Y by H. This is straightforward when Y is fixed to an oxygen or nitrogen, as acidic hydrolysis will cleave the O-Y or N-Y bond. This is illustrated in Scheme 11.2 for the reduction of ketones and conjugated ketones. 

The advantages of 10 % Pd/C include the short reaction time and the ease with which the catalyst can be separated from the product after the reaction is completed. The disadvantage is that 10 % Pd/C catalyzes the reduction of double bonds under the reaction conditions, therefore it is not compatible with substrates containing carbon-carbon multiple bonds. 

Under appropriate experimental conditions, hydrogen telluride, phenyl tellurol, and sodium hydrogen telluride perform the selective reduction of double bonds of a,/3-unsaturated carbonyl systems.89 90 This reaction with a,j3-unsaturated ketones complements the cerium trichloride/sodium borohydride method, which reduces the carbonyl group, keeping the carbon-carbon double bond intact92 (Scheme 18). 

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