Azomethine bond

Electrophilic attack on the 5-position gives formation of an azomethinic bond and elimination of a molecule of water. 

Aryl-2-phenyl-4,5-dihydropyridazin-3(2//)-ones react either with phenylmagnesium bromide or with phenyllithium to give 6-aryl-2,6-diphenyl-l,4,5,6-tetrahydropyridazin-3(2//)-ones (135) (products of 1,2-addition to the azomethine bond), while 2-methyl-6-phenyl-4,5-dihydropyridazine-3(2//)-one reacts with two equivalents of phenylmagnesium bromide at the carbonyl and azomethine group to produce 2-methyl-3,3,6,6-tetraphenyl-hexahydropyridazine (136) (Scheme 53) (80JPR617). 

Synthesis of complex 1. The pentadentate salen catalyst 1 was synthesized as described (9). In short, the tosylated 2-[2-(2-methoxyethoxy)-ethoxy]-ethanol 2 (10) was reacted with 2,4-dihydroxybenzaldehyde 3 to yield 4-alkoxy salicylaldehyde 4 after chromatographic purification (eq. 1). Subsequent condensation of 4 with 1,3-diaminopropanol yielded water-soluble salen ligand 5 in sufficient purity and 89% yield (11). The formation of an azomethine bond is indicated by a shift of the NMR signal for the carbonyl carbon from 194.4 ppm in aldehyde 4 to 166.4 ppm for the imino carbon in 5. The pentadentate ligand 5 was then treated with copper(ll) acetate in methanol to obtain the dinuclear copper(ll) complex 1 as a green solid (eq. 2) (11). 

Simple 5-pyrimidineboronic acid is not trivial to make because the requisite lithiopyrimidine would add to the azomethine bond. The tendency towards these side reactions is less severe in case of 2,4-di-fert-butoxy-5-bromopyrimidine (20) and the halogen-metal exchange can be conducted at -75 °C [29], The nucleophilic attack towards the azomethine bond is retarded due to the steric hindrance. Therefore, the halogen-metal exchange of 2,4-di- -butoxy-5-bromopyrimidine (20) followed by quenching with n-butylborate, basic hydrolysis and... 

For the halogen-metal exchange reaction of bulkier halopyrimidines, steric hindrance retards the nucleophilic attack at the azomethine bond. As a consequence, halogen-metal exchange of 5-bromo-2,4-di-r-butoxypyrimidine (43) with n-BuLi could be carried out at -75 °C [20]. The resulting lithiated pyrimidine was then treated with n-butylborate followed by basic hydrolysis and acidification to provide 2,4-di-f-butoxy-5-pyrimidineboronic acid (44). 5-Bromopyrimidine 43 was prepared from 5-bromouracil in two steps consisting of a dehydroxy-halogenation with phosphorus oxychloride and an SnAt displacement with sodium r-butoxide. 

So, despite the presence of the blocking phenyl group at C-4 in the starting material, the initial addition of the amide ion preferentially takes place in the N-3-C-4 azomethine bond at C-4, i.e., formation of 81. 2-Flu-... 

It seems very likely that the initial addition of the alkyl amine takes place at the activated N-C(2) azomethine bond and that the reaction sequence occurs in a similar way to that described in Scheme IILl. When the reactions were carried out in boiling ethanol, besides the N -phenyl-N -alkyl exchange, deethoxycarbonylation occurs. Deethoxycarbonylation is the sole reaction that takes place on treatment of 3 with r-butylamine (82JOC498). 

C=N bonds in acylhydrazone groups, which are formed by the condensation of hydrazides with carbonyl groups, exhibit reversibility under mild conditions. Like polyimines, polymers with acylhydrazone functionalities exhibit dynamic aspects through the reversibihty of the azomethine bond. Skene and Lehn have reported the synthesis of polyacylhydrazones and their dynamic features (Scheme 8.3) [23]. High molecular weight polyacylhydrazone 13 was prepared by the condensation of the corresponding dihydrazide and dialdehyde in the presence of an acid catalyst. When 13 was treated with aryl dialdehyde 14 or aryl dihydrazide 15 in... 

When 5,6-dihydro-l,3-thiazines 24 are treated with sodium borohydride, the carbonyl group is reduced to the alcohol 142 and the azomethine bond remains intact (Equation 8) <2000GHE862>. This is in contrast to 477-1,3-thiazines where the azomethine bond does react <1964JHC300>. 

Sodium borohydride reduction of the azomethine bond has been noted for 3H-2-benzazepines (75JA4682,76HCA623) and for ll//-dibenz[6,e]azepines (65CCC445). 

Ir and nmr analysis of the condensation products of primary amines with aldehydes and ketones are in favor of the Schiff-base structure (46a). Nevertheless, these substances react with aryl azides in chloroform solution in the tautomeric enamine form (46b) yielding aminotriaiolines.206 225- 227 It proves that the dipolarophilic activity of an enamine olefin bond is much greater than that of an azomethine bond. 

Scheme 4.2) does not produce diazepine derivatives, but 2-(2-oxyphenyl)benzimi-dazole 6 was found to be the only product isolated. However, there are known data on the interaction between o-PDA and orr/zooxybenzalacetone 7 (the structure of which is similar to that of ortho-oxychalcone) resulting in the formation of benzodiazepine 8 [9]. The reaction involves an intramolecular cyclization in which the hydroxyl group and the azomethine bond participate ... 

Some papers are devoted to the modification of 2,3-dihydrodiazepines with respect to the C = N bond. The oxidation reaction involving the azomethine bond and leading to the formation of epoxide [107] was referred to earlier. The interaction of 2,2,4-trimethyl-2,3-dihydrobenzodiazepine 76 with 2-(oxyphenylimino)-1-phenylethanone 119 is described in [112] (Scheme 4.38). The reaction is carried out in benzene at room temperature and apart from the C = N bond involves the 4-methyl group (compound 120). 

Interesting results are obtained from the interaction of 2,3-dihydrodiazepines 104 with 2-diazo-l,3-diphenylpropane-l,3-dione 127. The reaction involves both the secondary amino group and the azomethine bond, thus leading to the formation of compounds 128 and 129 [115] (Scheme 4.41). 

According to x-ray diffraction data, the ligands contained in these complexes are coordinated only through tellurium atoms. One of the causes contributing to the decrease in dentacity of the discussed ligands is the formation of an intramolecular Te—N bond [912,913], which decreases the electron-donor activity of the N atom found in the azomethinic bond. 

Hollingsworth and Petrow, who assumed the trans-anil (134) structure for the condensation product of aniline and 2-hydroxy-methylenecyclohexanone, found that cyclization to 7,8,9,10-tetra-hydrophenanthridine could be achieved by heating with formic acid. Since this reagent reduces azomethine bonds, it was argued that favorable stereochemistry is achieved by reduction170 and, in fact, the secondary amine (135) can be isolated.171 However, later work has shown that the anil is, in fact, cis (136) and that cyclization to... 

Cyolane Azomethine bond - funqicide Picric acid Trinitrotoluene (TNT)... 

Due to the importance of azines and diazines in pharmaceutical industry and biorganic chemistry, the development of selective and efficient metallation protocols for substituted compounds has been the object of deep investigations.1 - The main difficulty in this context is that the 7r-deficient heteroaromatics undergo a facile nucleophilic addition to the azomethine bond with alkyllithiums.184-186 For this reason sterically hindered non-nucleophilic lithium amides (lithium diisopropylamide and lithium 2,2,6,6-tetramethylpiperidide)181 182 are usually employed in the selective deprotonation of heterocyclic compounds. In some cases the use of both unimetallic183 and... 

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