1-Chloro-N,N,2-trimethylprop-1-en-1-amine (89 μl, 0.63 mmol, 1.05 eq) was added dropwise to 4-methoxybenzoic acid (97 mg, 0.63 mmol, 1 eq) in DCM (1.5 ml) at ambient temperature. After stirring at ambient temperature for 1.5 h, a solution of tert-butyl 5-amino-3-[2-(3,5-dimethoxyphenyl)ethyl]pyrazole-1-carboxylate (199 mg, 0.57 mmol, 0.9 eq) and pyridine (142 μL, 1.74 mmol, 2.75 eq) in DCM (2 ml) was added to the reaction mixture and stirring was continued at ambient temperature for a further 3 h. A solution of TFA (386 μL, 5.2 mmol, 8.25 eq) in DCM (3.5 ml) was then added and stirring was continued at ambient temperature for 18 h. The reaction mixture was concentrated and the crude product was purified by reverse-phase prep. HPLC (basic) using a 33-53% gradient of acetonitrile in water containing 1% ammonium hydroxide solution. The clean fractions were taken and evaporated to afford the title compound as a colourless foamy solid (113 mg, 52% yield).
