Gold-catalyzed ring enlargement and cycloisomerization of alkynylamide tethered alkylidenecyclopropanes

Alkynylamide tethered alkylidenecyclopropanes 1 undergo gold(i)-catalyzed ring enlargement and cycloisomerization to yield two kinds of heterocyclic polycyclic products 2 and 3 in moderate to good yields depending on the use of different gold(i) catalysts. The use of PPh3AuCl/AgOTf as the catalyst afforded ring enlarged polycyclic products 2 and the use of JohnphosAuCl/NaBARF as the catalyst furnished ring enlarged spiropolycyclic products 3via a further intramolecular Friedel-Crafts reaction. A plausible reaction mechanism has also been proposed on the basis of previous literature. Moreover, a useful transformation of ring enlarged spiropolycyclic products 3 to a ring enlarged polycyclic product 4 has also been presented.