Access to Pyrazolo[1,5-a]pyrimidinone Regioisomers from Acylated Meldrum's Acids

Two complementary and efficient methods for the regioselective synthesis of functionalized pyrazolo[1,5-a]pyrimidinones were developed from 3-aminopyrazoles and acylated Meldrum's acids. Fine-tuning the reaction conditions enables selective access to either pyrazolo[1,5-a]pyrimidin-5-ones or -7-ones in high yields. This protocol offers a reliable route to pyrazolo[1,5-a]pyrimidin-5-ones, a subclass with few reported syntheses, and highlights the value of acylated Meldrum's acids as building blocks for regioselective heterocycle synthesis and biologically relevant scaffold generation.