Simple preparation of 7-alkylamino-2-methylquinoline-5,8-diones: regiochemistry in nucleophilic substitution reactions of the 6- or 7-bromo-2-methylquinoline-5,8-dione with amines

7-Alkylamino-2-methylquinoline-5,8-diones () were prepared from 6-bromo-2-methylquinoline-5,8-dione () not from 7-bromo-2-methylquinoline-5,8-dione (). The chemistry of the transformation of 6-bromo-2-methylquinoline-5,8-dione () and various alkylamines, such as piperidine, 2-methylaziridine, benzylamine, n-butylamine, cyclohexylamine, t-butylamine, and ammonia, to 7-alkylamino compounds as well as the transformation of 7-bromo compound and the alkylamines to 6-alkylamino-2-methylquinoline-5,8-diones was studied. The efficient and simple synthetic routes of the key intermediates, 6- and 7-bromo-2-methylquinoline-5,8-diones ( and ), from 5,8-dihydroxy-2-methylquinoline () and 5,7-dibromo-8-hydroxy-2-methylquinoline (), respectively, were developed. We also proposed the mechanism for the unusual regioselectivity on the nucleophilic amination of 6- and 7-bromo-2-methylquinoline-5,8-diones ( and ).