H-Y zeolite in toluene 8 h; Heating;

1: pyridine / 2 h / Ambient temperature 2: sodium carbonate / benzene / 5 h / Heating 3: 83 percent / 3,5-bis(ethoxycarbonyl)-2,6-dimethyl-1,4-dihydropyridine, silica gel / benzene / 0.5 h / Heating View Scheme