Azomethines reactions

These compounds are soluble in ether, are comparatively stable, and exhibit many of the reactions of Grignard reagents but are more reactive. Because of their greater reactivity, organohthium compounds can often be used where Grignard reagents fail thus they add to the azomethine linkage in pyridines or... 

Azomethines add with great ease and stereospecificity to carbon-carbon double bonds affording pyrazolidines. They also add to carbon-carbon triple bonds with the formation of pyrazolines. Benzimidazolium iV-imines, e.g. (622), are a special case of azomethines. Its reaction with DMAD yields l-(2-methylaminophenyl)pyrazole (624), which is formed by cleavage of the initial adduct (623) (75JHC225). 

Burger s criss-cross cycloaddition reaction of hexafluoracetone-azine (76S349) is also a synthetic method of the [CNN + CC] class. In turn, the azomethines thus produced, (625) and (626) (79LA133), can react with alkenes and alkynes to yield azapentalene derivatives (627) and (628), or isomerize to A -pyrazolines (629) which subsequently lose HCF3 to afford pyrazoles (630 Scheme 56) (82MI40401). 

Aroylaziridines (32) and aromatic aldehydes react to give oxazolidines (33), the stereochemistry of which suggests reaction very largely through the trans-azomethine ylide, irrespective of the aziridine configuration (70JCS(C)2383). 

Diaziridine, 3-benzyl-1,3-dimethyl-inversion, 7, 7 Diaziridine, 1,2-dialkyl-reaction with iodides, 7, 217 thermal decomposition, 7, 217 Diaziridine, dibenzoyl-rearrangement, 7, 214 Diaziridine, 3,3-dimethyl-Raman spectra, 7, 202 Diaziridine, fluoro-synthesis, 7, 232 Diaziridines acylation, 7, 213 from azomethines, 7, 231 calculations, 7, 198 from chloramine, 7, 230 cycloaddition reactions, 7, 28 electron diffraction, 7, 19 199 c/s-fused NMR, 7, 201 hydrolysis, 7, 216 inversion stability, 7, 200... 

Aromatic nitro compounds are often strongly colored. They frequently produce characteristic, colored, quinoid derivatives on reaction with alkali or compounds with reactive methylene groups. Reduction to primary aryl amines followed by diazotization and coupling with phenols yields azo dyestuffs. Aryl amines can also react with aldehydes with formation of Schiff s bases to yield azomethines. 

Trifluoromethyl-substituted 1,3-dipoles of the allyl type. Trifluoromethyl-substituted azomethine imines ate readily available on reaction of hexafluo-... 

The azomethine imines exhibit the typical cycloaddition behavior expected of 1,3-dipolar species [fSJ] Numerous [3+2] cycloaddition reactions have been performed [201 204] Tetracyanoethylene adds to azomethine imines across the nitnle function instead of the C=C double bond This reaction is a rare example of this type of periselectivity [208] (equation 47)... 

Diethylamino-4-(4-methoxyphenyl)-isothiazole 5,5-dioxide 6 is (95T(51)2455) a highly reactive partner in 1,3-dipolar cycloadditions with several dipoles. Azomethine yhdes, such as oxazolones 7 and miinchnones 8, afforded with 6 bicychc pyrrolo[3,4-d]isothiazole 5,5-dioxides 9, 10, 11 in satisfactory yield. The regioselectivity of the reaction was excellent. The thermal behavior of these new bicychc systems was investigated. When heated at their melting point or shghtly above, triarylpyrroles 12, 13 were obtained through SOj and AtiV-diethylcyanamide ehmination. 

By further reaction of the selenazole-pyrazolones with p-nitro-sodialkylanilines a number of pyrazolone-azomethines (18) was pre-... 

For the reactions of other 1,3-dipoles, the catalyst-induced control of the enantio-selectivity is achieved by other principles. Both for the metal-catalyzed reactions of azomethine ylides, carbonyl ylides and nitrile oxides the catalyst is crucial for the in situ formation of the 1,3-dipole from a precursor. After formation the 1,3-di-pole is coordinated to the catalyst because of a favored chelation and/or stabiliza-... 

For azomethine ylides and carbonyl ylides, the diastereoselectivity is more complex as the presence of an additional chiral center in the product allows for the formation of four diastereomers. Since the few reactions that are described in this chapter of these dipoles give rise to only one diastereomer, this topic will not be mentioned further here [10]. 

Cobalt, Manganese, and Silver Catalysts for Reactions of Azomethine Ylides... 

The first report on metal-catalyzed asymmetric azomethine ylide cycloaddition reactions appeared some years before this topic was described for other 1,3-dipolar cycloaddition reactions [86]. However, since then the activity in this area has been very limited in spite of the fact that azomethine ylides are often stabilized by metal salts as shown in Scheme 6.40. 

Grigg et al. have found that chiral cobalt and manganese complexes are capable of inducing enantioselectivity in 1,3-dipolar cycloaddition reactions of azomethine... 

In a more recent publication the same group mentions that Ag(I) salts in combination with chiral phosphine ligands can catalyze the 1,3-dipolar cycloaddition involving the azomethine precursor 64b and methyl vinyl ketone (Scheme 6.43) [87]. The reaction, which presumably also required a stoichiometric amount of the catalyst, proceeds to give 65b in a good yield with 70% ee. 

Although the first metal-catalyzed asymmetric 1,3-dipolar cycloaddition reaction involved azomethine ylides, there has not been any significant activity in this area since then. The reactions that were described implied one of more equivalents of the chiral catalyst, and further development into a catalytic version has not been reported. 

When 2,2-dimethylpropanal is used to prepare the azomethine moiety, the corresponding azaallyl anion may be obtained when l,8-diazabicyclo[5.4.0]undec-7-ene/lithium bromide is used as base. The subsequent addition to various enones or methyl ( )-2-butenoate proceeds with anti selectivity, presumably via a chelated enolate. However, no reaction occurs when triethylamine is used as the base, whereas lithium diisopropylamide as the base leads to the formation of a cycloadduct, e.g., dimethyl 5-isopropyl-3-methyl-2,4-pyrrolidinedicarboxylate using methyl ( )-2-butenoate as the enone84 89,384. 

Huisgen et al. (1960, 1977 b) found that (i )-4-chlorobenzenediazocyanide reacts with 9-diazofluorene to give the azomethine imine 6.38 in 93 % yield (Scheme 6-28). Huisgen et al. interpret this reaction in terms of the electrophilicity of the diazocyanide at its a-nitrogen atom (not 0 ) and the nucleophilic character of 9-diazofluorene, as shown in the bipolar mesomeric structure 6.37. 

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