Microwave-Assisted Synthesis of Bis(enaminoketones): Versatile Precursors for Novel Bis(pyrazoles)viaRegioselective 1,3-Dipolar Cycloaddition with Nitrileimines

Utility of 2-Chloro-N-arylacetamide and 1,1'-(Piperazine-1,4-diyl)bis(2-chloroethanone) as Versatile Precursors for Novel Mono- and Bis[thienopyridines]

A series of novel thieno[2,3-b]pyridines linked to N-aryl carboxamides or (carbonylphenoxy)-N-(aryl)acetamides, as well as bis(thieno[2,3-b]pyridines) linked to piperazine core via methanone or carbonylphenoxyethanone units, were synthesized by treating the appropriate chloroacetyl- or bis-bromoacetyl derivatives with 2-mercaptonicotinonitrile derivatives in ethanolic sodium ethoxide at reflux. The spectral data were used to determine the compositions of novel compounds.

[3 + n] Cycloaddition Reactions: A Milestone Approach for Elaborating Pyridazine of Potential Interest in Medicinal Chemistry and Optoelectronics

During the last few decades, pyridazine derivatives have emerged as privileged structures in heterocyclic chemistry, both because of their excellent chemistry and because of their potential applications in medicinal chemistry and optoelectronics. This review is focused on the recent advances in [3 + n] cycloaddition reactions in the pyridazine series as well as their medicinal chemistry and optoelectronic applications over the last ten years. The stereochemistry and regiochemistry of the cycloaddition reactions are discussed. Applications in optoelectronics (in particular, as fluorescent materials and sensors) and medicinal chemistry (in particular, antimicrobials and anticancer) are also reviewed.

Microwave assisted synthesis of bis and tris(ω-bromoacetophenones): versatile precursors for novel bis(imidazo[1,2-a]pyridines), bis(imidazo[1,2-a]pyrimidines) and their tris-analogs

Background

α-Bromination of the side chain of aromatic ketones using NBS in the presence of p-toluenesulfonic acid (p-TsOH) in acetonitrile is very common. However, regioselective bromination of bis and tris(ω-bromoacetophenones) with NBS in the presence of p-TsOH in acetonitrile under microwave irradiation is quite novel. The bis- and tris(ω-bromoacetophenones) are used in synthesis of bis and tris(heterocycles). bis(heterocycles) have received a great deal of attention, because many biologically active natural and synthetic products have molecular symmetry. The use of the pressurized microwave irradiation is very advantageous to many syntheses and provide a large rate enhancement.

Results

Bis and tris(ω-bromoacetophenones) were obtained as single monobrominated derivatives in a shorter time than the conventional conditions. The results clearly demonstrate the better reactivity and selectivity of NBS/p-TsOH/CH₃CN as a brominating mixture under microwave conditions. The reaction of bis and tris(ω-bromoacetophenone) with 2-aminopyridine and 2-aminopyrimidine proceeded smoothly in a mixture of anhydrous ethanol and DMF under reflux or using 300 W/105°C/ 20 min microwave irradiation conditions to afford the corresponding bis(imidazo[1,2-a]pyridine), bis(imidazo[1,2-a]pyrimidine) and tris(imidazo[1,2-a]pyridine) derivatives in moderate to excellent yields. The carbonyl analogue of the targeted bis(imidazopyridines) could be synthesized by the reaction of N,N-dimethyl-N'-(pyridin-2-yl)formimidamide with bis(ω-bromoacetophenone) in refluxing ethanol. The structures of the newly synthesized compounds were confirmed by their spectral data as well as their elemental analyses.

Conclusion

In conclusion, selective α-bromination of bis- and tris(acetophenones) has been accomplished efficiently utilizing NBS/p-TsOH/CH₃CN under microwave irradiation. In addition, a facile synthesis of novel series of bis- and tris(imidazopyridine) and bis(imidazopyrimidine) derivatives.