Internuclear cyclisation. Part XXII. Catalysed decomposition of diazonium fluoroborates from alkoxy-N-alkyl-2-aminobenzanilides

Abstract

Copper-catalysed decomposition of dry diazonium fluoroborates from alkoxy-N-alkyl-2-aminobenzanilides affords several new reactions not found in the thermal, uncatalysed decompositions. The products include benzanilides, phenanthridones, spiro-cyclohexa-dienones and -dienols, an azoxy-compound, and unsaturated dimeric products.

Formation of the dienones and dienol, where an extra oxygen atom has become incorporated, and the unsaturated dimers, can only be explained, simply, in terms of a free-radical mechanism. The initially formed aryl radical adds intramolecularly to the other benzene ring to give a stabilised cyclohexadienyl radical which can react with dissolved oxygen or dimerise. Clear evidence is thus provided for the participation of radicals in these catalysed diazonium decompositions.

Base-catalysed aromatisations of the cyclohexadienol to a biphenyl, and the unsaturated dimer (XVII) to a p-quaterphenyl are also described.