Electrophilic acetylation and formylation of pyrrolo[1,2-a]pyrazines: Substituent effects on regioselectivity

Described herein is electrophilic acetylation and formylation of pyrrolo[1,2-a]pyrazines with substituent(s) at C1 and/or C3 position(s) where substituents around the core skeleton allowed regiodivergent access to C6- or C8-acetylpyrrolo[1,2-a]pyrazines. While acetylation of pyrrolo[1,2-a]pyrazines (R(1) = H and R(3) = aryl or methyl) mainly gave rise to C8-acetylated products, acetylation with pyrrolo[1,2-a]pyrazines (R(1) = methyl and R(2) = aryl or methyl) provided C6-acetylated compounds as major products. In contrast, Vilsmeier-Haack formylation of pyrrolo[1,2-a]pyrazines took place at C6 position irrespective of the substituents at C1 and/or C3 site(s).