Abstract
Treatment of pteridin-4(3H)-one (Ia) with aqueous methoxyamine solution at 70° and pH 6 gave 85% of 4,5-diaroinocopyrimidin-6(1H)-one (IIa) but at pH 7·5 gave none of the pyrimidine and 46% of methyl 3-(methoxyiminomethylamino)pyrazine-2-carbohydroxamate (VIIa). 6-Methylpteridin-4(3H)-one behaved similarly.Cyclisation of the pyrazine (VIIa), its 5- and 6-methyl- and its 5,6-dimethyl-derivatives (VIIb–d) gave 3-methoxypteridin-4(3H)-ones (VIa–d). These pteridines were also prepared by treating methyl 3-aminopyrazine-2-hydroxamates (VIIIa–d) with formic acid and acetic anhydride. Treatment of methyl 3-aminopyrazine-2-hydroxamates (VIIIa and d) with acetic acid and acetic anhydride gave 3-methoxy-2-methylpteridin-4(3H)-ones (VIe and f). The N-methoxypteridines were very readily cleaved by methoxyamine. 1 H N.m.r. spectra are recorded and the mechanisms of the ring-cleavage reactions are discussed.
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