[OH-].[K+].[CH3:3]S(C)=O.[OH:7][C:8]1[C:18]([OH:19])=[CH:17][C:11]2[S:12][C:13]([C:15]#[N:16])=[CH:14][C:10]=2[CH:9]=1.ICI>ClCCl.O>[O:7]1[C:8]2[CH:9]=[C:10]3[CH:14]=[C:13]([C:15]#[N:16])[S:12][C:11]3=[CH:17][C:18]=2[O:19][CH2:3]1A mixture of powdered potassium hydroxide (12.36 g) and dimethylsulphoxide (100 ml) was stirred at room temperature for 5 min. then treated with 5,6 -dihydroxy-benzo[b]thiophene-2-carbonitrile (5.26 g). After 1 minute di-iodomethane (4.4 ml) was added and the suspension was stirred at room temperature for 75 minutes, then more di-iodomethane (2.2 ml) was added. After a further 30 minutes the reaction was poured into water (500 ml) and extracted with ethyl acetate (2×100 ml). The organic extracts were combined, washed with 2MHCl and saturated brine, then dried and evaporated to give a brown crystalline residue. The crude product was suspended in hot dichloromethane (200 ml), filtered, and the filtrate was passed through a column of silica gel (0.2-0.5 mm, Merck, 25 g). The appropriate fractions were combined and evaporated to dryness to give a white solid (3.4 g). Crystallisation from acetone/ether afforded pure thieno[2,3-f]-1,3-benzodioxole-6-carbonitrile, m.p. 179°-180° C.
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