m-Chloroperbenzoic acid → 5-(4,8-Dioxabicyclo[5.1.0]octan-5-yl)-1-methyl-4-nitro-pyrazole

Participants

Reaction Conditions

Reaction Steps

5-(1-Allyloxypent-4-enyl)-1-methyl-4-nitro-pyrazole (7.08 g, 28.2 mmol) was dissolved in DCM (910 mL) and the mixture degassed for 30 min before Grubbs 2nd generation catalyst (1.19 g, 1.41 mmol) was added. The reaction mixture was heated at 40° C. for 18 hr and concentrated under reduced pressure. Purification via silica gel column chromatography (0-10% EtOAc/isohexane) followed by reverse-phase preparative HPLC gave a mixture of isomers of 1-methyl-4-nitro-5-(tetrahydrooxepin-2-yl)pyrazole (66/34) as a clear oil (2.3 g). To a solution of this oil (2.3 g, 10.31 mmol) in DCM (50 mL) was added m-CPBA (70-75%, 3.56 g, 14.40 mmol) and the reaction mixture was stirred at room temperature for 4 hr. The reaction mixture was diluted with DCM (50 mL) and the organic layer was washed with saturated aqueous NaHCO3 (2×50 mL), water (50 mL) and brine (50 mL), dried over MgSO4, and concentrated under reduced pressure. Purification via silica gel column chromatography (0-30% EtOAc/isohexane) gave 5-(4,8-dioxabicyclo[5.1.0]octan-5-yl)-1-methyl-4-nitro-pyrazole as a colourless solid (1.0 g, 14% over two steps). 1H NMR (400 MHz, CDCl3) δ 8.02 (s, 1H), 5.51-5.44 (m, 1H), 4.02 (s, 3H), 3.93 (dt, J=12.7, 3.4 Hz, 1H), 3.62-3.53 (m, 1H), 3.35-3.27 (m, 2H), 2.58-2.51 (m, 1H), 2.41-2.25 (m, 3H).

Provenance & Evidence