Unexpected regioselectivity in nitration of 3-aminoquinoxalin-2(1H)-ones

Regioselective nitration takes place at position 8 of 6,7-disubstituted-3-a minoquinoxalin-2(1H)-ones 3a-d. The orientation is not disturbed by the ele ctronic or steric effects of the substituents on the aromatic ring and on t he amino group. The isomeric 5-nitro derivative 9 is formed only in a round about way from 3,6,7-trichloroquinoxalin-2(1H)-one 7. When position 8 is oc cupied, the 5- nitro derivatives appear only as a minor component. The isom ers were identified by NMR techniques. Theoretical calculations (AM1, Hartr ee-Fock, B3LYP) and NMR investigations confirmed the presumed nitronium cat ion attack on the monoprotonated species 3ap.