Oxidative amination and hydroxylation of 1,3,7-triazapyrenes in aqueous medium

Abstract

We have already reported the unusual capacity of 1,3,7-triazapyrenes 1a and 1b [1] and 7-alkyl-1,3,7-triazapyrenium salts [2][3][4][5] to react readily in aqueous solution with O-nucleophilic reagents to give mono-and disubstitution products. This is the result clearly not only of the -electron deficiency of these compounds but also the specific peri-fusion structure of this heterocyclic system.The oxidative amination of the most electrophilic heterocycles such as naphthyridines [6] or 1,2,4-triazine [7] is carried out by action of a solution of KMnO 4 in liquid ammonia. We have discovered, however, that 1,3,7-triazapyrenes 1a and 1b may be aminated in a solution of ammonia in aqueous dioxane in the presence of K 3 [Fe(CN) 6 ]. The reaction proceeds at 50-55°C to give 6-amino-1,3,7-triazapyrene (2a) in 95% yield and 6-amino-2-methyl-1,3,7-triazapyrene (2b) in 89% yield. N N N R N H 2 N N N R N N N H R O 1a,b 2a,b NH 3 , K 3 [Fe(CN) 6 ] H 2 O -dioxane, 50-55°C 3a,b HCl/H 2 O, room temperature K 3 [Fe(CN) 6 ] 1-3 a R = H, b R = MeThe amination also proceeds in the absence of dioxane as the cosolvent but requires a greater reaction time and the reaction products are formed in reduced yield, i.e., dioxane is necessary to increase the solubility of bases 1a,b. This is apparently the first example of the oxidative amination of heterocycles in aqueous medium.

Ureas as new nucleophilic reagents for SNH amination and carbamoyl amination reactions in the 1,3,7-triazapyrene series

“…15 In our previous reports, we have shown that 1,3,7-triazapyrene (1a) displays special properties due to the unique fusion of the carbocyclic and heterocyclic rings. These properties include an unusual ease of oxidative nucleophilic substitution of hydrogen, such as hydroxylation, 21 and even amidation. 28 Another unusual feature of 1,3,7-triazapyrenes is that the greater part of these transformations can be carried out in aqueous media.…”