Vilsmeier reaction on 6-methylpurine

Application of the Vilsmeier formylation reaction to 6-methylpurine (I) gave purine-6-malonaldehyde (III), which could be oxidized to purine-6-carboxylic acid (IV), brominated to 6-tribromomethylpurine (V), and hydrolysed to hypoxanthine (VI). Treatment of the reaction mixture of 6-methylpurine (I), dimethylformamide, and phosphoryl chloride with hydrazine, phenylhydrazine, thiosemicarbazide, and hydroxylamine afforded, respectively, 6-(pyrazol-4-yl)-(VII), 6-(1-phenylpyrazol-4-yl)(VIII), 6-(1-thiocarbamolypyrazol-4-yl)(IX), and 6-(isoxazol-4-yl)-purine (X). Similar treatment of compound (I) with the Vilsmeier reagent and aniline produced the monoanil (XIV) of the dialdehyde (III); use of p-bromoaniline yielded a mixture of mono- and bis-p-bromoanils, (XV) and (XVI). Compound (X) gave 8-hydroxypurine-6-carboxylic acid (XI) on oxidation, and purine-6-malonaldehydonitrile (XIII) when heated in dimethyl sulphoxide. The structure of the anil (XV) is discussed in the light of X-ray diffraction studies.