Acetophenone derivative reduction

In a similar vein, the keto bridge in 5 can be replaced by oxygen with retention of activity. Reduction of acetophenone derivative 19 by means of sodium borohydride leads to the corresponding alcohol (20). Reaction with phosphorus tribromide with cyanide gives... 

Nickel boride prepared from Nil2 and two equivalents of LiBH4 [42] was utilized as an oxazaborolidine catalyst support (Scheme 4) [43]. Reaction of nickel boride with 0.1 equivalents of chiral amino alcohol in THF at room temperature gave the anchored catalyst 6, which produced chiral alcohols in optical yields of up to 95%, and which furthermore showed higher activity as regards the reduction of acetophenone derivatives than that of the corresponding homogene-... 

If chelation to a neigbouring group is possible, the use of HMPA is often not required for reduction of the carbonyl and reactions can be carried out under mild conditions. To examine the impact of chelation, Flowers studied the rate of reduction of 2-butanone, methyl acetoacetate and /V,/V-dimethylacetoace-tamide by Sml2.20 Reduction of the (1-keto ester or amide was several orders of magnitude faster than that of the unsubstituted ketone, which is consistent with chelation playing a major role. Further rate and mechanistic studies on the reduction of acetophenone and a series of 2 - and 4 -substituted acetophenone derivatives showed that both chelation and coordination provide highly... 

Reduction of acetophenone derivatives gives intermediates which are suitable for the preparation of ENA-713 (Novartis), an acetylcholinesterase inhibitor... 

In 2009, Xiao employed a half sandwich Cp lr(l 11) complex with different chiral monosulfonated OPEN ligands (Figure 7.2), earlier developed for imine reduction by the same group, in combination with a BINOL based chiral phosphate counteranion (TRIP anion), to reductively aminate 24 acetophenone derivatives (1.2 equiv) with p anisidine (limiting reagent) under the conditions of 1.0 mol% of the indicated Ir catalyst (Table 7.1), 5 bar (73 psi) H2, toluene, 35 °C, and 15 24h [14]. 

Table 7.1 Ee values for Ir based reductive amination of acetophenone derivatives with p anisidine.

For example, the effect of cultivation time and different carbon sources on the enantioselectivity of the reduction of sulcatone by some anaerobic bacteria has been investigated [8 if Another example is the investigation on the effect of the medium concentrations for cultivation of Geotrichum candidum IFO 4597 on the enantioselectivity of the reduction of acetophenone derivatives. The yield of l -alcohol (the minor enantiomer) increased with the medium concentration therefore, the medium concentration was kept low, optimally to produce the S-enantiomer[82]. The effect of the aeration during cultivation on the enantioselectivity of bakers yeast production of 3-hydroxyesters has also been reported 86 Inducers such as a substrate analog may also induce the desired enzyme to improve the enantioselectivity. 

Assuming that the enantioselection mechanism for artificial transfer hydroge-nases using biotinylated d -piano-stool complexes should be similar to the homogeneous systems, we initially focused on the reduction of prochiral acetophenone derivatives [57-59]. Systematic variation of the pH revealed that these systems perform best at pH 6.25. As the pH rises during catalysis, we used a mixed buffer consisting of a sodium formate and boric acid mixture. Addition of MOPS further contributed to stabilization of the pH and improved the selectivity of the system. 

Table 4 Molecular Imprinting Effect in the Reduction of Acetophenone derivatives by Using Rh Catalyst...

The effects of both template and amine ligands were examined for the reduction of acetophenone derivatives with the rhodium catalysts (Table 4). The reduction of propiophenone using P-8a, b was also examined to eliminate the possibility of the template leaching to distort the product analysis (entry 7). The enantioselectivity was the highest reported of the series, although the results were still unremarkable when compared to the homogeneous examples. 

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