title: Regioselective synthesis and ab initio calculations of fused heterocycles thermally and under microwave irradiation.
abstract: Pyrazolo[1,5-a]pyrimidine, triazolo[1,5-a]pyrimidine, and pyrimido[1,2-a]benzimidazole, pyrido[1,2-a]benzimidazole ring systems incorporating phenylsulfonyl moiety were synthesized via the reaction of 3-(N,N-dimethylamino)-1-(thiophen-2-yl)-2-(phenylsulfonyl)prop-2-en-1-one derivatives with the appropriate aminoazoles as 1,3-binucleophiles and 1H-benzimidazol-2-ylacetonitrile using conventional methods as well as microwave irradiation. The regioselectivity of the cyclocondensation reactions was confirmed both experimentally by alternative synthesis of reaction products and theoretically using ab initio quantum chemical calculations namely the Density Functional Theory (DFT). The theoretical work was carried out using the Becke, three parameter, Lee-Yang-Parr hybrid functional (B3LYP) combined with the 6-311++G(d,p) basis set. It was found that the final cyclocondensation reaction product depends mainly on the initial addition to the activated double bond by the nitrogen atom of the 1,3-binucleophiles that has the higher electron density.
authors.affiliation: Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt.
authors.forename: Mostafa E
authors.initials: ME
authors.lastname: Salem
authors.affiliation: Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt; Institute of Physics, Rostock University, 18051 Rostock, Germany; Steinbeis GmbH & Co. KG für Technologietransfer, 70174 Stuttgart, Germany.
authors.forename: Ashour A
authors.initials: AA
authors.lastname: Ahmed
authors.affiliation: Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt; Department of Chemistry, Faculty of Applied Science, Umm Al-Qura University, Makkah Almukkarramah, Saudi Arabia.
authors.forename: Mohamed R
authors.initials: MR
authors.lastname: Shaaban
authors.affiliation: Department of Materials Science and Engineering (MSE), Cornell University, Ithaca, NY 14853, USA; Gas Processing Center, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar. Electronic address: mfshibl@qu.edu.qa.
authors.forename: Mohamed F
authors.initials: MF
authors.lastname: Shibl
authors.affiliation: Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt.
authors.forename: Ahmad M
authors.initials: AM
authors.lastname: Farag
mesh_terms: D001562:Benzimidazoles / Q000138:chemical synthesis* / Q000737:chemistry; D003500:Cyclization; D008872:Microwaves; D008958:Models, Molecular; D011743:Pyrimidines / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism; D013450:Sulfones / Q000138:chemical synthesis* / Q000737:chemistry; D013696:Temperature
chemical_list: D001562:Benzimidazoles; D011743:Pyrimidines; D013450:Sulfones
keywords: Alterative synthesis; Cyclocondensation; DFT calculations; Regioselectivity; Sulfones