Amino groups quinoxalines from

As might be expected from a consideration of electronic effects, an amino substituent activates pyrazines, quinoxalines and phenazines to electrophilic attack, usually at positions ortho and para to the amino group thus, bromination of 2-aminopyrazine with bromine in acetic acid yields 2-amino-3,5-dibromopyrazine (Scheme 29). 

Polymers containing heterocycles in the backbone include a variety of compounds, as the diversity of heterocyclic molecules is quite large. The polymers from this class may contain groups derived from furan, thiophene, pyrrole, isoindole, benzimidazole, benzothiazole, benzoxazole, quinoxaline, etc. Macromolecules with a ladder backbone containing, for example, a phenoxazine unit in their structure also are known. Amino thermosetting resins from melamine can be considered as polymers containing heterocycles in their structure. 

As seen from the retrosynthetic analysis of the strucmre presented below, the simplest and most accessible reagent for the synthesis of pyrrolo[ 1,2-a]quinoxalines is 1,2-DAB. If the aim is to synthesize a derivative of pyrrolo[l,2-a]quinoxaline from 1,2-DAB, the second reagent must be a compound with at least five carbon atoms having functional centers capable of reacting with the amino groups of the 1,2 DAB at positions 1, 2, and 5 (Fig. 3.6). 

Quinoxaline-2,3-diones 53, containing necessary substiments in the benzo moiety, are synthesized in three stages from o-halonitrobenzenes. The transformations involve the substimtion of an amino group for the halogen atom to form compounds 56, the reduction of the nitro group to the amino group and... 

The nitration of 6-methoxyquinoxaline in concentrated sulfuric acid at 0°C gives 6-methoxy-5-nitroquinoxaline. The position of the nitro group is confirmed by reduction of the product to 5-amino-6-methoxy-quinoxaline identical with a sample prepared from 2,3,4-triamino-anisole and glyoxal ... 

Corresponding electron-transport materials have been made by replacing the amino substituents in the first shell by oxadiazole groups (29) [70, 61] or phenyl-quinoxalines (30) [60]. As in the case of the amines, dendrimer-shaped structures are obtained by repeating the substitution pattern in a second shell (31) [76], The Tg was increased from 142°C in 29 to 222° C in 31. 

---