Synthesis and interconversion of isomeric pyrrolotriazolopyrimidines^†

4-Hydrazino-7H-pyrrolo[2,3-d]pyrimidines 4 were cyclocondensed with formic acid or triethyl orthoformate to give 7H-pyrrolo[3,2-e][1,2,4]triazolo[1,5-c]pyrimidines 6 and 7H-pyrrolo[3,2-e][1,2,4]triazolo[4,3-c]pyrimidines 7, respectively. The [4,3-c] isomers 7 were rearranged into thermodynamically more stable [1,5-c] isomers 6. The identical compounds 6 were prepared using another route by reacting 3-amino-4-imino-7H-pyrrolo[2,3-d]pyrimidines 3 with formic acid or triethyl orthoformate. The reaction of 2-amino-3-cyanopyrroles 1 with triethyl orthoformate gave N-ethoxymethylene-2-amino-3-cyanopyrroles 2. Further reaction with an equivalent of hydrazine hydrate provided 3-amino-4-imino-7H-pyrrolo[2,3-d]pyrimidines 3, whereas treatment with excess of hydrazine hydrate, 3 rearranged to 4-hydrazino-7H-pyrrolo[2,3-d]pyrimidines 4. Compounds 4 were also obtained by the treatment of N-ethoxymethylene-2-amino-3-cyanopyrroles 2 in excess of hydrazine hydrate. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:265–273, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20295