Thionyl Chloride → 3,4-Dihydropyrazino[1,2-a]benzimidazol-1(2H)-one

Participants

Reaction Conditions

Reaction Steps

A 100-mL single-neck round-bottomed flask equipped with a magnetic stirrer and reflux condenser was purged with nitrogen and charged with 152a (1.41 g, 6.84 mmol) and DMF (10 mL), and the reaction mixture was cooled to 0° C. A solution of thionyl chloride (896 mg, 7.53 mmol) in DMF (5 mL) was added dropwise. The reaction was heated at 150° C. for 2 h. After this time, the solvent was removed under reduced pressure. The resulting residue was partitioned between water (20 mL) and methylene chloride (20 mL). The layers were separated, and the aqueous phase was extracted with methylene chloride (2×20 mL). The organic extracts were combined, dried over sodium sulfate, filtered and concentrated under reduced pressure. The resulting residue was purified by flash chromatography to afford a 52% yield (672 mg) of 152b as a brown solid: mp>250° C.; 1H NMR (500 MHz, DMSO-d6) d 8.53 (s, 1H), 7.76 (d, 1H, J=9.0 Hz), 7.66 (d, 1H, J=9.0 Hz), 7.40 (t, 1H, J=9.0 Hz), 7.31 (t, 1H, J=9.0 Hz), 4.41 (t, 2H, J=6.0 Hz), 3.71 (m, 2H); MS (APCI+) m/z 188.4 (M+H).

Provenance & Evidence