Amines, reductive regeneration

Amines are regenerated from the protecting derivatives trichloro-t-butylcarbamates by treatment with sodium 2-thienyl teUurolate." The reagent is generated in a catalytic cycle by reduction of the corresponding diteUuride with sodium borohydride. 

Among the preparative routes to the octalin mixtures, the acid-catalyzed dehydration of 2-decalol3 and the metal-amine reduction of naphthalene4 appear most satisfactory. Apart from the purification method described in this preparation, pure A9,10-octalin has also been obtained by reaction of the octalin mixture with nitrosyl chloride. After separation of the adducts by fractional crystallization, the pure A9,10-octalin has been regenerated from its nitrosyl chloride adduct.3,5... 

Fig. (13). Photochemical reduction of carbon dioxide into formic acid using tricyclic tertiary amine as a sacrificial donor (a) Plant photosynthesis (b) amine radical cation formed from tricyclic amine (c) regeneration of amine by hydrogenation using Pd catalyst. Reproduced with permission from Ref. [58, 59]. 2011 McMillan Publishers Ltd.

Formed phenoxyls ArO are irreversibly consumed in coupling and ROO scavenging [251], The aminic antidegradant starts to be consumed according to processes reported in Sect. 3.1 only after the disappearance of all of the phenolic AO. QI are the principal products of transformation of PD (Sect. 3.1.1.3). A reductive regeneration of PD from QI proceeds in mixtures of PD and phenols on account of the oxidation of the phenol [3], This reactivity explains very effective cooperation between lid and 6-hydroxy-DHQ 16 (R = OH). QI 53 (R1,R2 = phenyl) arising from lid was reduced and the derivative of DHQ was oxidized into 105 [252],... 

The PBI complex with Pd(0) obtained by fixation of PdCl2 and subsequent reduction of Pd(2 + ) to Pd(0) by methanolic NaOH in a H2 medium is effective at amine reduction. One important advantage of the PBI-Pd(O) catalyst is its ability to be fully regenerated by washing the reduced substrate from the polymer with methanol. 

Scheme 16.7 Synthesis of aminoglycoside derivative 22 using azides as proteaing groups for amines. First, the amino groups of 18 were converted into azides by diazo transfer.After chemical remodeling of the aminoglycoside (one amino group was replaced by a hydroxy group), the amines were regenerated by Staudinger reduction ...

SchifT s bases A -Arylimides, Ar-N = CR2, prepared by reaction of aromatic amines with aliphatic or aromatic aldehydes and ketones. They are crystalline, weakly basic compounds which give hydrochlorides in non-aqueous solvents. With dilute aqueous acids the parent amine and carbonyl compounds are regenerated. Reduction with sodium and alcohol gives... 

The formation of an enamine from an a,a-disubstituted cyclopentanone and its reaction with methyl acrylate was used in a synthesis of clovene (JOS). In a synthetic route to aspidospermine, a cyclic enamine reacted with methyl acrylate to form an imonium salt, which regenerated a new cyclic enamine and allowed a subsequent internal enamine acylation reaction (309,310). The required cyclic enamine could not be obtained in this instance by base isomerization of the allylic amine precursor, but was obtained by mercuric acetate oxidation of its reduction product. Condensation of a dihydronaphthalene carboxylic ester with an enamine has also been reported (311). 

The palladium(O) complex undergoes first an oxydative addition of the aryl halide. Then a substitution reaction of the halide anion by the amine occurs at the metal. The resulting amino-complex would lose the imine with simultaneous formation of an hydropalladium. A reductive elimination from this 18-electrons complex would give the aromatic hydrocarbon and regenerate at the same time the initial catalyst. 

The mechanism involves a Pd(0) monocoordinate complex as the active species that undergoes oxidative addition to the aryl halide [141]. Thereafter, coordination of the amine to the palladium centre and deprotonation by the external base results in halide abstraction. After reductive elimination, the coupling product is obtained and the catalytic active species regenerated (Scheme 6.45). 

Cyclic chain termination by antioxidants. Oxidation of some substances, such as alcohols or aliphatic amines, gives rise to peroxyl radicals of multiple (oxidative and reductive) activity (see Chapters 7 and 9). In the systems containing such substances, antioxidants are regenerated in the reactions of chain termination. In other words, chain termination occurs as a catalytic cyclic process. The number of chain termination events depends on the proportion between the rates of inhibitor consumption and regeneration reactions. Multiple chain termination may take place, for instance, in polymers. Inhibitors of multiple chain termination are aromatic amines, nitroxyl radicals, and variable-valence metal compounds. 

In the presence of dissolved dioxygen, the hydroxyalkyl radicals are converted into the hydroxyperoxyl radicals very rapidly therefore, only hydroperoxyl and hydroxyalkylperoxyl radicals participate in the reduction of the aminyl radicals. The higher the temperature, the more effective the decomposition of the hydroxyperoxyl radicals and the higher the proportion of the H02 radicals participating in the regeneration of the amine. 

