Regioselective synthesis and DFT study of novel fused heterocyclic utilizing Thermal heating and Microwave Irradiation

Abstract

Regioselective facile synthesis of innovative heterocycles from the reaction of 2-cyano-N-cyclohexylacetamide (3) with N, N- dimethylformamide dimethylacetal (DMF-DMA) to afford (E)-2-cyano-N-cyclohexyl-3-(dimethylamino) acrylamide (4) under microwave irradiation. Enaminonitrile 4 reacts with hydrazine derivatives affords the corresponding pyrazole derivatives 5a-c, furthermore the behavior of enaminone 4 reacts with guanidine to give the corresponding 2,4 diaminopyrimidine derivative (7). Moreover (E)-2-cyano-N-cyclohexyl-3-(dimethylamino) acrylamide (4) reacts with amino pyrazoles 8a-f, 1,2,4-aminotriazole (11) and 2-aminobenzimidazole (13) to afford the corresponding pyrazolo[1,5-a]pyrimidine 9a-f, andtriazolo[4,3-a]pyrimidine 12, pyrimido[1,2-a]benzimdazole14; respectively. Density functional theory calculations at the B3LYP/6-31G (d) levels of theory have been carried out to investigate the equilibrium geometry of the novel fused pyrazoles 5a and 9a. Moreover, the total energy, the energy of the HOMO and LUMO and Mulliken atomic charges were considered. Additionally,the measurements of their interactions with hydrazine hydrate to form fused pyrazoles 5a and 9a have been calculated. Also, comprehensive theoretical and experimental structural studies of 7-amino-Ncyclohexyl-2-methyl-3-phenylpyrazole[1,5-a]pyrimidine-6-carboxamide (9a) have been carried out by elemental analysis, FTIR, 1H NMR and Mass. Optimized molecular structure and harmonic vibrational frequencies have been reconnoitered by DFT/B3LYP and HF methods combined with 6-31G(d) basis set.