Azomethines ketimines

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). 

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). 

Additives may exert not only a physical but also a chemical influence on the coupling suspension long-chain aliphatic or cycloaliphatic amines RNH2, which react partially with the pigment molecules, will enhace the effect of other additives. The carbonyl function of the acetyl group is converted to a ketimine (azomethine) or, in the presence of the enol form, it reacts to form an alkylammonium enolate [5],... 

The azomethine-azomethine isomerization of 14 to 15 proceeds essentially intramolccular-ly (> 98 %), as shown by the reaction of ketimine 14h in a solution of triethylamine/methanol-r/4 (1 1), which gives 15h in 93% yield with less than 2% incorporation of deuterium in the product.14 The intermediate 2-azaallyl anion 12 apparently exists as a contact ion pair. 

Orlov et al. [112] concluded that the protonation took place on the azomethine group nitrogen atom on the basis of IR spectral data. In concentrated sulfuric acid, the formation of the only acidolysis product, 1,3-diarylpropan-l,2-one 107, was observed (Scheme 1.29). Orlov et al. [112] assumed that first protonation took place on the ketimine nitrogen atom (intermediate 106), but in strong acidic media the aziridine nitrogen atom is protonated as well, making the system unstable and promoting additional transformations. 

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). 

Johnston and coworkers reported a base-free aryl amination method based on radical additions to azomethines through nonconventional addition pathways (equation 6)42,43. By this route, the aryl radical adds to nitrogen, rather than to the carbon of the ketimines. For example, the ketimine prepared from o-bromophenethylamine and acetophenone was subjected to tributylstannane and the radical initiator AIBN to give the corresponding indoline in 87% yield. The only side product observed was the directly reduced compound. The fact that only the intramolecular radical addition can afford the high yield limited its application in synthesis of other arylamines. 

Zur Herstellung primarer Amine I eignen sich besonders Nickel- und Kobalt-Katalysa-toren, da an ihnen offensichtlich das primare Imin 11 (Ketimin)3 3 sehr viel schneller hydriert wird als das sekundare Imin III (Azomethin) bzw. Halbaminal IV, die sich in Folge-reaktionen bilden konnen4 ... 

The group of Gong and coworkers explored a biomimetic 1,3-dipolar cycloaddition between a-ketoester 79 and benzylamine derivatives 80 with electron-deficient olefins 81a,b to devise a straightforward route to proline derivatives 82 in high yields and enantioselectivities [49]. The proposed biomimetic three-component 1,3-dipolar cycloaddition proceeds as illustrated in Scheme 2.22a. The azomethine ylide B is formed, via a transamination from ketimine ester A, which is in turn prepared from a-ketoesters 79 and benzyl-amine derivatives 80 then, the 1,3-dipolar cycloaddition with electron-poor olefins 81a takes place. For this purpose, the bisphosphoric acid 83 was found to be the catalyst of choice to promote such transformation (Scheme 2.22b). Replacing dimethyl maleate (previously used as deficient olefins) by methyleneindolinones, the same approach could be extended to spirooxindoles synthesis in high yields and... 

In addition to the above equihbrium considerations, kinetic studies also have been used to elucidate the relative reactivities of imines. The effect of electron withdrawal and donation on the reactivity of the azomethine linkage has been found by investigating the rates of hydrolysis of several meta- and ara-substituted diphenyl ketimines. A plot of the logarithms of the rate constants of hydrolysis versus Hanunett sigma constants gives a p value of 2-00 . The positive p value indicates that the reactivity of the azomethine linkage is increased by electron-withdrawing substituents while substituents capable of electron donation decrease its reactivity. 

Several factors other than conjugation and inductive effects have been found to affect the reactivity of the azomethine linkage. Ortho and para hydroxy-substituted diaryl ketimines are unusually stable to-... 

Diaryl ketimines are more stable than alkyl aryl ketimines which in turn are more stable than the purely aliphatic ketimines since conjugation increases the thermodynamic stability of the azomethine linkage Benzophenone imine (3), with a melting point of 48°c is quite stable . Although the monoimine of j>-benzoquinone is very unstable, the diimine (4) is sufficiently stable to be studied spectroscopically . V... 

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