A metal-free strategy, alternative to the known complex cycloaddition reactions, towards 2-carboxylated thieno [2,3-b] indole derivatives has been successfully developed. The novel approach involves as starting materials easy accessible 1,2-diaza-1,3-dienes and indoline 2-thione and requires mild reaction conditions. Furthermore, the easy work-up required makes this method amenable for a one-pot approach as demonstrated in the preparation of thienodolin, a natural product isolated from Streptomyces albogriseolus that exhibits valuable biological properties.