2-Triazolylpyrimido[1,2,3-cd]purine-8,10-diones via 1,3-dipolar cycloadditions to 2-ethynylpyrimido[1,2,3-cd]purine-8,10-dione

This paper presents the synthesis of a series of 5,6-dihydro-4H,8H-pyrimido [1,2,3-cd]purine-8,10(9H)dione ring system derivatives with a [1,2,3]triazo le ring bonded in position 2. The procedure is based on cycloaddition of su bstituted alkyl azides to the terminal triple bond of 5,6-dihydro-2-ethynyl -9-methyl-4H,8H-pyrimido[1,2,3-cd]purine-8,10(9H)-dione (4). This cycloaddi tion produced two regioisomers - 5,6-dihydro-9-methyl-2-(1-substituted-1H-[ 1,2,3]triazol-5-yl)-4H,8H-pyrimido[ 1,2,3-cd]purine-8,10(9H)-dione (7) and 2-(1-substituted-1H-[1,2,3]triazol-4-yl) derivative 8. The required 2-ethyn yl derivative 4 was obtained from the starting 2-unsubstituted compound 1 b y bromination to yield the 2-bromo derivative 2, which was converted by Son ogashira reaction to trimethylsilylethyne 3 and finally, the protective tri methylsilyl group was removed by hydrolysis.