Assembly of conjugated enynes and substituted indoles via CuI/amino acid-catalyzed coupling of 1-alkynes with vinyl iodides and 2-bromotrifluoroacetanilides

摘要

Cross-coupling of 1-alkynes with vinyl iodides occurs at 80 degrees C in dioxane catalyzed by CuI/N,N-dimethylglycine to afford conjugated enynes in good to excellent yields. Heating a mixture of 2-bromotrifluoroacetanilide, 1-alkyne, 2 mol % of CuI, 6 mol % of L-proline, and K2CO3 in DMF at 80 degrees C leads to the formation of the corresponding indole. This conversion involves a CuI/L-proline-catalyzed coupling between aryl bromide and the 1-alkyne followed by a CuI-mediated cyclization process. An ortho-substituent effect directed by NHCOCF3 enables the reaction to proceed under these mild conditions. Both aryl acetylenes and O-protected propargyl alcohol can be applied, leading to 5-, 6-, or 7-substituted 2-aryl and protected 2-hydroxymethyl indoles in good yields. With simple aliphatic alkynes, however, lower yields were observed.