Cycloisomerization of 1,6‐Dienes Mediated by Lewis Super Acids without Additives: Easy Access to Polysubstituted Six‐Membered Carbocycles

The tin salt Sn(NTf2)4 (Tf=trifluoromethanesulfonyl) is an efficient catalyst for the selective and ring-size-specific cycloisomerization of highly substituted 1,6-dienes to give six-membered-ring carbocycles (see scheme; X=C(CO2Et)2, C(CO2Me)2 C(CN)(CO2Et), etc.). This is the first Lewis acid catalyzed cycloisomerization of this type of substrate.