Synthesis of <Emphasis Type="Italic">N</Emphasis>-[3-alkoxy-4-(hydroxy-, alkoxy-, or acyloxy)-benzylidene- and -phenylmethyl]biphenyl-2-amines

Condensation of aldehydes of the vanillin series (vanillin, vanillal, and ethers and esters derived therefrom) with biphenyl-2-amine in anhydrous methanol gave the corresponding Schiff bases which were reduced with Na[BH(OAc)₃] in benzene under mild conditions to obtain N-[3-alkoxy-4-(hydroxy-, alkoxy-, or acyloxy)phenylmethyl]biphenyl-2-amines.     

<Emphasis Type="Italic">N</Emphasis>-[(<Emphasis Type="Italic">E</Emphasis>)-3-alkoxy-4-hydroxy(alkoxy,alkanoyloxy, aroyloxy)-benzylidene]-4-phenoxyanilines

Condensation of 4-phenoxyaniline with benzaldehydes of the vanillin series in methanol gave the corresponding Schiff bases, N-[(E)-3-alkoxy-4-hydroxy(alkoxy, alkanoyloxy, aroyloxy)benzylidene]-4-phenoxyanilines.     

Chemical release control: Sulfonate esters from perfume and herbicide alcohols and p-styrenesulfonyl chloride

p-Styrenesulfonate esters of primary and secondary perfume alcohols and phenols, including citronellol, 1-menthol, borneol, β-phenethyl alcohol, eugenol, p-anisyl alcohol, cinnamyl alcohol, and geraniol, and herbicide alcohols such as 2,4-dichloro- and 2,4,5-trichlorophenoxy-ethanols were synthesized using p-styrenesulfonyl chloride in the presence of bases such as pyridine, triethylamine, sodium hydrogen carbonate, and sodium hydride. The hydrolytic behavior of sulfonate ester monomers and their copolymers with N-vinyl-2-pyrrolidone to liberate perfume and herbicide alcohols was structure-dependent, thereby affording chemical release control.     

Synthesis of hydroxybenzaldehyde derivatives containing an isoxazole heteroring

5-Phenyl(p-tolyl)isoxazole-3-carboxylic acids were synthesized starting from 3-hydroxyiminomethyl-5-phenyl(p-tolyl)isoxazoles, and their reactions with p-hydroxybenzaldehyde, vanillin, isovanillin, o-vanillin, and ethyl vanillin gave the corresponding esters. The latter were brought into condensation with aromatic amines to obtain Schiff bases which were reduced to amines.     

Synthesis,characterization & in vitro antimicrobial‐antioxidant studies of novel N,1‐diphenyl‐4,5‐dihydro‐1H‐1,2,4‐triazol‐3‐amine derivatives

A new series of 1,2,4‐triazole was designed, synthesized, and characterized as remarkable antimicrobial and antioxidant agents. These heterocycles have been prepared from the cyclization reactions of Schiff bases 3 ( a‐k ) with phenylhydrazine by refluxing under the alkaline medium. The Schiff bases in turn were realized in good yields from the condensation reactions of N‐phenylurea with different aromatic aldehydes. The structures of the intermediates 3 ( a‐k ) and final heterocycles 4 ( a‐k ) have been fully characterized through their spectral parameters.     

Chemosensors based on <Emphasis Type="Italic">N</Emphasis><Superscript>2</Superscript>-(anthracen-9-ylmethyl)-naphthalene-2,3-diamine

Condensation of N ²-(anthracen-9-ylmethyl)naphthalene-2,3-diamine with aromatic and heterocyclic aldehydes gave a series of the corresponding Schiff bases and N-(anthracen-9-ylmethyl)-substituted naphtho-[2,3-d]imidazoles. Study on the luminescence spectra and complexing ability of the condensation products revealed their sensor properties toward some heavy metal cations.     

Catalytic and antimicrobial activities of new ruthenium(II) unsymmetrical Schiff base complexes

Hexa-coordinated ruthenium(II) complexes of the type [Ru(CO)(PPh₃)(Z)(L)] [Z = PPh₃, pyridine (py) or piperidine (pip); L = anion of the Schiff base] have been prepared by reacting [RuHCl(CO)(PPh₃)₂(Z)] with tridentate Schiff bases derived by condensing anthranilic acid with acetylacetone, salicylaldehyde, o-vanillin and o-hydroxyacetophenone. The complexes were characterised by analytical and spectral (i.r., electronic, ¹H- and ³¹P-n.m.r.) data, and were found to be effective catalysts for oxidising primary alcohols to aldehydes in the presence of N-methylmorpholine-N-oxide (NMO) as co-oxidant. The Schiff bases and their ruthenium(II) complexes show growth inhibitory activity against pathogenic fungi Aspergillus flavus, Fusarium oxysporium and Rhizoctonia solani.     

