[2+2+1] cyclization of allenes.

The [2+2+1] cyclization of an alkyne, an alkene and carbon monoxide, i.e., the Pauson-Khand reaction, is one of the most powerful tools for constructing a five-membered ring. In place of the alkene or alkyne part, the use of an allene functionality has proven to make this reaction more valuable for organic synthesis. This review focuses on the origin and progress of the allenic [2+2+1] cyclocarbonylation, including the chirality transfer of the allene and its synthetic applications.