Polysubstituted phenazines

Some time ago, Holliman and co-workers illustrated a method for synthesizing polysubstituted phenazines by reductive cyclization of o-nitrodiphenylamine. However, the yield was poor when competitive cyclizations occurred <70CC1423>. Recently, Kamikawa and co-workers reported a more efficient method to synthesize phenazines using sequential aniline arylation, which was first introduced by Buchwald <97JOC1264>. Regioselective bromination of o-nitrodiphenylamine 226 with bromine in the presence of sodium bicarbonate yielded 227 which was subjected to the Buchwald conditions to provide the desired phenazine 228 and the eliminated product 229 <00TL355>. The former compound is a proposed intermediate for the synthesis of the radical scavenger benthocyanin A. 

Naturally occurring phenazines have interesting biological activities but the available methods for their preparation offer only poor yields. T. Kamikawa et al. prepared polysubstituted phenazines by a new route involving two subsequent Pcf -catalyzed amlnations of aryl bromides using the conditions developed by Buchwald and Hartwig. ... 

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See also in sourсe #XX -- [ ]

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