Ketimines, Formation

Fernandez, E.J., Laguna, A., Lopez-de-Luzuriaga, J.M., Montiel, M Olmos, M.E. and Perez, J. (2006) Easy Ketimine Formation Assisted by Heteropolynudear Gold-ThaDium Complexes. Organometallics, 25(7), 1689—1695. 

Since ketimine formation is not possible in the reductive alkylation of secondary amines, this reaction must involve the hydrogenolysis of an alcoholamine. However, if either carbon a to the starting carbonyl has a hydrogen available, the enamine formation is possible. 

There is one example of an inorganic analogue of ketimine formation (equation 96). If requisite, primary amido complexes were available, this could be a useful synthetic method. 

Fig. 3.10. Aldimine and ketimine formation mechanism by the addition of an amino acid on the aldehyde or ketone function of a sugar...

Pong Bi Bi reaction mechanism. As they contain PLP, the mechanism is almost certainly similar to that known for the animal aminotransferases (Fig. 1). Details of this mechanism are discussed by Braunstein (1973) and by Metzler (1977). The apoenzyme moiety determines substrate specificity and confers high catalytic efficiency, as well as suppressing side reactions and eliminating the metal requirement characteristic of nonenzymatic transamination. Initially the amino acid binds to an anchoring site on the enzyme. Condensation then takes place between the amino acid and the enzyme pyridoxal-lysine imine to form an aldimine. Following further rearrangements, a ketimine is produced. Ketimine formation is then followed by a hydrolysis to... 

This reaction is however retarded by the presence of inert solvents due to dilution effects. The presence of ketones has also been shown to retard the reactions either due to pseudo-SchilTs-base or ketimine formation. 

Figure 4. Pyridoxal phosphate + amino acid as a Schiff base. (P) indicates a phosphate group. Bonds around the a-carbon can react as follows a, removal of to form semiquinoid intermediate which may then react in transamination (through ketimine formation), elimination, or racemization b, decarboxylation c, side chain cleavage.

The acid-catalyzed reaction of acetophenone with acyclic secondary amines results in the formation of the expected enamine and a rearrangement product. The latter product arises from the transfer of one of the amino N-alkyl groups to the cnamine s carbon to produce a ketimine (53a). 

Petrow described the formation of 3-iminoketones from 3-keto-aldehydes and aniline. Cyclization in the presence of aniline hydrochloride and ZnCh smoothly provides the desired quinoline 26. Bis-imine 24 is the proposed intermediate that undergoes cyclization. The aldimine is more reactive than the ketimine toward cyclization thus, cyclization on the aldimine occurs. When the bis-imine is not formed, partial aniline migration can occur which results in mixtures of cyclized products. 

We have previously discussed that keto-aldehydes react with anilines first at the aldehyde carbon to form the aldimine. Subsequent condensation with another aniline formed a bis-imine or enamino-imine. The aniline of the ketimine normally cyclizes on the aldimine (24 —> 26). Conversely, cyclization of the aldimine could be forced with minimal aniline migration to the ketimine using PPA (30 —> 31). The use of unsymmetrical ketones has not been thoroughly explored a few examples are cited below. One-pot enamine formation and cyclization occurred when aniline 48 was reacted with dione 49 in the presence of catalytic p-TsOH and heat. Imine formation occurred at the less-hindered ketone, and cyclization with attack on the reactive carbonyl was preferred. ... 

Optically pure a-amino acids can be converted to 1,2-diamines by a route that involves the preliminary formation of N-protected a-aminonitriles through the intermediate amides. The addition of organometallic reagents to these a-aminonitriles gives a-amino ketimines, which are then reduced in situ to 1,2-diamines. However, this route has been scarcely applied to acychc a-aminonitriles. As a matter of fact, the sequential addition of methylmag-... 

C. Reactions not involving P=0 or P=S Groups.—Enamine phosphine oxides (45) have been prepared by the addition of amines to 1-alkynyl-phosphine oxides, and the reactions of their anions with various electrophiles have been reported. - With ketones a Wittig-type reaction leads to the formation of a/3-unsaturated ketones, in 53—70% yield, while with epoxides cyclopropyl ketimines are formed. A Diels-Alder reaction of l-phenyl-A -phospholen-l-oxide (46) with 1,4-diacetoxybutadiene has been used in the preparation of l-phenyl-benzo[/>]phosphole (47), as... 

Aziridines have been synthesized, albeit in low yield, by copper-catalyzed decomposition of ethyl diazoacetate in the presence of an inline 260). It seems that such a carbenoid cyclopropanation reaction has not been realized with other diazo compounds. The recently described preparation of 1,2,3-trisubstituted aziridines by reaction of phenyldiazomethane with N-alkyl aldimines or ketimines in the presence of zinc iodide 261 > most certainly does not proceed through carbenoid intermediates rather, the metal salt serves to activate the imine to nucleophilic attack from the diazo carbon. Replacement of Znl2 by one of the traditional copper catalysts resulted in formation of imidazoline derivatives via an intermediate azomethine ylide261). 

Ketimines were successfully nitrosated by treatment with nitrosyl chloride in cold carbon tetrachloride resulting in the formation of N-nitrosoimines (Scheme 3.25) [201],... 

