Visible-Light-Promoted C–H Selenylation of Pyrazolo[1,5-a]pyrimidines

This study presents a visible-light-promoted regioselective C–H selenylation method for the synthesis of selenylated pyrazolo[1,5-a]pyrimidines. The researchers employed erythrosine B as a photocatalyst and optimized the reaction conditions to achieve high yields. The methodology demonstrated broad substrate scope and regioselectivity, and gram-scale synthesis was also feasible.

Facts

• Visible-light-promoted C–H functionalization is an attractive strategy for direct conversion of C–H bonds to C–C and C–heteroatom bonds.
• Organoselenides are useful organic molecules with applications in pharmaceuticals, catalysis, and material science.
• The synthesis of organoselenides through C–H functionalization is an important strategy.
• Pyrazolo[1,5-a]pyrimidine derivatives are nitrogen-containing fused heterocycles found in various biologically and pharmaceutically important molecules.
• Synthesis of functionalized pyrazolo[1,5-a]pyrimidine derivatives has attracted synthetic chemists.
• Previous methodologies for the synthesis of pyrazolo[1,5-a]pyrimidines did not extensively explore selenylation of the scaffold.
• Erythrosine B is an organic dye with less explored photocatalytic applications compared to other dyes.
• Researchers developed a visible-light-promoted C–H selenylation method using erythrosine B as the photocatalyst.
• Optimization of reaction conditions led to the use of MeOH as the solvent, 3 mol % erythrosine B as the photocatalyst, and an oxygen atmosphere under white LED irradiation.
• The methodology demonstrated high efficiency and regioselectivity in the selenylation of various pyrazolo[1,5-a]pyrimidine derivatives and diselenides.
• The protocol was also applicable for the selenylation of other electron-rich heterocycles.
• Gram-scale synthesis of selenylated pyrazolo[1,5-a]pyrimidines was successfully achieved.

Visible-light-promoted C–H selenylation is a valuable strategy for the direct synthesis of selenylated pyrazolo[1,5-a]pyrimidines. In this study, the researchers utilized erythrosine B as a photocatalyst and optimized the reaction conditions to achieve efficient selenylation at the 3-position of pyrazolo[1,5-a]pyrimidine derivatives. The use of a white LED as the light source allowed for the regioselective formation of selenylated products. The methodology demonstrated a broad substrate scope, including various pyrazolo[1,5-a]pyrimidine derivatives with different substituents and electron-rich heterocycles. The yields were generally good to excellent. Additionally, the researchers successfully performed gram-scale synthesis, showcasing the practical applicability of the method. Controlled experiments using radical scavengers suggested a radical-mediated mechanistic pathway for the transformation.

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The authors aimed to develop a methodology for the extensive selenylation of pyrazolo[1,5-a]pyrimidines, an important scaffold for various biologically active and pharmaceutically important molecules. They utilized visible-light photocatalysis with erythrosine B as the photocatalyst under white LED irradiation. The optimized conditions involved MeOH as the solvent, 3 mol % erythrosine B as the photocatalyst, and an oxygen atmosphere. The methodology exhibited good yields and high regioselectivity for various pyrazolo[1,5-a]pyrimidine derivatives and different diselenides. The authors also demonstrated the gram-scale synthesis of the selenylated products. Controlled experiments indicated that the reaction proceeded via a radical pathway. This work expands the scope of visible-light-promoted C–H functionalization and provides a useful strategy for the synthesis of selenylated pyrazolo[1,5-a]pyrimidines.

In this study, the researchers focused on the development of a visible-light-enabled methodology for C–H selenylation, aiming to synthesize organoselenides efficiently. Pyrazolo[1,5-a]pyrimidine derivatives were chosen as the target scaffold due to their importance in various biological and pharmaceutically relevant molecules. 

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Overall, this study provides an efficient and regioselective approach for the synthesis of selenylated pyrazolo[1,5-a]pyrimidines using visible-light photocatalysis.

Visible-Light-Mediated Regioselective C3–H Selenylation of Pyrazolo[1,5-a]pyrimidines Using Erythrosine B as Photocatalyst

The Journal of Organic Chemistry