Gold-Catalyzed Three-Component Annulation: Efficient Synthesis of Highly Functionalized Dihydropyrazoles from Alkynes, Hydrazines, and Aldehydes or Ketones.

Polysubstituted dihydropyrazoles were directly obtained by a gold-catalyzed three-component annulation. This reaction consists of a Mannich-type coupling of alkynes with N,N′-disubstituted hydrazines and aldehydes/ketones followed by intramolecular hydroamination. Cascade cyclization using 1,2-dialkynylbenzene derivatives as the alkyne component was also performed producing fused tricyclic dihydropyrazoles in good yields.