2-Phenylquinoxaline 4-oxide reactions

The reactions of 2-phenylquinoxaline 4-oxide (193) with Grignard reagents give two main products, e.g., 2,3-diphenylquinoxaline (195)... 

Hayashi and his co-workers investigated the reactions of 2-substituted quinoxaline 4-oxides with ketones.210-212 2-Phenylquinoxaline 4-oxide (193) yields 2-phenyl-3-phenacylquinoxaline 4-oxide (203) with acetophenone and sodamide. However, 2-cyanoquinoxaline 4-oxide under these conditions yields cu-(3,4-dihydro-3-oxo-2-quinoxalinyl)aceto-phenone (204) by displacement of the cyano group by the ketone carbanion and rearrangement of the N-oxide.212... 

Quinoxaline 1,4-dioxide undergoes reaction with acetyl chloride and substitution occurs in the benzene ring to give 6-chloroquinoxaline 1 -oxide and, on increasing the reaction time, 3-chloroquinoxaline 1-oxide and 6,7-dichloroquinoxaline appear as additional products.A similar reaction is observed with 3-phenylquinoxalin-2(l//)-one 4-oxide and its 7-substituted derivatives, where ring substitution at position 6 again is accompanied by deoxygenation. 2-Chloroquinoxalinc 1-oxide (19) is obtained in 60% yield by treatment of quinoxaline 1,4-dioxide with benzenesulfony chloride and consequent neutralization of the benzenesulfonate initially formed,and in addition about 3% of 3-chloroquinoxaline 1-oxide is formed. 

Both quinoxaline 1-oxide and 2-phenylquinoxaline 4-oxide give anilinoquinoxalines (36) on reaction with phenyl isocyanate. With excess... 

Reaction of 3,4-dihydro-3-oxo-2-phenylquinoxaline 1-oxides 8 with acetic anhydride in the presence of perchloric acid at room temperature gives high yields (80-96%) of the yellow to red N-acetoxyquinoxalinium perchlorates 9. The salts (R = H or MeO R = Me) decompose rapidly at room temperature, but the remaining quinoxalinium salts are relatively stable. ... 

A plausible reaction mechanism for the formation of quinoxaline derivatives from 1,2-DAB and phenacyl bromide is illustrated in Scheme 2.19. Initially, a nucleophilic substitution occurs on the phenacyl bromide to afford the intermediate 217. Intermediate 217 spontaneously cychses to form 3-phenyl-1,2-dihydroquinoxaline 218, which imdergoes aromatization under air oxidation to afford 2-phenylquinoxaline 214a as the final product. 

---