Synthesis of 3-benzylxanthine and Lumazine Analogues

Several xanthines (7–13) are prepared by the cyclisation of 1-benzyl-5,6-diaminouracil with single-carbon inserting agents such as aromatic aldehydes, formamides, acetic anhydride, carbon disulfide, and nitrous acid. Treatment of 6-amino-1-benzyl-5-nitrosouracil with anilinobenzylidene derivatives (14–18) affords 7-hydroxyxanthines (19–23). Cyclisation of the diaminouracil 3 with glyoxal, benzil, and diethyl oxalate leads to lumazines (25–28).