Acetic Anhydride → 1-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)ethanone

Participants

Reaction Steps

To a stirred solution of 6,7-dimethoxy-1,2, 3,4-tetrahydroisoquinoline (3.00 g, 15.4 mmol, 1.00 equiv) in anhydrous pyridine (100 mL) under argon at room temperature was added acetic anhydride (14.5 mL, 154 mmol, 10.0 equiv) over 15 min. The resulting mixture was stirred at room temperature for 2 h, and then at reflux for 6 h. The volatiles were removed by rotary evaporation at 80° C. under high vacuum. The residue was flash chromatographed on silica gel (MeOH-CH2Cl2 8:92) to afford 3.21 g (89%) of viscous brown oil. The 1H NMR spectrum reflected the presence of two slowly interconverting conformers in a ratio of 1.2 :1 at room temperature. 1H NMR (300 MHz, CDCl3) for conformer 1: δ 2.18 (s, 3 H), 2.83 (t, J=5.9 Hz, 2 H), 3.67 (t, J=5.9 Hz, 2 H), 3.86 (s, 3 H), 3.87 (s, 3 H), 4.66 (s, 2 H), 6.63 (s, 1 H), 6.65(s, 1 H). For conformer 2:δ 2.19 (s, 3 H), 2.77 (t, J=5.9 Hz, 2 H), 3.81 (t, J=5.9 Hz, 2 H), 3.86 (s, 3 H), 3.87 (s, 3 H), 4.56 (s, 2 H), 6.59 (s, 1 H), 6.63 (s, 1 H).

Provenance & Evidence