Photoinduced Intramolecular C−N Coupling For The Synthesis Of Azolo[1,2,4]Benzothiadiazines Derivatives

Abstract This paper explores an original synthesis of novel heterocyclic compounds derived from photoinduced intramolecular coupling reactions, involving the formation of C−N and C−C bonds. Specifically, two classes of compounds were targeted: 4 H ‐benzo[ e ]pyrazolo[1,5‐ b ][1,2,4]thiadiazines and 5‐amino‐6‐thia‐4,5 a ‐diazaacephenanthrylenes. The synthetic strategy involved nucleophilic substitution reactions to prepare key sulfonamide starting substrates, followed by photoinduced cyclization (via the Substitution Radical Nucleophilic Unimolecular, S RN 1) under mild conditions using visible light. The scope of the reaction was explored with different substituent groups on the starting materials, which demonstrated moderate to very good product yields, with 13 examples and yields of up to 78 %. Moreover, this strategy represents the first synthetic approach to obtain 5‐amino‐6‐thia‐4,5 a ‐diazaphenanthrylenes.