Abstract Both substituted 2, 4, 5, 6-tetrahydrocyclopenta [c] pyrazoles and 2, 4, 5, 6- tetrahydropyrrolo [3, 4-c] pyrazoles have been synthesized by the 3+ 2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.