Oxalyl chloride → 1-(4-fluorophenyl)-7,8-dihydro-1H-benzo[f]indazol-5(6H)-one

Participants

Reaction Steps

A solution of 4-(1-(4-fluorophenyl)-1H-indazol-6-yl)butanoic acid (3, R1=4-Fluorophenyl) (13.86 g, 46.5 mmol) in DCM (225 mL) was treated with oxalyl dichloride (2M in DCM) (25.6 mL, 51.1 mmol). Two drops of DMF were added and the mixture was stirred for about 45 min at rt. A second portion of oxalyl dichloride (2M in DCM) (4.65 mL, 9.29 mmol) was added followed by 1 drop DMF. After about 15 min the solvent was removed under reduced pressure. The material was dissolved in DCM (225 mL) and the flask was fitted with a reflux condenser. Aluminum trichloride (8.2 g, 61.5 mmol) was added and the mixture was stirred for about 30 min. A second portion of aluminum trichloride (7.67 g, 57.5 mmol) was added to the mixture and stirring was continued for about 30 min. The reaction was quenched by slow addition of ice in small portions over about 30-45 min with vigorous stirring. After addition of about 50 g of ice, the biphasic mixture was transferred to a separatory funnel and the layers were separated. The aqueous layer was extracted with DCM (30 mL) and the combined organic solutions were washed with water (75 mL), 0.5 N aq. sodium hydroxide (100 mL) and brine (50 mL). The organic mixture was dried over MgSO4, filtered and concentrated under reduced pressure to a solid. The material was purified on silica gel (330 g) using a gradient of 0-15% EtOAc in DCM. Fractions containing >95% desired product were combined and concentrated under reduced pressure. Fractions containing desired product contaminated with the minor regioisomer [1-(4-fluorophenyl)-7,8-dihydro-1H-benzo[g]indazol-9(6H)-one] were combined and concentrated under reduced pressure separately. The residue was purified on silica gel (80 g) using a gradient of 0-10% EtOAc in DCM. Fractions containing >95% desired product were combined with those from the first column and concentrated under reduced pressure to yield 1-(4-fluorophenyl)-7,8-dihydro-1H-benzo[f]indazol-5(6H)-one (4, R1=4-Fluorophenyl) (8.73 g, 67%); LC/MS, method 3, Rt=2.43 min, MS m/z 281 (M+H)+. 1H NMR (400 MHz, DMSO) δ 8.52 (d, J=0.9 Hz, 1H), 8.49 (s, 1H), 7.86-7.78 (m, 2H), 7.69 (s, 1H), 7.51-7.41 (m, 2H), 3.12-3.09 (m, 2H), 2.70-2.63 (m, 2H), 2.11-2.02 (m, 2H). Note: 1H NMR shows ˜4% minor regioisomer.

Provenance & Evidence