Seven-Membered Rings

New synthetic methods to prepare seven-membered heterocyclic compounds containing one or more of the heteroatoms N, O, or S are covered. Aromatic systems containing at least one N atom were the focus of many reports. Research was often driven by the search for new bioactive heterocycles for use in medicinal chemistry and for the synthesis of natural products. Notable synthetic methods included transition metal-catalyzed, cycloaddition, ring-expansion, cascade-type, and C-H functionalization processes. A number of reviews in the field were also published