Ahmed E. M. Mekky

The reaction of ethyl benzoylacetate with malononitrile: a novel synthesis of some pyridazine, pyridazino[2,3-a]quinazoline and pyrrole derivatives

Abstract Ethyl benzoylacetate undergoes Claisen condensation reaction with malononitrile to afford 2-cyano-5-phenyl-3,5-dioxopentanonitrile which could be cyclized into 2-aminopyran and coupled with diazonium salts to afford azo derivatives. These azo derivatives and those of ethyl benzoylacetate could be cyclized into 4-oxo-, 6-oxo- and 6-iminopyridazines and pyridazino[2,3- a ]quinazolines, respectively. The 6-iminopyridazines could be transformed into the 6-oxopyridazines. The imino- and oxopyridazines could be transformed into pyrrole derivatives.

Further studies on the reaction of ethyl benzoylacetate with malononitrile: synthesis of some novel pyridine and pyridazine derivatives

Abstract 2-Cyano-5-phenyl-3,5-dioxopentanonitrile undergoes alcoholysis followed by Knoevenagel condensation to afford ethyl 4,4-dicyano-3-phenyl-3-butenoate, a thermo dynamically controlled product, which undergoes cyclization in acid medium to afford 2,6-dihydroxy-4-phenylnicotinonitrile. Some azo derivatives of nicotinonitriles and of 2-aminopyran are described. 5-Arylazo-2-aminopyrans are transformed by acid treatment into pyridazine derivatives, whereas without the arylazo substituent pyridines are obtained.

3,4-Dimethyl-2,5-functionalized thieno[2,3-b]thiophenes: versatile precursors for novel bis-thiazoles

Synthesis of novel bis(thiazoles) 19–22, 24, 25, 30 and 31 is reported. Thus, reaction of the bis(α-bromoketones) 14 and 15 with the corresponding thioamide derivatives 16–18 in refluxing EtOH in the presence of triethylamine afforded 19–22 in good yields. On the other hand, the novel bis(thiazoles) 24 and 25 can be synthesized by the reaction of 14 and 15 with the corresponding p-chlorobenzaldehyde thiosemicarbazones 23 in refluxing EtOH. The novel isomeric bis(thiazoles) 30 and 31 can also be synthesized by a reaction of the corresponding bis(benzaldehyde thiosemicarbazones) 27 and 28 with p-chlorophenacyl bromide 29. Compounds 27 and 28 were obtained by condensation of the corresponding bis(aldehydes) 12 and 13 with thiosemicarbazide 26. GRAPHICAL ABSTRACT

Acidity constant and solvatochromic behavior of some pyrazolo[1,5-a]pyrimidin-2-amine derivatives.

The UV-visible electronic spectra of some azo compounds of pyrazolo[1,5-a]pyrimidin-2-amine have been studied. The solvatochromic behavior of these compounds was investigated by studying their spectra in pure organic solvents of different polarities such as cyclohexane carbon tetrachloride, chloroform, ethanol and DMF. These exhibits a red shift in its λmax with increase relative permittivity of medium changing from cyclohexane→carbon tetrachloride→chloroform→ethanol→DMF. The acid dissociation constants of these compounds were determined in aqueous-organic solvent mixtures such as acetone, methanol, ethanol and DMF. The ionization constants of the dyes in question depend largely on both the proportion and the nature of the organic solvent basicity contribute the major effects on the ionization process. In general, pKa values in all compounds decrease with increase relative permittivity of the medium. The acidity of studied azo compounds increases in the following order: p-NO2

Bis-(cyanoacetamide)alkanes in heterocyclic synthesis: synthesis of bis-heteryl(carboxymido)alkanes and bis-(heteryl)alkanes of thiophene, pyrrole, thiazole and pyrimidinone series

