REGIOSELECTIVE N- AND 0-ALKYLATION OF 3H-l,2,3TRIAZOLQ-4,5-dPYRIMIDINE-5,7(4H,6H)-DIONES (8-AZAXANTHINES) AND TRANSFORMATION OF 3-ALKYL DERIVATIVES INTO 1-ALKYL ISOMERS

摘要

The alkylation on the pyrimidine ring of 3-methyl-3H-l,2,31triazolo4,5-Hpyrimidine-5,7(4H,6H)-diones (1) with an equimolecular amount of alkylating agent in the presence of anhydrous potassium carbonate in aprotic solvents under heating took place only at the 4-position. The similar alkylation on the triazole ring of 6-methyl-lH- 1,2,3 triazolo4,5-dpyrimidine-5,7(4H,6W)-diones (4) with an equivalent alkylating reagent happened simultaneously at the 1- and 2-positions with the priority at the 2-position, On the other hand, the alkylation of 3,6-disubstituted derivatives (12a-d) at room temperature led to the 5-O-alkylation (14a-e) accompanied with the 4-N-alkylation (3a, 13a-d), but at high temperature only the 4-N-alkylation occurred The 3,4,6-tri-substituted derivatives (3a, 13d) underwent transformation with excess alkylating agents at high temperature leading to the formation of 1,4,6-tri-substituted derivatives (7, 15) with elimination of the 3-substituent in the same manner as xanthine.