A Facile Cycloisomerization for the Formation of Medium and Large Rings via Allenes

The use of allenes as proelectrophiles in Pd-catalyzed reaction provides a facile entry to macrocarbocycles, macrolactones, and macrolactams. Remarkably, medium-sized rings, notoriously the most difficult to generate, are produced in excellent yields, even in preference to the more easily formed ring sizes when both are feasible (see example below).