Microwave-Assisted Synthesis, DFT Calculations, and Crystal Structures of Three Series of Five-Membered Heterocyclic Monoimine Compounds

Three series of five-membered heterocyclic Schiff bases were synthesized by the condensation of 2-acetylpyrrole, 2-acetylthiophene, and 2-acetylfuran with substituted anilines under microwave irradiation. All compounds were fully characterized by 1H NMR and IR spectra and elemental analyses, and the structures of six compounds were determined by X-ray single crystal diffraction. The reactions of 2-acetylpyrrole and 2-acetylthiophene with anilines gave 1:1 condensation products, whereas the condensations with 2-acetylfuran involved 2 equiv of substituted anilines and were accompanied by transformation of the furan ring to pyrrole via Paal–Knorr reaction. A probable reaction mechanism was proposed.