Bischler – Napieralski Cyclization – DMAP as Catalyst

1. A solution of the carbamate (1) (69 mg, 0.23 mmol) and DMAP (85 mg, 0.69 mol), in anhydrous dichloromethane (6 mL) is stirred at 0-5°C.  A 1.10 mol/dm³ solution of triflic anhydride (1.05 mL, 1.16 mmol) in anhydrous dichloromethane is prepared and this triflic anhydride solution (1.05 mL, 1.16 mmol) is added to this reaction mixture over 15 min.
2. The reaction mixture is stirred for a further 16 h, allowing the flask contents to warm to room temperature over this time period.
3. Dichloromethane (10 mL) is added to the  reaction mixture and the mixture is successively washed with saturated sodium carbonate solution (1 x 5 mL), aqueous acetic acid (20% v/v) (1 x 5 mL) and saturated sodium carbonate solution (1 x 5 mL).  The organic phase is dried (sodium sulfate), filtered and concentrated under reduced pressure to give a light brown solid.  Recrystallization (twice from methanol) affords anhydrocorinone (40 mg) as fine white needles, m.p. 236 - 238°C.  The mother liquors were subject to preparative thin layer chromatography (silica, benzene:acetone, 8:2 elution) to produce additional anhydrocorinone (13 mg, 88% combined yield).