Propanal → 6,7-Dichloro-5-hydroxy-alpha-ethylbenzo[b]thiophene-2-methanol

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Reaction Steps

A solution of 7.0 g of 6,7-dichloro-5-hydroxybenzo[b]thiophene in 50 ml of dry tetrahydrofuran is cooled to -30°, using a dry ice-carbon tetrachloride bath and to the mixture is added dropwise, 35 ml of 2.2M n-butyllithium in hexane while the temperature is maintained below -20°. Following the addition, the bath is replaced with an ice-water bath and the reaction is stirred for 4 hrs at a temperature of 0°-5°. To the mixture is added dropwise solution of 3 ml of freshly distilled propionaldehyde in 5 ml of tetrahydrofuran. The bath is removed. The reaction mixture is stirred for 20 minutes and poured onto cold 10% hydrochloric acid. The mixture is extracted 3 times with ethyl ether. The combined ether extracts are washed, dried and the solvent is removed to give a solid. Recrystallization from ethyl ether and hexane gives 5.9 g of 6,7-dichloro-5-hydroxy-α-ethylbenzo[b]thiophene-2-methanol, mp 145°-145.5°.

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