2,3-Annulated indoles exhibit a broad spectrum of biological activities. Various annulation
strategies are applied to generate these scaffolds from prefunctionalized aniline
or indole derivatives. Only a few methodologies allow the direct annulation of indole
itself, often associated with regioselectivity issues or restrictions on available
substitution patterns. More recently, ruthenium-catalyzed cascade transformations
of readily available propargyl alcohols have been applied to the selective synthesis
of various cyclo[b]fused indoles directly from indole. These efficient processes provide rapid access
to intricate molecular structures from simple starting materials and facilitate the
preparation of drug-like molecules.
Key words
annulation - carbazoles - cascade reactions - drug discovery - heterocycles - homogeneous
catalysis - indoles
