Formic Acid → 3-Formamido-2-phenyl-benzo(b)thiophene

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Reaction Steps

Preparation of the starting product by reduction of the 3-formamido-2-phenyl-benzo(b)thiophene which can be isolated either by drying of the intermediate product formed from preparation of the 3-amino-2-phenyl-benzo(b)thiophene from the 2-phenyl-benzo(b)thiophen-3-ol produced as an intermediate product (described following Example 14) by heating for 1 hour the 3-amino-2-phenyl-benzo(b)thiophene with the same quantity of formic acid at 98 to 100%, followed by dissolving in water and drying. In both cases, 3-formamido-2-phenyl-benzo(b)thiophene is obtained in a quantitative yield: thin colourless needles, mp 185°-186° C. (benzene). 3.0 g (11.8 mmol) of this amide and 1.08 g (28.4 mmol) of LiAlH4 in 60 milliliters of absolute dioxan are refluxed with stirring for 30 minutes. Water is added to the cooled reaction mixture to decompose the excess LiAlH4 and, after the addition of approximately 100 milliliters of CH2Cl2, it is stirred for a further 15 minutes. After centrifuging with the addition of a filtration aid the organic phase is dried over K2CO3 and evaporated. The hydrochloride of the solution of the residue is precipitated in a little chloroform by the action of hydrochloric gas: 2.6 g (80% of theory). The hydrochloride of 3-methylamino-2-phenyl(b)thiophene, colourless crystals in ethanol-ether, decomposition from 198° C. (in sealed tube). From this salt the base is released by the action of ammonia: 3-methylamino- 2-phenyl -benzo(b)thiophene, yellow rods, mp 78°-79° C. (methanol).

Provenance & Evidence