Dimethylformamide → 6,7-Dichloro-2-formyl-5-hydroxybenzo[b]thiophene

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Reaction Steps

A solution of 8.7 g of 6,7-dichloro-5-hydroxybenzo[b]thiophene in 50 ml of anhydrous tetrahydrofuran is placed in a 250 ml 3-necked flask and cooled to -25°. To the solution under nitrogen, is added dropwise 42 ml of a solution of 2.5M n-butyllithium at a rate such that the temperature did not rise above -10°. After total addition, the mixture is stirred at 0°-5° for 3 hrs. To the mixture is added 14 ml of anhydrous dimethylformamide over a period of 20 mins. The reaction mixture is allowed to warm to room temperature and stirred for 1 hr. Quenching with 400 ml of 2N hydrochloric acid, followed by extraction with ethyl acetate, gives a precipitate. Recrystallization from acetone-hexane affords 6.5 g of 6,7-dichloro-2-formyl-5-hydroxy-benzo[b]thiophene, mp 197°-198°.

Provenance & Evidence