With Nitriles or Imidates

Higher amides, as well as the nitriles, are poorly represented as reagents for converting o-amino esters to annelated pyrimidines. At least methyl anthranilate and ethyl cyanoformate (not usually a reactive chemical) formed a good yield of 2-ethoxycarbonylquinazolin-4-one (140) when heated at 120°C with hydrogen chloride in acetic acid.325 

Benzyl thioacetimidate and 4-amino-2-ethoxycarbonylpyrazole, in boiling pyridine, gave a quantitative yield of 5-methylpyrazolo[4,3-d]pyrimidin-7-one (see 17).329 

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The reactivity of 5-amidinoisothiazoles (221) was explored to demonstrate the equilibrium 221 222 (Scheme 37). However, on reacting with nitriles or imidates, 5-amino compounds 220 (R = Me, Ph) give directly the rearranged thiadiazoles 222. The equilibrium between the two heterocycles (in different solvents at room temperature) is not observed, and this result is attributed to the greater stability of the 1,2,4-thiadiazole... 

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