Acetic Acid → (benzo[b]thiophen-5-yl)-2,5-dimethyl-1H-pyrrole

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A stirred solution of benzo[b]thiophen-5-amine (2.48 g, 17.0 mmol), hexane-2,5-dione (1.95 mL, 17.0 mmol) and glacial acetic acid (0.2 mL) in benzene (35 mL) was heated to reflux under a Dean-Stark head. After 14 h the reaction was cooled to r.t., diluted with diethyl ether (40 mL), and successively washed with aqueous 2 N hydrochloric acid (30 mL), brine (30 mL), a saturated aqueous solution of sodium hydrogen carbonate (30 mL) and finally brine (30 mL). The organic layer was separated, dried over magnesium sulfate, filtered and the solvent evaporated in vacuo to yield 1-(benzo[b]thiophen-5-yl)-2,5-dimethyl-1H-pyrrole (3.67 g, 97%) as a light orange crystalline solid. 1H NMR δ (CDCl3, 400 MHz) 2.04 (s, 6 H), 5.93 (s, 2 H), 7.19 (dd, J=8, 2 Hz, 1 H), 7.37 (d, J=5 Hz, 1 H), 7.55 (d, J=5 Hz, 1 H), 7.66 (d, J=2 Hz, 1 H), 7.94 (d, J=9 Hz, 1 H).

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