The 1,4-reduction of aromatic compounds to the corresponding unconjugated cyclohexadienes by alkali metals dissolved in liquid ammonia in the presence of an alcohol is called Birch reduction. The reaction proceeds via a one-electron transition mechanism.
The cycloaddition of a conjugated diene and an alkene leads to a cycloalkene. In this reaction, participating bonds are broken and new bonds are simultaneously formed .
Cyclooctatetraene or cyclodeca-1,5-diene, for example, can be synthesized using specific metal catalysts.
Conjugated double-bond systems can be cyclized in a reversible reaction either by heating or using photolysis.