2-methyl-3-ethoxycarbonyl-4-hydroxythiophene in the vilsmeier reaction

Continuing our investigation of the properties of 2-methyl-3-ethoxycarbonyl-4-hydroxythiophene (I) 1], we found that it readily undergoes electrophilic substitution reactions. We studied the behavior of I under the conditions of the Vilsmeier reaction. The structures of the reaction products depend on the temperature conditions: at 30–35°C, 2-methyl-3-ethoxycarbonyl-4-hydroxy-5-formylthiophene (H) is formed in 74% yield while 2-methyl-3-ethoxycarbonyl-4-chloro-5-formylthiophene (III) is formed in 50% yield at 100°. The reaction of I with dimethylbenzamide and phosphorus oxychloride gives 2-methyl-3-ethoxycarbonyl-4-hydroxy-5-benzoylthiophene (IV) in 41% yield.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, p. 427, March, 1972.