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A stirred solution of methyl 5-amino-2-furoate (1.4 g, 10 mmol) and 1-hexen-3-one (7 mL, 60 mmol) in benzene (50 mL) was heated to reflux for 2 h. The reaction mixture was concentrated under reduced pressure to afford a crude oil. Purification by flash column chromatography (silica, 2:1 hexanes/ethyl acetate) provided methyl 4-amino-5-butyryl-1-hydroxycyclohexa-2,4-diene-1-carboxylate (1.25 g): 1H NMR (300 MHz, CDCl3): δ 6.26–6.23 (m, 1H), 6.09–6.05 (m, 1H), 3.80 (s, 3H), 3.02–2.96 (m, 1H), 2.89–2.84 (m, 1H), 2.42–2.37 (m, 2H) 1.64–1.57 (m, 2H), 0.96–0.88 (m, 3H).

1. temperatureto reflux for 2 h
2. concentrationThe reaction mixture was concentrated under reduced pressure
3. customto afford a crude oil
4. customPurification by flash column chromatography (silica, 2:1 hexanes/ethyl acetate)