Sundberg indole synthesis

What is Sundberg indole synthesis?

The origin of Sundberg indole synthesis can be traced back to the pioneering work of Smith in 1951. He developed a method for synthesizing carbazoles by subjecting o-azido biphenyl to pyrolysis or photolysis, and by thermolysis of o-(α-thienyl)-phenyl azide to obtain 4-thieno[3,2-b]indole, as well as α- and β-(o-azidophenyl)-pyridine to α- and γ-carbolines, respectively.

Sundberg indole synthesis - general reaction scheme
Sundberg indole synthesis

In 1972, Sundberg adapted this reaction for the synthesis of indole derivatives by subjecting o-azido styrenes to pyrolysis. As a result, the Sundberg indole synthesis refers to the thermolysis of o-azidostyrenes to produce indoles through a nitrene intermediate (also known as azene, imene, etc.).