Synthesis of Polysubstituted Pyrroles by Condensation of Acetylenes and Amines

Significance

Reported is a facile, highly efficient, one-pot synthesis of polysubstituted pyrroles from a 2:1 condensation of alkynes and amines. The addition-oxidative cyclization of alkynes 1 with amine 2 in the presence of AgBF₄ (catalyst) and phenyl iodo diacetate (PIDA, oxidant) gives pyrroles 3. The scope of this reaction has been explored in particular with various amines (aromatic bearing EDG/EWG and aliphatic). Although the reaction is tolerant in positional ArNH₂ substitution, it is quite sensitive to the electronic contribution for aromatic amines bearing EWGs. Significantly, a crossed alkynoate 4 and 5/benzylamine 6 condensation has been achieved to afford the unsymmetrical pyrroles 7. A plausible mechanism involving activation of the alkyne by silver(I) and nitreni-um ion generation by PIDA was proposed.