Azomethine derivatives

Aldimines, Ketimines, and Related Compounds as Dipolarophiles Reactions of aldimines with nitrile oxides proceed readily to give 1,2,4-oxadiazolines independently of the nature of substituents both in dipole and dipolarophile molecules. 1,2,4-Oxadiazolines were prepared by the regiospe-cihc 1,3-dipolar cycloaddition of nitrile oxides with fluoro-substituted aldimines (295). Phosphorylnitrile oxides gave with azomethines, PhCH NR, phosphory-lated 1,2,4-oxadiazolines 129 (296). Expected 1,2,4-oxadiazolines were also obtained from azomethines, derived from 4-formylcoumarine (179) and 1,3-diphenylpyrazole-4-carbaldehyde (297). 

The chromium complexes of some azomethine derivatives are used as solvent dyes. Cl Solvent Yellow 32 (6.231) is an example, obtained by condensing one mole of salicyl-aldehyde with the appropriate amine, followed by treatment with one equivalent of chromium. 

Depending on the substitution pattern, either azomethine derivatives (X1 = O or N-, X3 = N-) or methine derivatives (X1 = X3 = C must be defined. 

The alkylation of caclohexanone has been studied as a model reaction in detail. Generally, enamino compounds (126) are allowed to react with alkyl halides or a, 3-unsaturated carbonyl compounds. The enamine (126a) is prepared directly from the ketone and a chiral secondary amine (route A). A metalloenamine (126b) can be synthesized from chiral azomethine, derived from the model ketone and a primary chiral amine (route B). The primary amine used for the formation of (126b) must possess an oxygen function. This oxygen function plays a key role in the coordination of the lithium ion in the complex (126b). 

Epoxidation also proceeds (Eq. 141) under mild conditions and with high stereoselectivity (95 5 erythro threo) despite the deactivating effect of the fluorine atom [361]. At a higher oxidation level, the Lausanne group described chemistry of a metallated azomethine derived from a,/Lunsaturated-a-fluoroaldehydes [362]. Highly flexible chemistry allowed alkylation at nitrogen, or at the (fluori-nated) -position, or at the -position (Fig. 8). 

Azomethine derived ferroelectric liquid crystals As DOBAMBC, many ferroelectric LC s were prepared utilizing amyl alcohol as the chiral source. The reason for the small spontaneous polarization of DOBAMBC is the separation between the C=0 dipole moment and the chiral carbon. This effect can be explained by the intramolecular rotation or vibration of the carbonyl dipole moment relative to the chiral carbon, because they are not adjacent. There are some rules linking the molecular structure and the direction of the spontaneous polarization (minus or plus). In order to reduce the separation between the carbonyl dipole moment and the chiral carbon, ferroelectric LC s were synthesized utilizing a secondary alcohol as the chiral source. Ferroelectric LC s with large spontaneous polarizations have large dipole moments at the chiral centre. Ferroelectric LC s with halogen or nitrile units connected directly to the chiral carbon were synthesized from chiral lactic acids or amino acids. 

The success achieved with the Rh(II)-catalyzed transformations of -oximino diazo carbonyl compounds prompted our group to study some additional systems where the C-N 7i-bond was configurationally locked so that azomethine ylide formation would readily occur. Toward this end, we investigated the Rh(II)-catalyzed behavior of isoxazoline 186 in the presence of DMAD. This reaction afforded the azomethine-derived cycloadduct 187 as a 4 1 mixture of diastereomers in 65% yield. A similar transformation occurred using the a-diazoacetophenone derivative 188 which produced isoxazolo[3,2-a]isoquinoline 189 as a 2 1 mixture of diastereomers in 82% yield.84... 

The hydrolysis in acetone-water of the azomethine derivatives 184 to the corresponding amides has been investigated by Ugi et al., (1962). An SN1 mechanism, probably involving nitrilium chloride ion-pairs, has... 

Lithium enamides—lithium salts of azomethine derivatives... 

Similarly, the enamine salt 15 is obtained by lithiation of 14 (equation 5). In both cases the lower steric hindrance leads to higher stability of the enaminic system33 where the double bond is formed on the less substituted carbon. The Af-metalated enamines 11 and 15 are enolate analogs and their contribution to the respective tautomer mixture of the lithium salts of azomethine derivatives will be discussed below. Normant and coworkers34 also reported complete regioselectivity in alkylations of ketimines that are derived from methyl ketones. The base for this lithiation is an active dialkylamide—the product of reaction of metallic lithium with dialkylamine in benzene/HMPA. Under these conditions ( hyperbasic media ), the imine compound of methyl ketones 14 loses a proton from the methyl group and the lithium salt 15 reacts with various electrophiles or is oxidized with iodine to yield, after hydrolysis, 16 and 17, respectively (equation 5). 

Lithium enamides—lithium salts of azomethine derivatives Shimon Shatzmiller and Rami Lidor 1507... 

The electrochemical behavior of azomethine derivatives, e.g., oximes, of heteroaromatic carbonyl compounds is much like that of the corresponding benzene derivatives.91 Pyridine aldoximes271-274 and ketoximes275 are reduced in acid solution by a four-electron reaction to the amine. The reaction mechanism is probably, as in other oximes,01 a reduction of the protonated compound with cleavage of the N-0 bond, followed by saturation of the C=N double bond. The amine is often further reducible at a more negative potential (Section VI, E). 

An azomethine derivative is generally more easily reducible than the parent carbonyl compound and this can be exploited in cases where the equilibrium between the carbonyl compound and the azomethine derivative favors the former. By reduction at a potential at which the azomethine derivative, but not the carbonyl compound, is reduced, the azomethine is continuously removed from the equilibrium by reduction to amine as it is formed.91 This technique has been used for the preparation of 2-anilinomethylthiazole.276... 

Electrochemistry of azomethines derived from heterocycles 89MI13. 

EPR was stabilized by azomethine dyes [168] by rolling them at 160 °C for 5 h under pressure. Smith et al. [169] have found that these dyes function as quenchers of O2. The azomethine derivatives may be considered as a-substituted anilines... 

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