Synthesis of isomeric triazolopyrrolopyrimidines

Abstract

4-Hydrazino-7H-pyrrolo[2,3-d]pyrimidines (4) were cyclocondensed with formic acid or triethyl orthoformate to give 7H-1,2,4-triazolo[1,5-c]pyrrolo[3,2-e]pyrimidines (5) and 7H-1,2,4-triazolo[4,3-c]pyrrolo-[3,2-e]pyrimidines (6) respectively. The [4,3-c]-isomers (6) were rearranged into thermodynamically more stable [1,5-c]-isomers (5). The identical compounds (5) were prepared using another route by reacting 3-amino-4-imino-7H-pyrrolo[2,3-d]pyrimidines (3) with formic acid or triethylorthoformate. Reaction of 2-amino-3-cyanopyrroles (1) with triethyl orthoformate followed by hydrazinolysis afforded (3) via the formation of N-ethoxymethylene-2-amino-3-cyanopyrroles (2).