Synthesis of 2-substituted-6,7-dimethoxy- and 6,7,8-trimethoxy-3-hydroxyquinolin-4(1H)-ones

Acetonyl and phenacyl esters of 4,5-dimethoxy- and 3,4,5-trimethoxyanthrani lic acids 3 were prepared by reduction of corresponding nitro derivatives 2 . Acetonyl 4,5-dimethoxyanthranilate (3a) was prepared by reaction of 4,5-d imethoxyanthranilic acid and chloroacetone. Cyclization of these acetonyl a nd phenacyl esters in polyphosphoric acid provided the corresponding 2-subs tituted-6,7-dimethoxy- and 6,7,8-trimethoxy-3-hydroxyquinolin-4(1H)-ones 4. A new method of the thermal cyclization is also described. The structure o f the prepared compounds was confirmed by H-1 NMR spectroscopy.