Reduction of multiple bonds

Solutions of Moiseev s giant Pd colloids [49,161-166] were shown to catalyze a number of reactions in the quasi homogeneous phase, namely oxidative ace-toxylation reactions [162], the oxidative carbonylation of phenol to diphenyl carbonate [166], the hydrogen-transfer reduction of multiple bonds by formic acid [387], the... 

Moiseev, I.I., Tsirkov, G.A., Gekhman, A.E., and Vargaftik, M.N., Facile hydrogen- transfer reduction of multiple bonds by formic acid catalysed with a Pd-561 giant cluster, Mendeleev Commun., 7,1-3,1997. 

Of the various catalysts used for the reduction of multiple bonds, Raney nickel is very effective. 

Reduction of multiple bonds with samarium diiodide has been reviewed. Chemo-and stereo-selective reduction of various compounds such as conjugated alkenes, c/,/3-unsaturated carboxylic acids, activated alkynes, carbonyl, azides, nitriles, and nitro compounds, under mild conditions, has been discussed. Recent developments in the use of samarium metal in this field have also been discussed.381... 

Stereochemical studies on the reduction of C==C and by diimide have shown that the transfer of hydrogens from diimide occurs in a completely syn manner. The reduction of (4) and (5) with dideute-riodiimide, generated by the deuterolysis of dipotassium azodiformate, resulted in the formation of the meso- and ( )-reduction products (6) and (7) in at least 97% stereospecificity (the lower limit of detectability with IR spectral analysis). The reduction of diphenylacetylene (8) produces only c/ s-stilbene (9) as an intermediate reduction product. It was considered that the reduction of multiple bonds by diimide occurred as a synchronous transport of a pair of hydrogens to a single face of the rr-system via a transition state represented as (10). ... 

But asymmetric applications remain arguably the area to further develop since with notable exceptions, the level of chiral induction for these reactions remains disappointing. Hopefully the known studies will lead to new strategies for the development of more reactive and selective catalysts in the reduction of multiple bonds. 

In Part 2 of this book, we shall be directly concerned with organic reactions and their mechanisms. The reactions have been classified into 10 chapters, based primarily on reaction type substitutions, additions to multiple bonds, eliminations, rearrangements, and oxidation-reduction reactions. Five chapters are devoted to substitutions these are classified on the basis of mechanism as well as substrate. Chapters 10 and 13 include nucleophilic substitutions at aliphatic and aromatic substrates, respectively, Chapters 12 and 11 deal with electrophilic substitutions at aliphatic and aromatic substrates, respectively. All free-radical substitutions are discussed in Chapter 14. Additions to multiple bonds are classified not according to mechanism, but according to the type of multiple bond. Additions to carbon-carbon multiple bonds are dealt with in Chapter 15 additions to other multiple bonds in Chapter 16. One chapter is devoted to each of the three remaining reaction types Chapter 17, eliminations Chapter 18, rearrangements Chapter 19, oxidation-reduction reactions. This last chapter covers only those oxidation-reduction reactions that could not be conveniently treated in any of the other categories (except for oxidative eliminations). 

In the case of the anion-radical of benzophenone, the effect of an added electron is not very specific It results in weakening of multiple bonds and strengthening of single bonds. Such an effect is usual for all organic anion-radicals. One-electron reduction of benzophenone, a fully conjugated ketone, yields a ketyl and results in the general bond loosening (Scheme 2.38). 

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. 

Hydrogenation of multiple bonds, like C=C, C=0, C=N, C=S, N=N, C=C, N=N, and bonds in NO and NO2, bonds in quinones and quinone-like structures and in aromatic rings are often followed in protic media. Under such conditions such reductions often involve a proton transfer, either preceding or following the electron transfer. 

Reduction or disproportionation of univalent group 13 compounds generally resnlts in the formation of multiple-bonded species, clusters, and metals (eqnation 3). Such reactivity has been exploited for the prodnction of indium nanoparticles (y = 0) by the solvothermal decomposition of Cpln. Similarly, the thermal decomposition of many RM compounds (M = Al, Ga, In) results in the elimination of a portion of the substituents and produces metal-rich group 13 clusters of various sizes the clusters obtained are thonght to be intermediates on the pathway to the formation of bnlk metal. ... 

Other typical reactions of acidic hydrocarbons with alkali metals are given in Table 1. Example 4 (Table 1) shows that, in addition to hydrogenation of multiple bonds, reductive cleavage may be a complicating side reaction. In the reaction of triphenylmeth-ane this side reaction may be eliminated by addition of butadiene which, as its radical anion, acts as proton acceptor. 

The O transitions may take place in the far ultraviolet, which is generally not recorded in spectrophotometers. Other transitions occur in the near ultraviolet and visible regions. The n —> 7C transitions are characterized by high intensity which varies depending on the number and kind of multiple bonds in the molecule. An increase in the number of conjugated bonds results in a reduction of the distance between the k and 7t levels, an increase in the probability of transition, and increase of intensity of the spectrum recorded. 

The reduction of multiple C—C bonds with excess in a suitable solvent in the presence of a metal catalyst can achieve controlled transformations with little experimentation. This addition proceeds easily and is widely used in organic synthesis. 

The most important processes for addition of hydrogen to the ethylenic bond and to aromatic and heterocyclic systems comprise reduction by nonnoble metals in suitable solvents. All other reducing agents, such as tin(n) chloride, hydrogen iodide, and even complex metal hydrides, are much less important for reduction of multiple C—C bonds. 

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