Synthesis of enamino ketones from <Emphasis Type="Italic">N</Emphasis>-(2-vinyloxyalkyl)-ethane-1,2-diamines

Condensation of N-(2-vinyloxyethyl)ethane-1,2-diamine with aromatic aldehydes gave mixtures of 2-aryl-1-(2-vinyloxyethyl)imidazolidines and N-arylmethylidene-N′-(2-vinyloxyethyl)ethane-1,2-diamines in an overall yield of 79–84%, while analogous condensation with cyclic and acyclic ketones resulted in the formation of only the corresponding Schiff bases (yield 53–83%).     

Nitrile elimination and hydrogen rearrangement upon electron impact in schiff base peptide esters

A series of Schiff base peptide esters were examined by gas chromatography mass spectrometry. Electron impact induced elimination of aryl nitriles (ArCN) from Schiff bases , where R, R′ …are amino acid sidechains formed from aromatic aldehydes and peptide esters was shown to be associated with formation of C-terminal peptide fragments. Schiff base derivatives prepared from benzaldehyde and α-deuterobenzaldehyde with several peptide esters indicated that aryl nitrile elimination was accompanied by H(D) transfer to the α-C of the N-terminal amino acid residue. Of the many Schiff base peptide esters of different aldehydes studied, HCN elimination of the type observed in some nonpeptide Schiff bases could only be found among N-methyl pyrrolemethylidene derivatives.     

N-substitution in the 2-amino- and 2,7-diaminophenoxazin-3-one ring system. Application to the preparation of actinomycin D analogs

A method is described for the direct N²-monoalkylation of the 2-aminophenoxazin-3-one system by treatment with dimethylsulfonium methylide in DMSO-THF, which acts as a base by abstracting a proton from the 2-amino function to form a stabilized anion, which is then alkylated by reaction with an alkyl halide. Selective N⁷-monoalkylation of the 2,7-diaminophenoxazin-3-one system can be accomplished by reaction with aromatic aldehydes in glacial acetic acid to give Schiff bases, which are then reduced with dimethylamine borane. These reactions have been applied to the preparation of N²-benzyl- and 7-benzylaminoactinomycin D.     

Synthesis and serotonin antagonist and antianexity activities of pyrrolidine derivatives from 4-hydrazinyl-1-p-substituted phenyl-2,5-dihydro-1H-pyrrole-3-carbonitriles

Abstract   N-(p-substituted phenyl)-4-cyanopyrrolidin-3-ones and their corresponding hydrazines were prepared and used as starting materials to synthesize heterocyclic candidates as serotonin antagonist and antianexity agents. Condensation of hydrazines with selected aromatic aldehydes afforded the corresponding Schiff bases. The hydrazines were treated with phenyl isothiocyanate to afford the corresponding thiosemicarbazides, which were cyclized with ethyl bromoacetate to N-phenylthiazolidinones. The hydrazine was reacted with 1,2,4,5-tetrachlorophthalic anhydride to give the tetrachloroimide derivative. It was reacted with benzoyl acetonitrile, 2-(bismethylsulfanyl-methylene)malononitrile, 2-ethoxymethylenemalononitrile, or 2-cyano-3-ethoxyacrylic acid ethyl ester to afford the corresponding pyrazoline derivatives. Schiff bases were obtained by simple condensation of the hydrazine with different carbonyl compounds. All the compounds were screened for their serotonin antagonistic and antianexity activities, and they showed high activities compared to buspirone and diazepam as controls. Graphical abstract        

α-Pinene-type chiral Schiff bases as tridentate ligands in asymmetric addition reactions

A group of tridentate Schiff bases derived from (+)-α-pinene were synthesized. The steric effects in the transition state, the importance of π-π stacking interactions as well as the electronic effects of aryl aldehydes according to Hammett constant values in the enantioselective addition of Et₂Zn to aldehydes with the use of Schiff bases as chiral ligands are described. Also, a variety of aldehydes were cyanated using a catalyst prepared in situ from titanium tetraisopropoxide and chiral Schiff bases. The influence of a conjugated double-bond in the cyanation substrates on enantioselectivity was observed. The chemical structures of the chiral Schiff base-titanium alkoxide complexes are discussed based on their ¹H and ¹³C NMR spectra. 3D models of the Zn₂-complex catalyst and Ti-complex catalyst containing α-pinane-type Schiff bases based on X-ray diffraction experiments are postulated. The models presented were consistent with the reported chirality of the addition product and observed ee.     

Synthesis and biological activity of new 1,3,4-thiadiazole derivatives

The aminothiadiazole (II) on treatment with aromatic aldehydes yielded Schiff bases, which cyclized to thiazolidinone derivatives by reaction with thioglycolic acid. Reaction of II with phenyl isocyanate and phenyl isothiocyanate afforded the carbamide and carbothiamide derivatives, respectively, which on reaction with malonic acid in acetyl chloride gave barbituric and thiobarbituric acid derivatives. However, reaction of carbon disulfide and methyl iodide with II gave dithiocarbamidate derivative which on treatment with ethylenediamine or o-phenylenediamine gave the condensed N-imidazolylthiadiazolylamine derivatives.     

