General procedure for the synthesis of 6-(4-aminophenyl)-4,5-dihydro-5-methyl-3(2H)-pyridazinone from 4-(4-aminophenyl)-3-methyl-4-oxobutanoic acid hydrochloride: hydrazine hydrate (1.40 mL, 28.7 mmol) was added to an ethanolic solution of intermediate 3 (2.69 g, 11.04 mmol, dissolved in 70 mL of ethanol), the The reaction mixture was heated to reflux at 80 °C for 18 hours. After completion of the reaction, the mixture was concentrated in vacuum and the residue was ground with ethyl acetate to afford the target product Intermediate 7 in 1.46 g yield, 65%. The product was characterized by 1H NMR (300 MHz, CD3OD): δ [ppm] = 1.13 (d, 3H), 2.33 (d, 1H), 2.66 (dd, 1H), 3.28-3.40 (m, 1H), 6.68 (d, 2H), 7.56 (d, 2H). analysis by UPLC-MS (Method 3) showed a retention time R = 0.47 min and 100% purity. m/z (M + H)+ = 204 as measured by MS (ESIpos).
