Functionalized reduced graphene oxide as a useful and efficient base catalyst for the preparation of 4H‐pyran and pyran‐like tacrine compounds and their antibacterial activity

An easy, effective and eco‐friendly one‐pot process for the preparation of 4H‐pyran compounds has been established by using a catalytic amount of reduced graphene oxide functionalized with diethylenetriamine (rGO‐DETA) in water under mild conditions. The functionalized catalyst was very effective for this one‐pot reaction and provided the desired products 1a–t with good to high yields (87%–97%) in short reaction times. Moreover, rGO‐DETA composite could be reused for four cycles without an obvious decrease in its performance. In the next step, two pyran derivatives 1f and 1h were used to synthesize the corresponding pyran‐like tacrine derivatives 3f and 3h via the reaction of cyclohexanone, aluminum trichloride in reflux of 1,2‐dichloroethane as solvent. Antibacterial activity of several of the prepared compounds was assessed against Gram‐positive and Gram‐negative bacteria by well and disk diffusion techniques. The 4H‐pyran 1g and 1s (2000 μg/ml) were effective against Micrococcus luteus as a Gram‐positive bacterium by recording a zone of inhibition of 15 and 16 mm, respectively. 4H‐pyran 1m showed moderate antibacterial behavior against both M. luteus and Serratia marcescens. Pyran‐like tacrine analog 3f (50 mg/ml) displayed antibacterial behavior towards Staphylococcus aureus as Gram‐positive and S. marcescens as Gram‐negative bacteria with zones of inhibition of 13 and 12 mm, respectively. 4H‐pyran 1j featured a minimum inhibitory concentration value of 39.06 μg/ml for M. luteus, which is the closest value to ampicillin.