Synthesis of 3‐Arylazoindoles through Iron(III)‐Catalyzed C−H Azolation of Indoles and Arylhydrazines

• Published in: Advanced synthesis & catalysis Vol. 366; no. 9; pp. 2123 - 2129
• Main Authors: Li, Kun, Zhang, Jin‐Qi, Liao, Wei‐Cong, Liang, Cui, Ma, Xiao‐Pan, Mo, Dong‐Liang, Chen, Chun‐Hua
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 21.05.2024; Wiley Subscription Services, Inc
• Subjects: 2-Substituted indoles; 3-Arylazoindoles; Arylhydrazines; Chemistry; Chemistry, Applied; Chemistry, Organic; Column chromatography; C−H Azolation; Functional groups; Hydrogen; Indoles; Iron; Iron(III)-catalyzed; Physical Sciences; Reagents; Recrystallization; Science & Technology; Substrates; FUNCTIONALIZATION; AZO; Iron(III)-catalyzed; PHOTOSWITCHES; COMPLEXES; 2-Substituted indoles; CHEMISTRY; 3-Arylazoindoles; Arylhydrazines; CATALYST; C-H Azolation; AROMATIC-AMINES
• ISSN: 1615-4150; 1615-4169
• DOI: 10.1002/adsc.202301388

A variety of functionalized 3‐arylazoindoles were prepared in good to excellent yields through an iron(III)‐catalyzed C−H azolation of 2‐substituted indoles with arylhydrazines under mild reaction conditions. The reaction underwent an initial TBN‐mediated nitrosation, 1,5‐hydrogen migration, intramolecular condensation, and 1,5‐hydrogen migration over four steps in one pot. A paracyclophane‐derived 3‐phenylazoindole could be prepared in 25% yield over three steps and some prepared 3‐arylazoindoles showed a different fluorescence emission wavelength and existed obvious pH conditions response. The present method highlights broad substrate scope of easily available starting materials, wide range of functional group compatibility, gram scalable preparations, high atom economy, avoidance of unstable and explosive azolation reagents, and simple purification operations by extraction, washing, and recrystallization without flash column chromatography.