Trifluoroacetic acid → 3-methyl-1-(tetrahydro-2H-pyran-2-yl)-1H-pyrazole

Participants

Reaction Conditions

Reaction Steps

A mixture of 3-methylpyrazole (3.0 g, 35.4 mmol), 3,4-dihydro-2H-pyrane (4.97 mL, 53.2 mmol) and TFA (0.02 mL, 0.260 mmol) was stirred at 85° C. for 6 h under an argon atmosphere. The RM was cooled to RT and NaH 60% in mineral oil (0.061 g, 1.524 mmol) was and the RM was stirred for 10 min. The RM was purified by bulb-to-bulb distillation to give 3-methyl-1-(tetrahydro-2H-pyran-2-yl)-1H-pyrazole (b.p. 150-170° C., 12 mbar). A solution of n-1.6 M BuLi in n-hexane (3.38 mL, 5.41 mmol) was added dropwise over 10 min to a solution of 3-methyl-1-(tetrahydro-2H-pyran-2-yl)-1H-pyrazole (1.0 g, 5.41 mmol) in THF (12 mL) at −70° C. under a nitrogen atmosphere and The RM was stirred for 10 min and then treated dropwise with 2-methoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (0.898 g, 5.69 mmol) and stirred at −70° C. for 1 h. The RM was allowed to warm to RT, treated with n-hexane and the product was filtered, dissolved in water (10 mL) and acidified to pH 6 with 10% aqueous citric acid. The water was evaporated off under reduced pressure and the aqueous residue extracted with EtOAc, dried over Na2SO4 and the solvent was evaporated off under reduced pressure to give the title product as a yellow resin. UPLC-MS (Condition 3) tR=0.56 min, m/z=211.2 [M+H]+.

Provenance & Evidence