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

• Published in: European journal of organic chemistry 2024-10, Vol.27 (46), p.n/a
• Main Authors: García‐Manzano, Eibber J., Cuellar, Micaela A., Martín, Sandra E., Budén, María E., Barolo, Silvia M.
• Format: Article
• Language: English
• Subjects: Electron transfer; Heterocycles; Photoinduced cyclization; Sulfonamides; Visible light
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202400833

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: 4H‐benzo[e]pyrazolo[1,5‐b][1,2,4]thiadiazines and 5‐amino‐6‐thia‐4,5a‐diazaacephenanthrylenes. The synthetic strategy involved nucleophilic substitution reactions to prepare key sulfonamide starting substrates, followed by photoinduced cyclization (via the Substitution Radical Nucleophilic Unimolecular, SRN1) 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‐4,5a‐diazaphenanthrylenes. The synthesis of 4H‐Benzo[e]pyrazolo[1,5‐b][1,2,4]thiadiazines and 5‐Amino‐6‐thia‐4,5a‐diazaacephenanthrylenes derivatives by photoinduced intramolecular coupling from of 1‐((2‐halophenyl)sulfonyl)‐3‐alkyl‐1H‐pyrazol‐5‐amines and 1‐((2‐halophenyl)sulfonyl)‐1H‐benzo[d]imidazol‐2‐amines is presented. The synthetic protocol uses only KOtBu and DMSO to generate aryl radicals at room temperature. The reaction was explored with different substituents groups on the starting materials, demonstrating moderate to good products yields, with 13 examples and yields of up to 78 %.