Allenecontaining

Allene-containing compounds are those that include the allene functional group, a cumulated diene with the connectivity C=C=C. The allene moiety consists of two orthogonal π bonds sharing a central carbon; as a result, the substituents at each end lie in perpendicular planes. When substituents on the two terminal carbons are different, allenes can be chiral, even without stereocenters, giving axial chirality.

Common examples include the parent allene (propadiene, CH2=C=CH2) and a wide range of substituted allenes such as 1,2-dialkyl- and aryl-substituted allenes. Substitution patterns influence stability and reactivity; highly substituted allenes can be isolable and serve as synthetic handles.

Synthesis methods include dehydrohalogenation of 1,3-dihaloalkenes, rearrangements of propargyl derivatives (such as the Fritsch–Buttenberg–Wiechell rearrangement), and transition-metal-catalyzed couplings that form the allene core from alkynes or vinyl precursors. Allene-containing motifs also arise via isomerization of propargyl halides, and from cyclopropenone ring openings in some cases.

Reactivity and applications: allenes participate in cycloadditions (including [4+2] and [2+2] variants), undergo allene–ene reactions, and serve as versatile building blocks in organic synthesis. In organometallic chemistry, allenes act as ligands or as components of metallacycles; their stereochemical richness enables enantioselective catalysis and the preparation of chiral natural products and pharmaceuticals.

Safety: many allenes and allene-containing compounds are reactive and may require careful handling; some may be lachrymatory or toxic and should be handled in appropriate facilities.