Aldehydes reductive reactions

Which of the following is die producL of an aldehyde reduction reaction ... 

Strategies for Transient Kinetic Measurements. To simplify the kinetic behavior of the system, two sets of experimental conditions were selected. In the direction of aldehyde reduction, reaction was carried out under conditions where both aldehyde and NADH were present in large excess relative to the initial enzyme concentration, [E]o. To achieve the limitation of reaction to a single turnover of sites, the reaction was carried out in the presence of the potent inhibitor pyrazole (Pyr). Pyrazole reacts rapidly and quasi-irreversibly to trap enzyme-bound NAD product in the form of a covalent adduct at the 4-position of the nicotinamide ring [Eq. (2)]. 

Reduction Reactions. Aldehydes can be hydrogenated to the corresponding alcohol using a heterogeneous catalyst, for example... 

In certain cases, alkanolamines function as reduciag agents. For example, monoethanolamine reduces anthraquiaone to anthranols, acetone to 2-propanol, and azobenzene to aniline (17). The reduction reaction depends on the decomposition of the alkan olamine iato ammonia and an aldehyde. Sinulady, diethan olamine converts o-chloronitrobenzene to 2,2 -dichloroazobenzene and y -dinitrobenzene to 3,3 -diamiQoazobenzene. 

The NAD- and NADP-dependent dehydrogenases catalyze at least six different types of reactions simple hydride transfer, deamination of an amino acid to form an a-keto acid, oxidation of /3-hydroxy acids followed by decarboxylation of the /3-keto acid intermediate, oxidation of aldehydes, reduction of isolated double bonds, and the oxidation of carbon-nitrogen bonds (as with dihydrofolate reductase). 

Platinum, especially platinum oxide, has been used by many investigators (5), Platinum oxide, when used with aldehydes is apt to be deactivated before reduction is completed. Deactivation is inhibited by small amounts of ferrous or stannous chlorides (59,82). This type of promoter can also sharply curtail hydrogenolysis if it is a troublesome reaction (Rylander and Starrick, 1966). Deactivated systems can often be regenerated by shaking the reaction mixture with air (2,8,21 J3,96). The usefulness of this regenerative technique transcends aldehyde reductions it frequently is worth resorting to. 

PROBLEMS Identify the starting ketone or aldehyde you would use to prepare each of the following alcohols through reduction reactions ... 

The aerobic reduction of aryl and alkyl carboxylates to the corresponding aldehydes. The reaction involves formation of an acyl-AMP intermediate by reaction of the carboxylic acid with ATP NADPH then reduces this to the aldehyde (Li and Rosazza 1998 He et al. 2004). The oxidoreductase from Nocardia sp. is able to accept a range of substituted benzoic acids, naphthoic acids, and a few heterocyclic carboxylic acids (Li and Rosazza 1997). 

Zr compounds are also useful as Lewis acids for oxidation and reduction reactions. Cp2ZrH2 or Cp2Zr(0 Pr)2 catalyze the Meerwein-Ponndorf-Verley-type reduction and Oppenauer-type oxidation simultaneously in the presence of an allylic alcohol and benzaldehyde (Scheme 40).170 Zr(C)1 Bu)4 in the presence of excess l-(4-dimethylaminophenyl) ethanol is also an effective catalyst for the Meerwein-Ponndorf-Verley-type reduction.1 1 Similarly, Zr(0R)4 catalyze Oppenauer-type oxidation from benzylic alcohols to aldehydes or ketones in the presence of hydroperoxide.172,173... 

A similar reducing system is created by combining dilithium catecholate and trichlorosilane at —78° in tetrahydrofuran. It is speculated that the relatively unstable pentacoordinate bis(l,2-benzenediolato)hydridosilicate (61) is formed in situ and that it is this species that can reduce aldehydes and ketones, but not esters, to alcohols when they are added to the reaction mixture at 0° (Eq. 168).93 In a like manner, the dilithium salt of 2,2/-dihydroxybiphenyl, which forms a pentacoordinate intermediate that is stable enough to react at room temperature, can also be used to promote the reduction reaction. The alkoxides of aliphatic diols... 

Aryl aldehydes, alkane reduction, 71-72 Aryldiazonium salts, reduction of, 104 Aryl halides and triflates, reduction reaction, 32 Aryl ketone, allylation,... 

Catalysts and Catalyst Concentration. The most active catalyst for benzaldehyde reduction appears to be rhodium [Rh6(C0)i6 precursor], but iron [as Fe3(C0)i2] and ruthenium [as Ru3(C0)12] were also examined. The results of these experiments are shown in Table 1. Consistent with earlier results (12), the rhodium catalyst is by far the most active of the metals investigated and the ruthenium catalyst has almost zero activity. The latter is consistent with the fact that ruthenium produces only aldehydes during hydroformylation. Note that a synergistic effect of mixed metals does not appear to be present in aldehyde reduction as contrasted with the noticeable effects observed for the water-gas shift reaction (WGSR) and related reactions (13). 

CHEC-II(1996) <1996CHEC-II(8)345> covered a range of reactions of substituents, including hydrolyses of esters to carboxylic acids and geminal dihalides to aldehydes, reduction of aldehydes and halogens directly attached to the ring, O-methylation with diazomethane, and reduction of nitroso compounds. A selection of reactions which have... 

Aldehydes and ketones are readily reduced back to primary and secondary alcohols, respectively. In the case of ketones, although the reduction is reversible, ketoreductase utilizes NADPH, the concentration of which is higher than NADP+, and this drives the reaction toward the secondary alcohol. A good example is warfarin as shown in Figure 5.3 (19). However, aldehydes are further oxidized to carboxylic acids and carboxylic acids are not reduced back to aldehydes thus eliminating the aldehyde. Reductive metabolism of esters and amides also does not generally occur. 

In almost the same manner, tandem hydroformylation/aldol condensation aldol condensation of ketoolefins, such as p,y-unsaturated ketones, gives a single cyclization product under acid catalysis. Similar to the stepwise reaction, the in situ generated aldehyde preferentially acts as the electrophilic carbonyl component, while the ketone acts as the nucleophilic enol to form the five-membered ring product. Subsequent dehydration and hydrogenation of the resulting enone readily occurs under the reductive reaction conditions used (Scheme 30) [84],... 

In a related study, the oxidation-reduction sequence was carried out in the presence of an olefin (Scheme 21). Two products were formed. The major product resulted from the net reduction of the carboxylic acid to an aldehyde. The minor product resulted from trapping of the radical anion intermediate generated from the reduction reaction by the olefin. It should be noted that, in the absence of a trapping group, the acid can be selectively reduced to the aldehyde without any over-reduction. Although not in the scope of this review, this is a very useful transformation in its own right [35]. At this time, the yields of the cyclized products from the cyclization reaction of the radical anion with the olefin remain low. 

These are reduction reactions. Notice that the aldehyde is reduced to a primary alcohol and the ketone is reduced to a secondary alcohol. 

Reduction reactions mediated by microorganisms may include the reduction of nitro bonds, sulfoxide reduction, and reductive dehalogenation. Reduction of the nitro group to amine involves the intermediate formation of nitrase and hydroxy amino groups. Selected reductive reactions may involve the saturation of double bonds, reduction of aldehydes to alcohols or ketones to secondary alcohols, or of certain metals. The main reductive processes in the subsurface environment have been discussed earlier in this chapter. 

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