Abstract:The regioselective condensation of hydrazines and ynone trifluoroborates provides access to a range of pyrazole 5-trifluoroborates. The stability of the borate unit allows chemoselective halogenation of the heteroaromatic ring, thereby delivering pyrazole scaffolds that allow orthogonal functionalization at C5 and C4. The modular reactivity of these intermediates is exemplified by crosscoupling reactions, enabling regiocontrolled synthesis of fully-functionalized pyrazole derivatives.
Ynone trifluoroborate salts undergo a base-promoted condensation reaction with alkylthiols to generate thiophene boronates with complete regiocontrol. The products are isolated in high yield and can be further derivatized through conventional C-B bond functionalization reactions.
We report a novel and general method to access a highly under‐studied privileged scaffold—pyrimidines bearing a trifluoroborate at C4, and highlight the broad utility of these intermediates in a rich array of downstream functionalization reactions. This chemistry is underpinned by the unique features of the trifluoroborate group; its robustness provides an opportunity to carry out chemoselective reactions at other positions on the pyrimidine while providing a pathway for elaboration at the C−B bond when suitably activated.
Small‐molecule heterocycles bearing orthogonal functionality have the potential to deliver diverse structural motifs that aid the drug‐discovery effort. This work highlights how a readily assembled N‐hydroxyethyl pyrazole trifluoroborate offers rapid access to architecturally distinct 5‐6‐6‐ and 5‐7‐6‐fused tricyclic compounds. This chemistry is not only amenable to single compound synthesis, but also to high‐throughput experimentation. It gives easy access to diverse compound arrays with various physicochemical and ADME profiles by fully automated library synthesis. The combination of the high‐throughput experimentation with rapid testing of the compounds in an integrated physicochemical and ADME profiling workflow allows accelerated design of novel lead compounds in drug‐discovery projects.
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