Pteridines. Part XLII. Synthesis and properties of 8‐substituted 2,4‐dithiolumazines

Condensation reactions of the 5‐amino‐6‐(subst. amino)‐2,4‐dithiouracils 12 and 13 with diacetyl or benzil led to the 6,7,8‐trisubstituted 2,4‐dithiolumazines 14–16. Methylation of these compounds affected both thio functions forming various types of 2,4‐bis(methylthio)lumazine derivatives depending on the nature of the substituents at C(7) and N(8). The 6,7,8‐trimethyl‐2,4‐dithiolumazine (14) was converted into 7,8‐dihydro‐6,8‐dimethyl–7‐methylidene‐2,4‐bis(methylthio)pteridine (17), whereas the 8‐methyl‐6,7‐diphenyl‐(15) and the 8‐(2‐hydroxyethyl)‐6,7‐diphenyl‐2,4‐dithiolumazine (16) yielded the corresponding covalent inter‐ or intramolecular 7,8‐adducts 18–21. The unusual structures were proven by spectroscopic means and those of the alcohol adducts 20 and 21, furthermore, confirmed by X‐ray analysis.