C-alkylations of indoles and pyrroles with α-chloro sulfides on an alumina surface: a short synthesis of dithyreanitrile
Alumina-mediated C-alkylations of indoles and pyrroles with α-chloro sulfides have been examined. Thus, a mixture of indoles 1 and the α-chloro sulfides 2 or 3, on treatment with neutral alumina, gave the ethyl indol-3-ylacetates 5 and the corresponding acetonitriles 6, respectively. A similar reaction of the chloride 4 with 7-methoxyindole provided direct access to dithyreanitrile 7h, which is an insect antifeedant. The pyrrole 10 was also allowed to react with the α-chloro sulfides 2 and 3 to afford the 2-substituted products 11 and 12, respectively. On the other hand, the reactions of skatole 14 with 2 and 3 gave the 2-alkylation products 15 and 16, respectively, but in low yields. However, 2,3-dimethylindole 17 reacted smoothly with 2 and 3 to give the indolenines 18 and 19, respectively. The reaction of 2,5-dimethylpyrrole 25 with 2 afforded the 2,2,5-trisubstituted 2H-pyrrole 26 as a major product along with the 2,3,5-trisubstituted 1H-pyrrole 27. Some chemical transformations of the products 5, 18 and 26 are also described.