Pteridines, CXVI. (1) Synthesis and Reactivity of 6-Substituted l,3-Dimethyl-7-hydroxylumazines and 7-Substituted l,3-Dimethyl-(5H)-lumazin-6-ones

6-Substituted 1,3-dimethyl-7-hydroxylumazines (5-7) have been synthesized from 1,3-dimethyluracil-5,6- diamine (1) and a-ketoacid esters (2-4) under weakly acidic conditions. The isomeric 7-substituted 1,3-dimethyllumazin- 6-ones (18-20) resulted from a regioselective Boon synthesis starting from 6-chloro-l,3-dimethyl-5- nitrouracil (8) and α-aminoacid esters (9-11) in a three-step procedure. H 2 0 2 oxidations led with 6 and 7 to the corresponding 5-N-oxides (21, 22) whereas in the lumazin-6-onc scries only the 7-phenyl derivative (20) reacted also at N-5 position forming a cyclic hydroxamic acid (23). The newly synthesized compounds have been characterized by elemental analyses, 1 H-NMR and UV spectra based upon pK a -determinations.