Ce. Muller, FORMATION OF 7,9-DISUBSTITUTED XANTHINIUM COMPOUNDS UNDER MILD CONDITIONS BY ALKYLATION OF SILYLATED XANTHINES, Synthetic communications, 24(9), 1994, pp. 1311-1315
Silylated, 3-unsubstituted xanthine derivatives afford 7,9-diallyl and
7,9-dibenzylxanthinium compounds upon the reaction with excess 2-prop
enyl (allyl) or benzyl bromide at room temperature.