Unusual Cu(I)-catalyzed 1,3-dipolar cycloaddition of acetylenic amides: formation of bistriazoles

C-carbamoyl-1,2,3-triazoles have recently attracted much interest due to their potent biological activity. While synthesizing C-carbamoyl-1,2,3-triazoles by the copper(I)-catalyzed 1,3-dipolar cycloaddition of organic azides 1 and acetylenic amides 2, we found that the expected 1,2,3-triazole products 3 were obtained as the only products in excellent yields when CuSO₄ and sodium ascorbate were used as the Cu(I)-catalyst. Surprisingly, the unexpected bistriazole products 4 were one of the major products obtained along with the 1,2,3-triazoles 3 when using a direct Cu(I)-catalyst such as CuI or CuBr.