Gold(I)-Catalyzed Ring Expansions of Unactivated Alkynylcyclopropanes to (<i>E</i>)-2-Alkylidenecyclobutanamines in the Presence of Sulfonamides

The ring expansion of cyclopropane derivatives provides a powerful method to construct synthetically useful four-membered carbocycles. Herein, a new type of gold(I)-catalyzed ring expansion of an unactivated alkynylcyclopropane/sulfonamide trapping strategy to (E)-2-alkylidenecyclobutanamines was described. The reaction tolerates a range of aryl and alkyl substituents with moderate to good yields.