A Parallel Approach to 7-(Hetero)arylpyrazolo[1,5-a]pyrimidin-5-ones

A modular, two-pot assembly of 7-arylpyrazolo[1,5-a]pyrimidones from aryl/heteroaryl halides and aminopyrazoles in library format was developed. Sonogashira coupling of aryl bromides with triethyl orthopropiolate, followed by in situ orthoester hydrolysis, provides access to β-aryl ynoates, which undergo regioselective cyclocondensation with aminopyrazoles. The ability to vary the C7 vector of 7-arylpyrazolo[1,5-a]pyrimidones in two steps using readily available (hetero)aryl halides significantly enhances synthetic access to this challenging vector.