Morpholine → 3-(4-Chloro-3-methyl-phenyl)-1,4,6,7-tetrahydro-pyrazolo[4,3-c]pyridine-5-carboxylic acid tert-butyl ester

Participants

Reaction Conditions

Reaction Steps

To a stirred solution of 55.8 g (0.28 mol) of 4-oxo-piperidine-1-carboxylic acid tert-butyl ester and 25.7 g (0.29 mol) of morpholine in benzene (125 mL) was added a catalytic amount (˜0.25 g) of p-toluenesulfonic acid. The mixture was heated to reflux for 10 h under a Dean-Stark trap. The solvent was removed under reduced pressure to give a brown oil. The crude product was diluted with CH2Cl2 (400 mL), and 46.83 mL (0.34 mol) of Et3N was added. The mixture was cooled to 0° C., and a solution of 4-chloro-3-methyl-benzoyl chloride (0.35 mol) in CH2Cl2 (200 mL) was added slowly by dropping funnel over 2 h. The reaction mixture was poured over water (400 mL) and the CH2Cl2 layer was separated, dried (Na2SO4), and concentrated. The resulting oil was taken up in EtOH (400 mL) and treated with 35 mL of hydrazine at 0° C. The reaction mixture was allowed to warm to room temperature and stirred for 17 h, during which time a white precipitate formed. The volume of the reaction mixture was reduced to ˜150 mL, and Et2O (750 mL) was added. The suspension was stirred vigorously for 2 h and was filtered then washed with Et2O (2×200 mL) and dried under vacuum to afford 50.74 g (52% over 3 steps) of 3-(4-chloro-3-methyl-phenyl)-1,4,6,7-tetrahydro-pyrazolo[4,3-c]pyridine-5-carboxylic acid tert-butyl ester as a pale orange solid. MS (electrospray): exact mass calculated for C18H22ClN3O2, 347.1; m/z found, 348.1 [M+H]+. 1H NMR (400 MHz, CDCl3): 7.26-7.43 (m, 4H), 4.65 (br s, 2H), 3.73 (br s, 2H), 2.77 (br s, 2H), 2.34 (s, 3H), 1.49 (s, 9H).

Provenance & Evidence