Ethyl chloroformate → 5-Carboethoxy-3-(2,5-dimethylpyrrolyl)-1-methylpyrazole

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Reaction Steps

A solution of 3-(2,5-dimethylpyrrolyl)-1-methyl-pyrazole (5.0 g, 28.6 mmol) in dry tetrahydrofuran (250 mL) was cooled to -78° C. Then, n-butyllithium (19.5 mL, 1.6M, 31.2 mmol) was added dropwise over 15 min followed by stirring for 2 h at -78° to -60° C. Ethyl chloroformate (3.58 mL, 37.5 mmol) was added and the solution was warmed to room temperature and stirred 1 h. The solvent was removed at reduced pressure and the residue was partitioned between ether and water. Phases were separated and the organic layer was washed with brine, filtered through a cone of sodium sulfate, and concentrated to leave an oil. This residue was chromatographed on Silica Woelm®TSC (600 g, 15% ether-hexane) to give after an 850 mL forerun, 0.18 of an impurity in 500 mL and 4.69 g of oil in 700 mL. The oil was kugelrohr distilled, 100° to 110° C., (0.15 mm) to give 4.24 g, 60% of 5-carboethoxy-3-(2,5-dimethylpyrrolyl)-1-methylpyrazole as a clear oil; IR (neat) 1728, 1546, 1494, 1273, 1252 cm-1.

Provenance & Evidence