The Baeyer–Drewson indigo synthesis (1882) is an organic reaction in which indigo is prepared from 2-nitrobenzaldehyde and acetone [1] [2]
The reaction is classified as a Aldol condensation. As a practical route to indigo, this method was displaced by routes from aniline.[3]
In the English literature this reaction is usually called Baeyer–Drewson reaction, although the author of the original paper was called Drewsen.