Palladium-catalyzed addition of alkynes to cyclopropenes: an entry to stereodefined alkynylcyclopropanes.

The Herrmann−Beller (H−B) phosphapalladacycle catalyzed the addition of terminal alkynes to unsymmetrical gem-disubstituted cyclopropenes to give alkynylcyclopropanes as single diastereomers in good to excellent yields. The stereofacial discrimination at the approach of the bulky alkynylpalladium species is believed responsible for the diastereoselectivity control of the addition reaction.