A Minireview on the Scope of Cadogan Cyclization Reactions Leading to Diverse Azaheterocycles

Abstract From the last two decades, Cadogan cyclization reaction is considered as one of the best routes for the preparation of various azaheterocycles comprising carbazoles, indoles, coumarins, carbolines, pyrazoloquinoxalines, S,N‐heterotetracenes from the nitro‐based substrates by using a variety of tetravalent phosphorus‐based reagents. To date the majority of Cadogan reactions are found to be intramolecular reactions, however, interestingly, a case of intermolecular Cadogan reaction is also reported, resulting in the widening of the reaction scope for futuristic perspectives. We report the Cadogan cyclization reactions for the synthesis of azaheterocycles from 2018 to present according to multiple classes of chemical frameworks including its scope (FDA approved drugs), along with the possibilities and mechanistic developments for unexpected products.