Vilsmeier–Haack reactions of α-hydroxyketenedithioacetals: a facile synthesis of substituted pyridines

The reaction of α-hydroxyketenedithioacetals, generated by the 1,2-addition of methyl Grignard reagent to α-oxoketenedithioacetals, with the Vilsmeier reagent was investigated. The reaction proceeds with acid-catalysed dehydration to afford sulphur substituted 1,3-butadienes, which undergo subsequent iminoalkylations. The intermediate iminium salts formed were successfully transformed into 2-methylsulfanyl substituted 4-aryl pyridines, in the presence of ammonium acetate