Coordination compounds of hydrazine derivatives with transition metals,part XVIII. Cobalt(II) and cobalt(III) chelates with schiff bases derived from hydrazine-S-methyldithiocarboxylate and thiosemicarbazide

Summary The reactions of aldehydic and ketonic Schiff bases derived from hydrazine-S-methyl dithiocarboxylate and thiosemicar-bazide with cobalt(II) acetate were investigated. Octahedral tris ligand cobalt(III) chelates were formed with aldehydic Schiff bases whereas tetrahedral bis ligand cobalt (II) chelates were isolated with ketonic Schiff bases.N-isopropylidene hydrazine-S-methyldithiocarboxylate, however, gave both octahedral tris cobalt(III) and tetrahedral bis cobalt(II) chelates. These results are interpreted in terms of the steric requirements of the Schiff base used.     

Spectral,magnetic, biological,and thermal studies of metal(II) complexes of some unsymmetrical Schiff bases

New nickel(II) and copper(II) complexes with unsymmetrical Schiff bases derived from aromatic 2-hydroxy aldehydes were synthesized and characterized by elemental analyses, melting points, ¹H-NMR, magnetic susceptibility, thermogravimetric analysis, differential scanning calorimetry (DSC), infrared (IR), and electronic spectral measurements. Comparison of IR spectra of the Schiff bases and their metal complexes indicated that the Schiff bases are tetradentate, coordinated via the two azomethine nitrogens and the two phenolic oxygens. Magnetic moments and electronic spectral data confirm square-planar geometry for the complexes. Thermal studies reveal a general decomposition pattern, whereby the complexes decomposed partially in a single step due to loss of part of the organic moiety. A single endothermic profile, corresponding to melting point, was observed from the DSC of all complexes, except those whose ligand contained the nitro group, which decomposed exothermally without melting. The Schiff bases and their complexes were screened in vitro against 10 human pathogenic bacteria. The metal(II) complexes exhibited higher antibacterial activity than their corresponding Schiff bases.     

Synthesis of Schiff bases from 1-naphthylamine and vanillin, vanillal, and their O-acyl derivatives

Previously unknown Schiff bases were synthesized by the condensation of 1-naphthylamine with vanillin, vanillal, and their O-acyl derivatives in ethanol.     

Diastereoselective addition of hypophosphorous acid to N‐(R)‐α‐methylbenzyl‐substituted schiff bases

The addition of hypophosphorous acid to an azomethine bond of N‐(R)‐α‐methylbenzyl Schiff bases of a variety of aldehydes led to the formation of N‐(R)‐α‐methylbenzylamino‐(S)‐methanephosphonous acids in 100% diastereoselectivity. This fact allows us to suggest the probable mechanism of the Strecker‐like reaction between hypophosphorous acid, an aldehyde, and (R)‐α‐methylbenzylamine. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:35–37, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20406     

Synthesis of (<Emphasis Type="Italic">E</Emphasis>)-<Emphasis Type="Italic">N</Emphasis>-(3-alkoxy-4-acyloxyphenylmethylene)-<Emphasis Type="Italic">N</Emphasis>-(<Emphasis Type="Italic">e</Emphasis>-cyclohexyl)amines

Previously unknown E isomers of azomethines (Schiff bases) were synthesized from vanillal and vanillin esters by their reaction with cyclohexylamine.     

Systematic studies on mechanochemical synthesis: Schiff bases from solid aromatic primary amines and aldehydes

A versatile and robust mechanochemical route to Aldehyde–Schiff base conversions has been established for a broad range of aldehydes via a simple cogrinding in mortar with a pestle under a solvent‐free, as well as solvent‐assisted, environment. The extent of amines reactivity under these conditions has also been explored, along with an examination of the possible connection between reactivity and electronic substituent effects. Results obtained demonstrated that the solvent‐free mechanochemical conversion of p‐toluidine and aromatic aldehydes to the corresponding Schiff bases proceeded more smoothly than the corresponding synthesis with 4‐aminobenzonitrile. The present approach not only provides good to excellent yields but also eliminates the disadvantages of the traditional synthesis of Schiff bases, such as the use of hazardous solvents, more or less demand of expensive catalysts, and looking for optimization on reaction conditions.     

Preparative synthesis of 4-hydroxy(alkyloyloxy, aryloyloxy)-3-methoxy(ethoxy)phenylmethylene(4-carboxyphenyl)amines

By reactions of vanillin, vanillal, and their esters with 4-aminobenzoic acid in methanol formerly unknown E-isomers of azomethines (Schiff’s bases) were prepared.