Hydrogen-Transfer Reductions

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... 

In the same study, these authors have prepared another series of amino-sulf(ox)ide ligands based on the (Nor)ephedrine and 2-aminodiphenylethanol skeletons, bearing two chiral centres in the carbon backbone.Their application to the iridium-catalysed hydrogen-transfer reduction of acetophenone generally gave better yields, but the enantioselectivity never exceeded 65% ee (Scheme 9.4). 

Finally, the use of S/P ligands derived from (i )-binaphthol has been considered by Gladiali et al. in the asymmetric rhodium-catalysed hydrogen-transfer reduction of acetophenone performed in the presence of i-PrOH as the hydrogen donor.It was noted that racemisation occurred when the reaction time increased and consequently the corresponding alcohol was obtained in only low enantioselectivities (< 5% ee) as shown in Scheme 9.21. Similar results were more recently reported by these authors by using iridium combined with the same ligands. ... 

Another very recent development in the field of enzymatic domino reactions is a biocatalytic hydrogen-transfer reduction of halo ketones into enantiopure epoxides, which has been developed by Faber, Bornscheuer and Kroutil. Interestingly, the reaction was carried out with whole lyophilized microbial cells at pH ca. 13. Investigations using isolated enzymes were not successful, as they lost their activity under these conditions [26]. 

Poessl, T.M., Kosjek, B., Ellmer, U. et al. (2005) Non-racemic halohydrins via biocatalytic hydrogen-transfer reduction of halo-ketones and one-pot cascade reaction to enantiopure epoxides. Advanced Synthesis and Catalysis, 347 (14), 1827-1834. 

Scheme 2.7 Uncatalyzed thermal hydrogen transfer reduction of cinnamaldehyde.

The manufacture of fine chemicals and pharmaceuticals generates in the order of 25-100 times more waste than product [52], Inorganic salts account for the bulk of the waste and are most often produced by neutralization of acidic or basic solutions [53]. Salts can pollute soil and ground water, lower the pH of atmospheric moisture and they may contribute to acid dew or acid rain [6]. For cleaner production, their minimization is essential and hence our concentration on new processes, such as the etherification (discussed in Sect. 2.6.3.1) and hydrogen transfer reduction (Sect. 2.6.3.2), that avoid salt formation and the use of salts. 

Table 9.3 Hydrogen transfer reduction of ketones using Ru (II)-(/5, 3R, 4R J-i-hydroxymethyl-2-azabicyclo [2.2.1]heptane as catalyst.

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. 

Sinou and coworkers evaluated a range of enantiopure amino alcohols derived from tartaric acid for the ATH reduction of prochiral ketones. Various (2R,iR)-i-amino- and (alkylamino)-l,4-bis(benzyloxy)butan-2-ol were obtained from readily available (-I-)-diethyl tartrate. These enantiopure amino alcohols have been used with Ru(p-cymene)Cl2 or Ir(l) precursors as ligands in the hydrogen transfer reduction of various aryl alkyl ketones ee-values of up to 80% have been obtained using the ruthenium complex [93]. Using (2R,3R)-3-amino-l,4-bis(benzyloxy)butan-2-ol and (2R,3R)-3-(benzylamino)-l,4-bis(benzyloxy)butan-2-ol with [lr(cod)Cl]2 as precursor, the ATH of acetophenone resulted in a maximum yield of 72%, 30% ee, 3h, 25 °C in PrOH/KOH with the former, and 88% yield, 28% ee, 120 h with the latter. 

S. Ram u. R. E. Ehrenkaufer, Synthesis 1988,91 - -95 . .Ammonium Formate in Organic Synthesis, a Versatile Agent in Catalytic Hydrogen-Transfer Reductions". 

Several metal oxides such as A1203, CaO, Bao...[7], catalyze the hydrogen transfer reduction of simple this study we report the catalytic activity... 

Hydrogen transfer reduction of 4-hexen-3-one catalyzed by doped MgO catalysts.3... 

---