Pyrazole → (2R,5R)-4-Benzyl-2-methyl-5-pyrazol-1-ylmethyl-piperazine-1-carboxylic acid tert-butyl ester

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Reaction Steps

A solution of methanesulfonic anhydride (0.65 g, 3.72 mmol) in DCM (5 mL) was added slowly to a solution of (2R,5R)-4-benzyl-5-hydroxymethyl-2-methyl-piperazine-1-carboxylic acid tert-butyl ester (1.08 g, 3.38 mmol) and triethylamine (1.42 mL, 1.02 g, 10.1 mmol) in DCM (10 mL) with stirring under nitrogen and external ice bath cooling. Stirring was continued at 0° C. for 2 h then pyrazole (0.3 g, 4.4 mmol) was added in one portion. Stirring at 20° C. was continued for 18 h, then mixture was partitioned between saturated aqueous NaHCO3 (40 mL) and DCM (3×20 mL). Combined organic extracts were dried (Na2SO4) and evaporated in vacuo to give an oil. Chromatography (SiO2; gradient elution with 0-40% Et2O in 40-60 petroleum ether) gave the title compound (0.811 g) as an oil. MS: [M+H]+=371.

Provenance & Evidence