Unsaturated esters, hydrogenation chemoselective

Hydroformylation of a range of 1,1-di- and 1,1,2-trisubstituted unsatur-ated esters yields quaternary aldehydes (Table 1, entries 1-8). Hence, the regiochemistry-directing influence of the electron-withdrawing ester function overcompensates Keuleman s rifle. Furthermore, hydroformylation of 1,2-disubstituted unsaturated esters occurred with high a-selectivity and chemoselectivity (Table 1, entries 9 and 10). As a side reaction hydrogenation of the alkene has been observed [41]. 

DIBAL was used for the conjugate reduction to produce aluminum enolates in the presence of MeCu catalyst [39]. Unlike strong bases fhat readily deprotonate the a-hydrogen of carbonyl compounds, fhis mefhod tolerates a ketone carbonyl and its a hydrogen, and was fhus chemoselective as well as quantitatively reducing fhe a,/ -unsaturated ester (Scheme 6.19). 

Recently, it has been shown by Xiao et al. that cyclometalated iridium(III) complexes can be switched on by controlling the solution pH to function as catalysts for the TH of carbonyl compounds in water using formate as the hydrogen source. Substituted benzophenones as well as alkyl aryl and dialkyl ketones were reduced in high yields (79-99 %) using 0.05 mol% of catalyst 202 (Fig. 61) [197]. Catalysts 203 and 204 were examined in the chemoselective TH of various a-substimted ketones, keto esters, and a,p-unsaturated aldehydes in water [198]. It was clearly shown that the pH of the reaction solution plays the crucial role, and pH... 

The hydrogenation of a,j0-unsaturated aldehydes to allylic alcohols in quantitative yields in j -PrOH is catalysed by [FeF(P(PhPPh2)3)][BF4] in the presence of trifluo-roacetic acid. The catalyst could reduce a broad range of aromatic and aliphatic aldehydes in the presence of other reducible moieties (ketones, olefins, esters, etc.) with high chemoselectivity. Computational calculations and detection of the hydride species [FeH(H2)(P(PhPPh2)3)]", in situ, suggest a catalytic cycle. ... 

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