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.