A range of allenes are now readily available, including optically active ones with central and/or axial chirality. The corresponding cyclization reactions in the presence of organic halides and other types of unsaturated structures with differing steric and electronic character provide access to cyclic skeletons that were previously difficult to prepare.

Scheme 1. Transition metal-catalyzed cyclization reactions of allenes (part I)

Scheme 2. Transition metal-catalyzed cyclization reactions of allenes (part II)

Scheme 3. Pd(II)-catalyzed cyclization reactions of allenoic acids.

Scheme 4. Nucleophilic addition/cyclizations

Scheme 5. Electrophilic addition/cyclizations