Aldehydes to unsaturated alcohols

Cobalt boride has been used for reducing unsaturated aldehydes to unsaturated alcohols improved results are obtained by addition of ferric chloride or chromium chloride (6S). It is a low-activity catalyst. 

One of the major challenges is the selective hydrogenation of unsaturated aldehydes to unsaturated alcohols which attracted much interest [182]. The highly selective hydrogenation of 3-methyl-2-butenal (prenal) to 3-methyl-2-... 

Complex hydrides can be used for the selective reduction of the carbonyl group although some of them, especially lithium aluminum hydride, may reduce the a, -conjugated double bond as well. Crotonaldehyde was converted to crotyl alcohol by reduction with lithium aluminum hydride [55], magnesium aluminum hydride [577], lithium borohydride [750], sodium boro-hydride [751], sodium trimethoxyborohydride [99], diphenylstarmane [114] and 9-borabicyclo[3,3,l]nonane [764]. A dependable way to convert a, -un-saturated aldehydes to unsaturated alcohols is the Meerwein-Ponndorf reduction [765]. 

On the basis of the above conclusions, the selective hydrogenation of a,/J-unsaturated aldehydes to unsaturated alcohols can be achieved by taking into account the following considerations and factors ... 

One of the most interesting applications of these catalytic systems is the regioselective reduction of a, -unsaturated aldehydes to unsaturated alcohols or saturated aldehydes [18,19]. For example, 3-methyl-2-buten-l-al or prenal was selectively reduced to prenol with a selectivity up to 97% using ruthenium complexes associated with tppts in a mixture of water/toluene at 35 °C and 20 bars hydrogen [Eq. (1)] conversely, the saturated aldehyde was obtained with a selectivity up to 90% using RhCl(tppts)3 as the catalyst at 80 °C and 20 bars hydrogen. The same selectivities were observed for (Ej-cinnamaldehyde,2-buta-nal and citral. 

Reduced osmium on carbon is an excellent catalyst for selective hydrogenation of aj3-unsaturated aldehydes to unsaturated alcohols.1 Cinnamaldehyde — cinnamyl alcohol (95% yield). Reduced rates are observed with alumina as the support. This selective reduction is not applicable to a,/3-unsaturated ketones thus hydrogenation of mesityl oxide afforded methyl isobutyl ketone. 

The selective hydrogenation of unsaturated aldehydes to unsaturated alcohols is an important reaction for the production of line chemicals. Even though the selective formation of imsaturated alcohols has been viewed as a difllcult problem, recent investigations have shown that the selectivity of a metal catalyst can be very much improved by a) varying the metal particle size... 

Re, Os (Pt, Ru) are used for the hydrogenation of unsaturated aldehydes to unsaturated alcohols... 

Chen JX, Daeuble JF, Brestensky DM, Stryker JM (2000) Highly chemoselective catalytic hydrogenation of unsaturated ketones and aldehydes to unsaturated alcohols using phosphine-... 

Joo, F. Benyei, A. (1989) Biphasic reduction of unsaturated aldehydes to unsaturated alcohols by ruthenium complex-catalysed hydrogen transfer, J. Organomet. Chem., 363, C19-21. 

The unusual selective hydrogenation of a, )8-unsaturated aldehydes to unsaturated alcohols has also been accomplished using [RhCl(CO)2]2 in the presence of tertiary amines under oxo-conditions. Willdnson s catalyst reduces the alkene double bond under the same conditions [25]. 

Ru/tppms catalysts exhibited excellent yields (98%) in the transfer hydrogenation of unsaturated aldehydes such as cinnamaldehyde or crotonaldehyde, to the corresponding unsaturated alcohols under mild reaction conditions (30-80°C), with HCOONa in an aqueous/organic two phase system. Similarly, ruthenium modified with the water soluble, air stable phosphine 100 (pta Table 5) is an effective catalyst for the chemoselective transfer hydrogenation of a,P-unsaturated aldehydes to unsaturated alcohols using formate in an aqueous/ organic two phase system. In contrast, Rh/pta afforded the cor-... 

The WGSR may be used to effect selective reductions. For example, [Mn2(CO)8(PBu3)2] catalyzes the reduction of anthracene by CO + D2O to give 9,10-dideuterioanthracene similarly with CO + H2O, [Fe(CO)5] + Et3N catalyzes reduction of PhCH=NPh to PhCH2NHPh and [Rh6(CO)i6] + Mc2NCH2CH2NMe2 catalyzes the reduction of unsaturated aldehydes to unsaturated alcohols. ... 

The selective hydrogenation of a,P-unsaturated aldehydes to unsaturated alcohol is an important reaction in the production of many pharmaceutical, agrochemical, and fragrance compounds. The hydrogenation of the C=C bond is thermodynamically more favorable than C=0 hydrogenation, and low yields of the desired product are obtained with conventional hydrogenation catalysts. 

Scheme 6.8 Selective hydrogenation of a,P-unsaturated aldehydes to unsaturated alcohols in water.

Zhu et al. [69] have studied the catalytic performance of thiolate-protected Au25(SR)jg dusters for the selective hydrogenation of different a,p-unsaturated ketones and aldehydes to unsaturated alcohols (U As) (Table 11.2). A100% sdectivity was achieved for different reactant substrates except acrolein, for which a selectivity of 91% allylic alcohol was obtained. The core-shell structure of the Au25(SR)jg (Aujj core/AUi2 shell) and their unique electronic properties (electron-rich Auj,... 

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