Bis-N-substituted cyanoacetamides 3a and b reacted with active methylene-containing compounds 2a–c and elemental sulfur to give bis-thiophene 4a and b and bis-pyrrole 6a and b derivatives. Compounds 4a and b reacted with ethyl cyanoacetate 2a to afford bis-thienopyrimidine derivatives 5a and b; on the other hand, 6a and b reacted with cyanothioacetamide 2c to give the corresponding bis-thioxopyrrolopyrimidine derivatives 7a and b. Compounds 7a and b reacted with methyl iodide to give the corresponding bis-2-S-methylpyrrolopyrimidine derivatives 8a and b, which could be, in turn, cyclized into the bis-pyrazolopyrrolopyrimidine derivatives 9a and b by refluxing with hydrazine hydrate. On the other hand, 7a and b reacted with ethyl chloroacetate to yield the corresponding bis-thienopyrrolopyrimidine derivatives 10a and b. Finally, compounds 3a and b reacted with phenylisothiocyanate and elemental sulfur to give the corresponding bis-2-thioxoaminothizole derivatives 11a and b.

Nano-optical Biosensors for Assessment of Food Contaminants

In the last decades, the optical biosensors have great attention, especially, when the biosensor is inserted into a good host such as tetraethoxyorthosilicate (TEOS) polymer and molecular imprinted polymer with no interference. This method gives a transparent nano-optical biosensor with new optical properties to increase the impact of the proposed analytical method which has wide linear range and very low detection limit. In this chapter, the transparent nano-optical sensor is inserted into TEOS polymer and imprinted template in molecular imprinted nanopolymer for the determination of different food contaminants such as different bacteria (Salmonella, Staphylococcus aureus and Campylobacter), Aflatoxin produced by different Aspergillus flavus and Aspergillus parasiticus species of fungi and E. coli bacteria. The nano-optical biosensors were used for the determination of food contaminants in different food samples with a high-performance analytical method.

Synthesis, reactions and DFT calculations of novel bis(chalcones) linked to a thienothiophene core through an oxyphenyl bridge

A synthesis of novel isomeric bis(chalcones) based-thienothiophene and study of their synthetic utilities as building blocks for novel bis(dihydroisoxazoles), bis(dihydropyrazoles) and bis(dihydropyrimidines) each linked to a thienothiophene core through an oxyphenyl bridge is reported. Density functional theory (DFT) calculations at the B3LYP/6-31G level of theory have been carried out to investigate the equilibrium geometry of the novel isomeric chalcones 7 and 10. Moreover, total energy, energy of the HOMO and LUMO and Mullikan atomic charges were calculated. In addition, the dipole moment and orientation of the two π-isoelectronic chalcones 7 and 10 have been measured and their interactions with hydrazine hydrate to form dihydropyrazoles have been studied.

Efficient, microwave-mediated synthesis of benzothiazole- and benzimidazole-based heterocycles

Abstract1-(Benzothiazol-2-yl)-3-(N,N-dimethylamino)-2-(phenylsulfonyl)prop-2-en-1-one (3) and 1-(1-methylbenzimidazol-2-yl)-3-(N,N-dimethylamino)-2-(phenylsulfonyl)prop-2-en-1-one (4) were obtained from the reaction of 1-(benzothiazothiazol-2-yl)-2-phenylsulfonyl-1-ethanone (1) and 1-(1-methyl-1H-benzimidazol-2-yl)-2-(phenylsulfonyl)-1-ethanone (2) with N,N-dimethylformamide dimethyl acetal, respectively. The enaminosulfones 3 and 4 were used as versatile building blocks for the synthesis of novel pyrazolo[1,5-a]pyrimidine and [1,2,4]-triazolo[1,5-a]pyramidine derivatives via their reactions with the appropriate aminopyrazoles and aminotriazole under both microwave and thermal reaction conditions. They have been also utilized as reactive synthons for the construction of novel pyrimido[1,2-a]benzimidazole, pyrido[1,2-a]benzimidazole, pyrimidine, isoxazole and pyrazole heterocycles pendent to benzothiazole and benzimidazole ring systems.