1-Chloroethyl chloroformate → 1'-isopropyl-1'H-spiro[piperidine-4,5'-pyrano[3,2-c]pyrazol]-7'(6'H)-one

Participants

Reaction Steps

1-Benzyl-1′-isopropyl-1′H-spiro[piperidine-4,5′-pyrano[3,2-c]pyrazol]-7′(6′H)-one (81 mg, 0.22 mmol) was dissolved in 10 mL 1,2-dichloroethane. Added 1-chloroethyl chloroformate (60 mL, 0.54 mmol) was added and the mixture was stirred 1 h at reflux then cooled to room temperature. The volatiles were removed under reduced pressure and the residue taken up in 10 mL methanol and heated at reflux for 1 h. The mixture was cooled to ambient temperature and the volatiles were removed under reduced pressure. The residue was taken up in 50 mL saturated aqueous sodium bicarbonate and extracted 2×30 mL ethyl acetate. The combined organic extracts were dried over sodium sulfate, filtered and concentrated to yield 46 mg (86%) of 1′-isopropyl-1′H-spiro[piperidine-4,5′-pyrano[3,2-c]pyrazol]-7′(6′H)-one as a white solid. 1H NMR (400 MHz, CD3OD) δ ppm 7.20 (s, 1H), 5.13 (spt, 1H), 2.93 (m, 2H), 2.80 (dt, J=12.8, 4.0 Hz, 2H), 2.64 (s, 2H), 2.02 (m, 2H), 1.63 (m, 2H), 1.40 (m, 6H); m/z (M+1)=250.2

Provenance & Evidence