Synthesis of Trisubstituted Pyrroles from Rhodium-Catalyzed Alkyne Head-to-Tail Dimerization and Subsequent Gold-Catalyzed Cyclization

Dimerization of N-protected propargylic amines in a rather rare head-to-tail mode has been achieved under mild conditions with high selectivity using rhodium catalysts. The N-protecting group could be a sulfonyl, carbamate, or carbonyl functionality and (cyclooctadiene)rhodium chloride dimer/1,1'-bis(diphenylphosphino)ferrocene {[Rh(COD)Cl](2)/dppf} as well as tris(triphenylphosphine)rhodium chloride [Rh(PPh3)(3)Cl] proved to be active catalysts. In addition, these functionalized gem-enynes subsequently undergo selective gold(III)-catalyzed intramolecular hydroamination to give trisubstituted pyrroles under mild conditions.