Potassium Fluoride → HCID 86679982, compound

Participants

Reaction Conditions

Reaction Steps

To a solution of 5-chloro-1-methyl-4-nitro-1H-pyrazole from Example 1 (355 mg, 2.2 mmol) and potassium fluoride (511 mg, 8.8 mmol) in dry DMSO (20 mL) was added (R)-tert-butyl 3-methylpiperazine-1-carboxylate (1.15 eq, 2.53 mmol) and the mixture was heated in the microwave at 100° C. for 10 hr. The mixture was partitioned between water (40 mL) and EtOAc (100 mL), the organic layer passed through a phase separation cartridge and concentrated under reduced pressure. Purification via silica gel column chromatography (0-100% EtOAc/isohexane) gave (S)-tert-butyl 3-methyl-4-(1-methyl-4-nitro-1H-pyrazol-5-yl)piperazine-1-carboxylate as an orange gum (627 mg). To a solution of this gum (212 mg, 0.65 mmol) in DCM (9 mL) was added trifluoroacetic acid (3 mL) and the mixture stirred at room temperature for 4 hr. The mixture was concentrated under reduced pressure and the residue was partitioned between water (20 mL) and DCM (30 mL). The organic layer was passed through a phase separation cartridge and concentrated under reduced pressure to give (S)-2-methyl-1-(1-methyl-4-nitro-1H-pyrazol-5-yl)piperazine as a yellow gum (120 mg). To a solution of this gum (119 mg, 0.53 mmol) and acetic acid (0.12 mL, 2.12 mmol) in MeOH (10 mL) was added aqueous formaldehyde (37 wt % in water, 0.17 mL, 2.12 mmol) and the mixture stirred at room temperature for 1 hr. Sodium cyanoborohydride (83 mg, 1.33 mmol) was then added and the mixture stirred at room temperature for 70 hr. The mixture was concentrated under reduced pressure and the residue was partitioned between water (20 mL) and DCM (30 mL). The organic layer was passed through a phase separation cartridge and concentrated under reduced pressure to give (S)-2,4-dimethyl-1-(1-methyl-4-nitro-1H-pyrazol-5-yl)piperazine as a yellow gum (109 mg). To a solution of this gum (108 mg, 0.45 mmol) and ammonium formate (209 mg, 3.6 mmol) in MeOH (10 mL) under nitrogen was added 10% palladium on carbon (48 mg, 0.45 mmol). The mixture was heated at 70° C. for 4 hr before being cooled, filtered and concentrated under reduced pressure. The residue was partitioned between water (20 mL) and DCM (50 mL) and the organic layer was separated, passed through a phase separation cartridge and concentrated under reduced pressure to give (S)-5-(2,4-dimethylpiperazin-1-yl)-1-methyl-1H-pyrazol-4-amine as a brown gum (94 mg, 62% over four steps). 1H NMR (400 MHz, CDCl3) δ 7.07 (s, 1H), 3.66 (s, 3H), 3.51-3.41 (m, 1H), 3.36 (td, J=5.7, 2.6 Hz, 1H), 2.94-2.84 (m, 3H), 2.36 (s, 3H), 2.28 (td, J=5.6, 3.0 Hz, 1H), 1.92 (dd, J=11.2, 9.8 Hz, 1H), 0.86 (d, J=6.3 Hz, 3H). Exchangeable NH2 not observed.

Provenance & Evidence