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

Abstract

Regioselective nitration takes place at position 8 of 6,7-disubstituted-3-aminoquinoxalin-2(1H)-ones 3a–d. The orientation is not disturbed by the electronic or steric effects of the substituents on the aromatic ring and on the amino group. The isomeric 5-nitro derivative 9 is formed only in a roundabout way from 3,6,7-trichloroquinoxalin-2(1H)-one 7. When position 8 is occupied, the 5-nitro derivatives appear only as a minor component. The isomers were identified by NMR techniques. Theoretical calculations (AM1, Hartree–Fock, B3LYP) and NMR investigations confirmed the presumed nitronium cation attack on the monoprotonated species 3ap.