Abstract
Various 5-arylidene derivatives were prepared via a Knoevenagel condensation-type reaction of aromatic/heteroaromatic aldehydes with rhodanine or thiazolidine-2,4-dione (TZD) catalyzed by EDA/AcOH under microwave heating. This convenient methodology is broad in scope (49 different products were obtained), delivers excellent yields (up to 99%), and requires low catalyst loading (10 mol %). This new approach was successfully applied to the synthesis of eight novel imidazo[1,2-a]pyridine-thiazolidinone hybrids in good to excellent yields (66-99%). A spectroscopic study of compounds 3n and 4n was carried out using torsion angle analysis and (13)C NMR chemical shift calculations to evaluate the absence of expected signals in the NMR spectra of these compounds. Their photophysical properties were also assessed, confirming a preference for a fluorescence mechanism via an ICT (intramolecular charge transfer) process.