Synthesis of phenazines from ortho-bromo azo compounds via sequential Buchwald-Hartwig amination under micellar conditions and acid promoted cyclization. Issue 46 (12th November 2020)

• Record Type: Journal Article
• Authors: Yousif, Dawod; Monti, Mauro; Papagni, Antonio; Vaghi, Luca
• Is Part Of: Tetrahedron letters. Volume 61:Issue 46(2020)
• Publication Date: 2020-11-12
• Subjects: Phenazines -- Azobenzenes -- Micellar synthesis -- Buchwald-Hartwig amination -- Electrocyclization; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tetlet.2020.152511
• Languages: English
• ISSNs: 0040-4039

Abstract

Graphical abstract: Highlights: Phenazines are obtained via tandem amination\cyclization of ortho -bromo azobenzenes. The micellar B-H step is achieved in water without the need of inert atmosphere. Ortho -bromo azobenzenes are prepared by selective bromination or diazo coupling. Abstract: Non-symmetric phenazines were synthesized via the Buchwald-Hartwig amination of ortho -bromoazobenzenes with anilines under micellar conditions, using the commercially available surfactant Kolliphor EL in water, followed by an acid-promoted 6π-electrocyclization-aromatization process. Two different synthetic pathways to obtain the ortho -bromo azo intermediates were explored, namely the palladium catalysed selective ortho bromination of azobenzenes and the diazo coupling of ortho -bromo diazonium salts with N, N -dimethylaniline, imidazole, phenol, sodium methanesulfinate and ethyl chloroformate.