5.7- Dioxo-1,2,4-triazolo pyrimidine

Heating the 8-amino-7-chloro-2-oxo-l,2,4-triazolo[l,5-c]pyrimidine 189 with hydrochloric acid caused hydrolysis of the chloro group yielding the 2,7-dioxo derivative 190 (68JOC530) (Scheme 72). 

R1 = R2 = H) gave the triazolo[l,5-a]pyrimidines (125), but with 124 (R1 = R2 = Me) afforded the dioxo derivative 126, and with a-cyano- y-butyrolactones (127) or 2-amino-3-ethoxycarbonyl-5,6-dihydro-4//-thiopyran (129) gave the triazolopyrimidines 128 and 130, respectively (81JHC1287). Treatment of 4-ethoxymethylene-2-phenyl-5(4//)-oxazolone (131) with 5-amino-3-methylthio-l//-1,2,4-triazoles gave the triazolo[l,5-a]pyrimidi-none 132 and the [4,3-a] isomer 133 (93H955) (Scheme 24). 

Table 6 Electrophilic reactions of 4,6-dimethyl-5,7-dioxo-l, 2,3-triazolo[4,5-<(]pyrimidine.

Figure 4.3.6 Structure of 4,5-dihydro-5-oxo-[l,2,4ltriazolo-[l,5a]pyrimidine (SHtpO), 4,7-dihydro-5-methyl-7-oxo-[l,2,4]triazolo-[l,5a]pyrimidine (HmtpO), and 4,5,6,7-tetrahydro-5,7-dioxo-[l,2,4]triazolo-[1,5a]pyrimidine (H2tp02)...

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