Intramolecular addition of aryl radicals to the azo-group; synthesis and properties of N-(carbazol-9-yl)phenylaminyl radicals

Abstract

2′-(Phenylazo)biphenyl-2-yl radicals (3; Ar = Ph), produced by reduction of 2′-(phenylazo)biphenyl-2-diazonium tetrafluoroborate (6) with potassium iodide at –20 °C, undergo intramolecular 1,5-addition to the azo-group, affording N-(carbazol-9-yl)phenylaminyl radicals (4; Ar = Ph), from which 1,2-dicarbazol-9-yl-1,2-diphenylhydrazine (8) is formed by N,N-coupling. The hydrazine (8) is thermally unstable and easily fragments at room temperature into aminyl radicals (4; Ar = Ph), which appear to undergo hydrogen abstraction and C,N-coupling as the major reaction paths.