Acetaldehyde → 6,7-Dichloro-5-hydroxy-alpha-methylbenzo[b]thiophene-2-methanol

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Reaction Steps

To a solution of 25 g of 6,7-dichloro-5-hydroxybenzo[b]thiophene in 145 ml of dried tetrahydrofuran at -25° to -30° is added 110 ml of 2.5M n-butyllithium maintaining a temperature below -21°. After the addition, the carbon tetrachloride-dry ice bath is replaced with an ice-water bath and the mixture is stirred at 0°-5° for 4 hrs. A solution of 7.5 ml of freshly distilled acetaldehyde in 10 ml tetrahydrofuran is added dropwise. An additional 2 ml of acetaldehyde is added and the solution is stirred for 1 hr. The solution is poured onto 500 ml of a cold 5% hydrochloric acid solution and the mixture is extracted with ethyl ether. The ether extracts are washed, dried over anhydrous magnesium sulfate, filtered and solvent is removed to give a solid. Recrystallization from ethyl acetate and hexane gives 20 g of 6,7-dichloro-5-hydroxy-α-methylbenzo[b]thiophene-2-methanol, mp 173°-174°.

Provenance & Evidence