反应详情

The intermediate N'-(4-chloro-3-cyano-5-formyl-2-thienyl)-N,N-dimethylformamidine (IV) ##STR4## is formed from the 4-hydroxythiophene derivative (III) by treatment with a mixture of N,N-dimethylformamide and phosphoryl chloride and then converted direct to 2-amino-4-chloro-3-cyano-5-formylthiophene by acid hydrolysis, without its having been isolated. For this it is expedient to dissolve the 4-hydroxythiophene derivative (III) in N,N-dimethylformamide and add phosphoryl chloride to the solution at a temperature of from 20° C. to 80° C.; the mole ratio of the hydroxythiophene to N,N-dimethylformamide to phosphoryl chloride is generally from 1:10:2 to 1:20:3. After a further period of from 2 h to 8 h, during which the solution is kept stirred at a temperature of from 20° C. to 80° C., the formamidine (IV) that is formed is subjected to acid hydrolysis, which is done conveniently by running the reaction mixture into water. After completion of the latter procedure (which is accompanied by a strongly exothermic reaction) the mixture is usually stirred at a temperature of from 80° C. to 100° C. for from 1 h to 4 h, during which time the required thiophene derivative (II) precipitates. The product is finally separated, washed, and dried.

1. customhaving been isolated
2. waitAfter a further period of from 2 h to 8 h