p-Toluenesulfonic acid → 1-(3-(4-Chlorophenyl)-1,4,6,7-tetrahydro-5H-pyrazolo[4,3-c]pyridin-5-yl)ethan-1-one

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To a stirred solution of 50 g (0.35 mol) of N-acetyl-4-piperidone and 31 g (0.35 mol) of morpholine in benzene (350 mL) was added a catalytic amount (˜0.25 g) of p-toluenesulfonic acid. The mixture was heated to reflux for 10 h with a Dean-Stark trap. The solvent was removed under reduced pressure to give a brown oil. The crude product was diluted with CH2Cl2 (175 mL) and 50.0 mL (0.35 mol) of Et3N was added. The mixture was cooled to 0° C. and a solution of 45.0 mL (0.35 mol) of 4-chlorobenzoyl chloride in CH2Cl2 (50 mL) was added slowly by dropping funnel over 1 h. The mixture was allowed to warm to room temperature and stirred overnight. The reaction was then diluted with 1 N HCl (150 mL) and stirred vigorously for 3 h. The aqueous layer was extracted with CH2Cl2 (3×250 mL) and the combined extracts were dried over Na2SO4 and the solvent was removed under reduced pressure. The crude oil was diluted with EtOH (350 mL) and cooled to 0° C. To this stirred solution was slowly added 33.0 mL (1.06 mol) of hydrazine and the mixture was allowed to warm to room temperature and stir overnight during which time a white precipitate formed. The volume of the reaction was reduced to ˜150 mL and EtOAc (750 mL) was added to the mixture. The suspension was stirred vigorously for 2 h and was filtered then washed with EtOAc (2×200 mL) and dried under vacuum to afford 41.4 g (42% over 3 steps) of a pale yellow solid. TLC (silica, 5% MeOH/CH2Cl2): Rf=0.3. MS (electrospray), m/z calculated for C14H14ClN3O [M+H]+ 276.08, observed 276.0. 1H NMR (400 MHz, CDCl3, a mixture of amide rotamers): 7.65 (d, J=8.4 Hz, 2H), 7.64 (d, J=9.3 Hz, 2H), 7.58 (d, J=10.5 Hz, 2H), 7.55 (d, J=8.5 Hz, 2H), 4.94 (s, 2H), 4.78 (s, 2H), 4.08 (t, J=5.9 Hz, 2H), 3.90 (t, J=5.8 Hz, 2H), 3.02 (t, J=5.8 Hz, 2H), 2.96 (t, J=5.9 Hz, 2H), 2.36 (s, 3H), 2.31 (s, 3H).

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