Trifluoroacetic anhydride → 7-Methoxy-1H-isothiochromen-4(3H)-one

Participants

Reaction Steps

3-methoxybenzylmercaptoacetic acid from Step 2 (10.82 g) was dissolved in trifluoroacetic acid (50 mL). Trifluoroacetic acid anhydride (25 mL) was added and the reaction stirred under a nitrogen atmosphere for 0.25 hours. At this time, TLC showed no starting material. The solution was carefully poured into 10% Na2CO3 solution (500 mL) which was stirring vigorously. The organics were extracted into ether (500 mL) and washed with brine (300 mL), dried over MgSO4 and concentrated in vacuo. The resulting brown solid was purified by silica gel chromatography eluting with 20% ethyl acetate in hexane to yield 7-methoxyisothiochroman-4-one (4.84 g, 49%): 1H NMR (CDCl3) δ=3.48p (t, 2H, J=0.8 Hz), 3.83p (s, 3H), 3.84p (s, 2H), 6.6p (d, 1H, J=2.4 Hz), 6.83p (dd, 1H, J=2.4, 8.9 Hz), 8.0p (d, 1H, J=8.9 Hz).

Provenance & Evidence