In other studies, imine reduction by [Ir(cod)(PPh3)2]BF4 in THF has been shown to be first order in each of the catalyst, the H2, and the substrate. Initial formation of [IrH2(imine)2(PPh3)2]+ was proposed to lead to amine and [Ir(im-ine)2(PPh3)2], Oxidative addition regenerates the Ir(III) species [34]. 

The Pd-catalyzed amination of / -rm-butylphenyl bromide with pyrrole in the presence of Pd(OAc)2, dppf and one equivalent of NaOr-Bu led to the Af-arylation product 88. A simplified version of the mechanism commences with the oxidative addition of p-te/t-butylphenyl bromide to Pd(0), giving rise to the palladium complex 89. Ligand exchange with pyrrole followed by deprotonation by the base (NaOr-Bu) results in amido complex 90. Reductive elimination of 90 then gives the amination product 88 with concomitant regeneration of Pd(0) catalyst. If the amine had a (3-hydride in amido complex 90, a (3-hydride elimination would be a competing pathway, although reductive elimination is faster than P-hydride elimination in most cases. 

The catalytic Pd complex and the aryl bromide together suggest the first step is oxidative addition of Pd(0) to the C5-Br bond. (The reduction of Pd(II) to Pd(0) can occur by coordination to the amine, p-hydride elimination to give a Pd(II)-H complex and an iminium ion, and deprotonation of Pd(IE)-H to give Pd(0).) The C10-C11 k bond can then insert into the C5-Pd bond to give the C5-C10 bond. P-Hydride elimination then gives the Cl 1-C12 n bond and a Pd(II)-H, which is deprotonated by the base to regenerate Pd(0). The overall reaction is a Heck reaction. 

D. Mandler and 1. Willner, Photosensitized NAD(P)H regeneration systems application in the reduction of butan-2-one, pyruvic, and acetoacetic acids and in the reductive amination of pyruvic and oxoglutaric acids to amino acids,... 

From a simplified scheme of reduction of the amide function it can be seen that the first stage is formation of an intermediate with oxygen and nitrogen atoms linked to an sp carbon. Such compounds tend to regenerate the original sp system by elimination of ammonia or an amine. Thus an aldehyde is formed and may be isolated, or reduced to an alcohol. Alternatively the product is an amine resulting from direct hydrogenolysis of the sp intermediate. 

In contrast, amino acid dehydrogenases comprise a well-known class of enzymes with industrial apphcations. An illustrative example is the Evonik (formerly Degussa) process for the synthesis of (S)-tert-leucine by reductive amination of trimethyl pyruvic acid (Scheme 6.12) [27]. The NADH cofactor is regenerated by coupling the reductive amination with FDH-catalyzed reduction of formate, which is added as the ammonium salt. 

An elegant four-enzyme cascade process was described by Nakajima et al. [28] for the deracemization of an a-amino acid (Scheme 6.13). It involved amine oxidase-catalyzed, (i )-selective oxidation of the amino acid to afford the ammonium salt of the a-keto acid and the unreacted (S)-enantiomer of the substrate. The keto acid then undergoes reductive amination, catalyzed by leucine dehydrogenase, to afford the (S)-amino acid. NADH cofactor regeneration is achieved with formate/FDH. The overall process affords the (S)-enantiomer in 95% yield and 99% e.e. from racemic starting material, formate and molecular oxygen, and the help of three enzymes in concert. A fourth enzyme, catalase, is added to decompose the hydrogen peroxide formed in the first step which otherwise would have a detrimental effect on the enzymes. 

Kinetics and mechanisms of oxidation of amines by Ru porphyrin complexes (particularly TMP species) have been reviewed [42]. rranx-Ru(0)2(TMP)/02/ CgHg/50°C/24h oxidised primary and secondary amines in the oxidation of ben-zylamine frani-Ru(NHj)jCHjPh)2(TMP) was isolated and characterised crystallo-graphically. A mechanism involving a two-electron oxidation of benzylamine to A-benzylideneamine by tra i-Ru(0)2(TMP) was proposed with concomitant reduction of the latter to Ru (0)(TMP). This disproportionates to tranx-Ru "(0)2(TMP) and Ru"(TMP) the latter regenerates Ru" (0)(TMP) with O, while the second two-electron oxidation of the imine to the aldehyde is effected by tranx-Ru(0)2(TMP) [597], (Table 5.1) [598]. 

However, since that time it has been recognised that the list of potentially carcinogenic amines is much longer and that these amines could actually be regenerated by metabolic (or chemical) reductive cleavage of those dyes that are made using these particular amines as their diazo components. (Figure 2.9 for Cl Acid Red 21.)... 

Bommarius, A. S., Drauz, K., Hummel, W., Kula, M.-R. and Wandrey, C. Some New Developments in Reductive Amination with Cofactor Regeneration. Biocatalysis 1994, 10, 37 7. 

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