While this example of the Robinson annulation is clearly not enantioselec-tive, the same antibody converts the mero-ketone [120] into the Wieland-Miescher (WM) decalenedione product kcM = 0.086 min-1 and Km = 2.34 mM at 25°C, parameters that give an impressive ER of 3.6 x 106. Good evidence suggests that the mechanism of the reaction involves the formation of a ketimine with the e-amino group of a buried lysine residue in the antibody, as shown in Fig. 39. Most significantly, the reaction delivers the ( )-(+)-WM product in 96% ee (by polarimetry) and in 95% ee by nmr and hplc analysis for a 100 mg scale reaction. A recent report tells that this antibody is to be made commercially available at a cost of 100 for 10 mg. The realization of that objective would mark the start of a new era of application of abzymes to organic stereoselective synthesis. 

Formally related reactions are observed when anthracene [210] or arylole-fines [211-213] are reduced in the presence of carboxylic acid derivatives such as anhydrides, esters, amides, or nitriles. Under these conditions, mono- or diacylated compounds are obtained. It is interesting to note that the yield of acylated products largely depends on the counterion of the reduced hydrocarbon species. It is especially high when lithium is used, which is supposed to prevent hydrodimerization of the carboxylic acid by ion-pair formation. In contrast to alkylation, acylation is assumed to prefer an Sn2 mechanism. However, it is not clear if the radical anion or the dianion are the reactive species. The addition of nitriles is usually followed by hydrolysis of the resulting ketimines [211-213]. 

The electrolysis of asymmetric ketones 43 led to the formation of isomers and stereoisomers. Kinetic measurements for the formation of ketimine 43 in saturated ammoniacal methanol indicated that at least 12 h of the reaction time were required to reach the equilibrium in which approximately 40% of 42 was converted into the ketimine 43. However, the electrolysis was completed within 2.5 h and the products 44 were isolated in 50-76% yields. It seems that the sluggish equilibrium gives a significant concentration of ketimine 43 which is oxidized by the 1 generated at the anode, and the equilibrium is shifted towards formation of the product 44. 2,5-Dihydro-IH-imidazols of type 44, which were unsubstituted on nitrogen, are rare compounds. They can be hydrolyzed with hydrochloric acid to afford the corresponding a-amino ketones as versatile synthetic intermediates for a wide variety of heterocyclic compounds, that are otherwise difficult to prepare. 

Prior to imide formation, the imide-aryl ether ketimine copolymers were converted to the imide-aryl ether ketone analogue by hydrolysis of the ketimine moiety with para-toluene sulfonic acid hydrate (PTS) according to a literature procedure [51,52,57-59]. The copolymers were dissolved in NMP and heated to 50 °C and subjected to excess PTS for 8 h. The reaction mixtures were isolated in excess water and then rinsed with methanol and dried in a vacuum oven to afford the amic ester-aryl ether ether ketone copolymer, 2e (Scheme 8.)... 

Furthermore, the N-alkylation of 2-aminobenzyl alcohol 114 with ketones 115 in the presence of [IrCl(cod)]2 and KOH gave quinoline derivatives 116 (Equation 10.28) [52]. The reaction may be initiated by the formation of ketimine from 114 and 115, and the ketimine thus formed is oxidized by Ir catalyst and the 114 which serves as a hydrogen acceptor giving the corresponding aldehyde, which is eventually converted into quinoline 116 through intramolecular aldol-type condensation. 

Hydrolysis of the new imine then allows formation of a ketone as part of an a-keto acid, and an amine which is the previously mentioned pyridoxamine 5 -phosphate. Since this imine is the product from an amine and a ketone, it is termed a ketimine. These reactions are reversible in nature, allowing amino acids to be converted into keto acids, and keto acids to be converted into amino acids (see Section 15.6). 

PLP-dependent enzymes are inhibited by a great variety of enzyme-activated inhibitors that react by several distinctly different chemical mechanisms.11 Here are a few. The naturally occurring gabaculline mimics y-aminobutyrate (Gaba) and inhibits y-aminobutyrate aminotransferase as well as other PLP-dependent enzymes. The inhibitor follows the normal catalytic pathway as far as the ketimine. There, a proton is lost from the inhibitor permitting formation of a stable benzene ring and leaving the inhibitor stuck in the active site ... 

Group d). The fourth group of PLP-dependent reactions are thought to depend upon formation of the ketimine intermediate of Eq. 14-28. In this form the original a-hydrogen of the amino acid has been removed and the C = NH+ bond of the ketimine is polarized in a direction that favors electron withdrawal from the amino acid into the imine group. 

Deprotection of polystyrene-bound ketimines has been achieved by treatment with aqueous HC1 or TFA in THF [260,313], or by benzophenone oxime formation with hydroxylamine hydrochloride [314,315] (Figure 10.17). 

However, for aliphatic low-molecular-weight members of this class, oligomerization and/or polymerization, formation of gem-dithiols and enethiolization are often observed. The purification steps can be tedious and the obtention of pure products difficult. There is still a need for progress in this field. Although much less used, another general method whose scope appears important [127] involves the reaction of ketimine... 

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