Visible-light-driven Cadogan reaction

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

“…However, it was found that the molecules with electron‐deficient groups were more reactive than the molecules with electron‐donating substituents resulting in the requirement of prolonged reaction times. Additionally, the team performed the DFT calculations, which evidenced formation of the intermediate complex of nitrobiarenes and PPh 3 by an endergonic pathway [35] . Thus, this photoredox Cadogan reaction was proved to be very effective and beneficial by widening the substrate scope and producing a wide range of carbazoles with functional group tolerance.…”

“…[34] Zhonghua Qu, and research group discovered a mild metalfree visible-light-driven photochemical Cadogan-type cyclization and used it for the synthesis of differently substituted carbazoles (53, 55 and 57) as shown in Scheme 13. [35] Here, a wide variety of photocatalysts such as iridium and rutheniumbased complexes, organophotocatalysts e. g. Rose Bengal, Eosin Y, and an organic DÀ A type photosensitizer 4CzIPN (51) were screened as an initiative to improve the efficiency of this cyclization transformation. Interestingly, 51 was found to be an effective mediator for energy transfer from photons to the intermediate, enabling it to break the barriers of the ratedetermining step i. e. deoxygenation resulting in the formation of desired molecules in excellent yield.…”

“…Additionally, the team performed the DFT calculations, which evidenced formation of the intermediate complex of nitrobiarenes and PPh 3 by an endergonic pathway. [35] Thus, this photoredox Cadogan reaction was proved to be very effective and beneficial by widening the substrate scope and producing a wide range of carbazoles with functional group tolerance.…”

“…Various heterocycles (125) as shown in Scheme 28 were synthesized by Zhonghua et al through similar Cadogan conditions as used earlier for the generation of carbazole, indoles and indazoles. [35] Manna and colleagues, developed a metal-free, visible-light-and PPh 3 -mediated intermolecular reductive amination reaction, for the first time, between nitroarenes (126) and boronic acids (127) without using any photocatalyst as shown in Scheme 29. [21] Here, the nitroarenes acted as photosensitizers.…”

“…Zhonghua Qu, and research group discovered a mild metal‐free visible‐light‐driven photochemical Cadogan‐type cyclization and used it for the synthesis of differently substituted carbazoles ( 53 , 55 and 57 ) as shown in Scheme 13 [35] . Here, a wide variety of photocatalysts such as iridium and ruthenium‐based complexes, organophotocatalysts e. g. Rose Bengal, Eosin Y, and an organic D−A type photosensitizer 4CzIPN ( 51 ) were screened as an initiative to improve the efficiency of this cyclization transformation.…”