Olefin hydrogenation scheme

Catalytic metathesis has been accomplished via a tandem combination of catalytic alkane dehydrogenation, olefin metathesis and subsequent olefin hydrogenation (Scheme 12.6). Two factors are crucial for this transformation ... 

The catalytic system employing (2 - Fur)3P as ligand was applied to the coupling of methyl vinyl ketone and ethyl vinyl ketone to aromatic, aliphatic, acetylenic, and olefinic aldehydes (Scheme 23) [37]. Despite the hydrogenation conditions, alkyne and alkene moieties, as well as benzylic ether and nitro functional groups all remained intact. Furthermore, extremely high lev-... 

A number of examples involving nitrile oxide cycloadditions to cyclic cis-disubstituted olefinic dipolarophiles was presented in the first edition of this treatise, notably to cyclobutene, cyclopentene, and to 2,5-dihydrofuran derivatives (15). The more recent examples discussed here also show, that the selectivity of the cycloaddition to 1,2-cis-disubstituted cyclobutenes depends on the type of substituent group present (Table 6.8 Scheme 6.41). The differences found can be explained in terms of the nonplanarity (i. e., pyramidalization) of the double bond in the transition state (15) and steric effects. In the cycloaddition to cis-3,4-diacetyl-(197) and cis-3,4-dichlorocyclobutene (198), the syn-pyramidalization of the carbon atoms of the double bond and the more facile anti deformability of the olefinic hydrogens have been invoked to rationalize the anti selectivity observed. 

Racemic diphosphines may be resolved by using transition metal complexes that contain optically active olefinic substrates (Scheme 11) (24). When racemic CHIRAPHOS is mixed with an enantiomerically pure Ir(I) complex that has two ( —)-menthyl (Z)-a-(acetam-ido)cinnamate ligands, (S,5)-CHIRAPHOS forms the Ir complex selectively and leaves the R,R enantiomer uncomplexed in solution. Addition of 0.8 equiv of [Rh(norbomadiene)2]BF4 forms a catalyst system for the enantioselective hydrogenation of methyl (Z)-a-(acetamido)cinnamate to produce the S amino ester with 87% ee. Use of the enantiomerically pure CHIRAPHOS-Rh complex produces the hydrogenation product in 90% ee. These data indicate that, in the solution containing both (S,S)-CHIRAPHOS-Ir and (/ ,/ )-CHIRAPHOS-Rh complexes, hydrogenation is catalyzed by the Rh complex only. 

Specific dehydrogenation at the terminal positions of alkanes is a reaction that would be of high utility. The 1-alkenes obtained by such a reaction are the basis of a variety of additional products. Felkin and co-workers discovered that metal complexes are able to mediate the transfer of hydrogen from alkanes 13 to olefins 14 (Scheme 4) [17]. The specific advantages of a transition metal catalyst can be applied to the benefit of the chemoselectivity of this reaction. In a kinetically controlled process, it is predominantly primary C-H bonds that add to the metal complex. A subsequent /Miydride elimination affords the terminal alkenes... 

Scheme 16. Domino hydroformylation-Wittig olefination-hydrogenation. Reagents and conditions 1.5 Equiv.

The process scheme is not complicated and yields on olefin feed are good. The major byproduct is paraffin from olefin hydrogenation in the reactor system. However paraffin make is low. Also some olefin remains unconverted, some dimer is formed, and traces of other byproducts are made. These include acetals, esters and diols. These other losses (excluding paraffins) total less than 5%. 

Scheme 1. Classic Horiuti-Polanyi mechanism for olefin hydrogenation (2).

Sodium hydrogen telluride reacts with epoxides 41 by a Sn2 mechanism giving the respective telluroalcohols. These intermediates are easily converted into the corresponding alcohols 42 by treatment with nickel boride.97 In contrast, epoxides suffer deoxygenation when treated with alkali 0,0-dialkyl phosphorotellurolates, to give the corresponding olefins 43 (Scheme 21).98,99... 

Taking advantage of the slow hydrogenation of carbon-carbon double bonds at room temperature in the presence of platinum dioxide, it was possible to perform the ruthenium-catalyzed cross coupling reaction of electron-deficient olefins such as conjugated enones and acrylic derivatives with allyl silanes in the presence of Pt(>2 under hydrogen (Scheme 46) [99]. Prolonged... 

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