Microwave-Assisted Oxidative Aromatization of Hantzsch 1,4-Dihydro­pyridines using Manganese Dioxide

4-Aryl- and 4-alkyl-1,4-dihydropyridines, prepared by microwave-assisted Hantzsch reaction, are readily and efficiently aromatized in only one minute using commercial manganese dioxide in the absence of an inorganic support at 100 °C under microwave irradiation. This rapid procedure is more efficient than microwave-assisted aromatization using Pd/C, iodine or o-iodoxybenzoic acid (IBX) and gives the dehydrogenated or 4-dealkylated product in 91-100% yield (13 examples).