Baeyer–Emmerling indole synthesis
The Baeyer–Emmerling indole synthesis is a method for synthesizing indole from a (substituted) ortho-nitrocinnamic acid and iron powder in strongly basic solution. This reaction was discovered by Adolf von Baeyer and A. Emmerling in 1869. 
The reaction of iron powder upon o-nitrocinnamic acid first yields a substituted hydroxylamine. The intermediate hydroxylamine then condenses with the 2nd carbon on the 1-position to yield indole-2-carboxylic acid, giving off H2O in the process. This carboxylic acid can be decarboxylated to yield indole.