The Madelung synthesis is a chemical reaction

Chemical reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

 that produces (substituted or unsubstituted) indoles by the intramolecular

Intramolecular

Intramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule, a property or phenomenon limited to the extent of a single molecule.- Examples :...

 cyclization of N-phenylamides using strong base at high temperature.

This method is essentially confined to the preparation of 2-alkinylindoles (not easily accessible through electrophile aromatic substitution) because of the vigorous reaction conditions.