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.

Facile preparation of polycyclic halogen-substituted 1,2,3-triazoles by using intramolecular Huisgen cycloaddition

“…In this study, the desired fused-ring triazole derivative 35 was obtained in a high yield by the Suzuki–Miyaura coupling reaction of 10 with o -nitrophenylboronic acid to nitroarene 34 , followed by treatment with triphenylphosphine. 25,26 Although pentacyclic product 35 did not fluoresce much in the solid state, it exhibited strong fluorescence in various organic solvents (Scheme 4 and Table 3).…”

Trends in carbazole synthesis – an update (2013–2023)

“…Classically, the synthesis of carbazoles relied on the Fischer–Borsche synthesis (condensation of cyclohexanone with phenylhydrazines), 21–23 the Graebe–Ullmann synthesis (thermolysis of 1-phenylbenzotriazole), 24 or the Cadogan–Sundberg synthesis (cyclisation of biarylnitrenes). 25,26 Such protocols, however, often require high reaction temperatures or suffer from low functional group tolerance, which with rising environmental consciousness in synthetic chemistry ( i.e. , Twelve Principles of Green Chemistry) 27–29 is no longer considered sustainable practice.…”

A π-extended tercarbazole-core multi-resonance delayed fluorescence emitter exhibiting efficient narrowband yellow electroluminescence

“…As outlined in Scheme 1, CzCzB was synthesized via a three-step reaction, using pinacolborate 1 15 as the starting material (details are available in the ESI†). The Pd-catalyzed Suzuki–Miyaura coupling of 1 with 1-bromo-2-nitrobenzene, followed by Cadogan cyclization using PPh 3 , 16 afforded 3 with a 9,1′:3′,9′′-tercarbazole core. Subsequently, the NaH-mediated nucleophilic substitution of 3 with iodomethane produced CzCzB in good yields.…”