Bromination of quinolin-2(1H)-ones fluorinated on the benzene moiety

Abstract

Bromination of ten known fluorinated quinolin-2(1H)-ones by the KBrO₃/HBr system is investigated. If there is no F atom in the position 6 of substrate, the Br atom is introduced into position 3 or 6 to form monobromo derivative, the second Br atom is introduced into the same positions leading to 3,6-dibromo product. If a F atom is in position 6, the 3-bromo product is initially obtained, which gives a 3,5-dibromo or 3,8-dibromo derivatives upon further bromination depending on the F atoms positions. In this case, when both positions 5 and 8 of 3-bromoquinolin-2(1H)-one are unsubstituted, the second Br atom is introduced into position 8. If there are more than two F atoms in the benzene moiety, the sole 3-bromo product is obtained. Relative (ΔE) energies of the considered σ−complexes estimated by DFT calculations for the reactions in question are consistent with the experimentally observed regioselectivity.