An Approach for the Synthesis of Pyrazolo[1,5-a]pyrimidines via Cu(II)-Catalyzed [3+3] Annulation of Saturated Ketones with Aminopyrazoles

A one-step synthesis of diversely substituted pyrazolo[1,5-a]pyrimidines from saturated ketones and 3-aminopyrazoles is presented. This transformation involves the in situ formation of α,β-unsaturated ketones via a radical process, followed by [3+3] annulation with 3-aminopyrazoles in one pot. Mechanistic studies have shown that the dual C(sp3)-H bond functionalization of inactive ketones is required for the formation of the title compounds. Notably, this dehydrogenative coupling process provides access to a host of functionalized pyrazolo[1,5-a]pyrimidines with antitumor potential from commercially available substrates.