Seven-Membered Rings

The synthesis of iboga alkaloids, containing an isoquinuclidine ring, fused with an indoloazepine ring system, has been reviewed. There continues to be strong interest in seven-membered heterocycles containing one, two, or three of the heteroatoms N, O, or S. The majority of the literature relates to aromatic fused systems containing at least one N and is driven by the search for new biologically active molecules. New synthetic methods of interest include transition metal-catalyzed, multicomponent, dipolar cycloaddition, ring expansion, and electrocyclization processes. There is increasing recognition that seven-membered rings are useful tools for restricting the conformation of bioactive compounds, and certain systems exhibit atropisomerism which in turn can affect their reactivity and biological activity.