Annulation

Annulation (from Latin: anellus = small ring ), also condensation, in chemistry the term for the addition of another ring to one or more already existing rings of a cyclic molecule. In this case, at least two ring members (usually carbon atoms) at the same time part of two rings. In contrast, spiro compounds also contain at least two rings where only one ring member (usually a carbon atom) is part of two rings simultaneously.

The Anellierungs reactions include cyclizations, cycloadditions - [2 2 ] cycloaddition and the Diels -Alder reaction - condensation with maleic anhydride and the Robinson reaction.

Fused ring systems are often also called fused ring systems.

The spellings " annealing " and " annellation " are wrong, but common.