C‐N and N‐N bond formation via Reductive Cyclization: Progress in Cadogan /Cadogan‐Sundberg Reactionǂ

Abstract Cadogan/Cadogan‐Sundberg cyclization reaction has been reported as one of the most efficient routes for the synthesis of a wide variety of N ‐heterocycles from the easily accessible starting materials such as o ‐nitrobiaryls or o ‐nitroarenes, o ‐nitrostyrenes by treating with tetravalent phosphorus compounds (trialkyl or triaryl phosphines or trialkyl phosphites). The reaction has been successfully employed in Carbon‐Carbon as well as Carbon‐Nitrogen bond formation for the scaffolds like carbazole, indoles, coumarins, and indazoles. To the best of authors’ knowledge, the present review is the first compilation of the literature from almost two decades (2000 to present) on Cadogan/Cadogan‐Sundberg cyclization reaction, its scope, mechanistic aspects, and limitations.