H. A. H. El-Sherief

Utility and Synthetic Uses of Mannich Reaction: An Efficient Route for Synthesis of Thiadiazino‐[1,3,5][3,2‐a]benzimidazoles

Abstract The utilities of the Mannich reaction in synthetic organic chemistry are reviewed. The behaviors of Mannich reactions on several bifunctional heterocyclic compounds have been reported. A new class of heterocyclic compounds, thiadiazino[1,3,5][3,2‐a]benzimidazoles 12a–g, were obtained by reaction of 2‐mercaptobenzimidazole with primary aliphatic amines in a one‐step synthesis. An attempt to apply this reaction using primary aromatic amines lead to the formation of the well‐known Mannich bases 11a–g rather than the N‐substituted thiadiazines 13.

Studies on the Synthesis and Cyclization Reactions of2-(5-Amino-3-arylpyrazol-1-yl)-3-methylquinoxalines

A series of2-(5-amino-3-arylpyrazol-1-yl)-3-methylquinoxalines (2a–d)has been synthesized by the condensation of2-hydrazino-3-methylquinoxaline (1) with substitutedbenzoylacetonitriles and converted into the corresponding3,4-diaryl-1-(3-methylquinoxalin-2-yl)-4,8-dihydro-1H -pyrazolo[3,4-e ][1,4]thiazepin-7(6H )-ones(7a–d) and2-(3-aryl-4,5,6,7-tetrahydro-5-alkyl/aryl-1H -pyrazolo[3,4-d ]pyrimidin-1-yl)-3-methylquinoxalines(8a–e).

A Convenient One-Pot Synthesis of Pyrazolo[3,4-d]pyrimidines and s-Triazolo[3,4-b][1,3,5]thiadiazines

Abstract The reaction of 5-amino-3-aryl-1-phenylpyrazoles (1a-d) with formaldehyde and secondary amines in boiling ethanol gave the corresponding 4-alkylaminomethyl derivatives (2a-f) and bis-(4-pyrazolyl)methane (4a,b) as byproduct. Such reaction with primary aliphatic and aro matic amines at room temperature afforded 1,3,5-trisubstituted (5a-h) and 1,3.5,7-tetrasubstituted tetrahydropyrazolo[3,4-d]pyrimidines (8a-k) respectively in good yield. Similarily, the Mannich reaction of 5-mercapto-3-phenyl-1,2,4-triazole (9) with secondary amines, in boiling ethanol, and primary aromatic amines, at room temperature, gave 2 -substituted aminomethyl derivatives (10a-c) and (14a-g) respectively,while with primary aliphatic amines, p-toluidine and p-anisidine,at room temperature,and with other primary aromatic amines, in boiling ethanol, afforded the cyclized products 12,4-triazolo[3,4-b]thiadiazines (13a-e); (15f,g) and (15a-e), respectively.

An efficient and rapid intramolecular cyclization of a quadruple Mannich reaction for one-pot synthesis of pentaazaphenalenes and their antimicrobial activities

A simple, rapid and one-pot quadruple Mannich reaction has been developed for the synthesis of 2,5,7,9,11-pentaazaphenalenes via a three-component reaction of 6-amino-2-thioxo-2,3-dihydropyrimidin-4(1H)-one, formaldehyde and primary amines in ethanol at room temperature. The reaction products were obtained in very good to excellent yields using a simple work-up procedure. The regioselectivity of the reaction was studied using the electronic energy calculations which indicated that the corresponding products 2,5,7,9,11-pentaazaphenalenes are more favorable than the other isomeric products 3,5,8,10,11-pentaazaanthracenes and 2,5,7,8,10-pentazaphenanthrenes. The reaction mechanism was investigated and the structures of all the new compounds were confirmed using spectra and elemental analysis. In addition, all the synthesized compounds were screened for antimicrobial activity and showed a significant activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans, Geotrichum candidum and Trichophyton rubrum.