Uracil-Thianthrenium Salts (Uracil-TT+BF4–) as a Coupling Partner in Sonogashira Cross-Coupling Reactions: Access to 5-Alkynyl Uracils and Synthetic Applications

Cross-coupling reactions are powerful tools for forging two different organic fragments via formation of C–C or C–heteroatom bonds. Herein, we for the first time synthesize a bench-stable cross-coupling reagent, uracil-TT+BF4–, for Sonogashira-type reaction to install an alkyne functionality selectively at position C-5 of uracils. A series of terminal alkynes were tolerated well, affording the desired products in good to excellent yields. Moreover, mild conditions, low catalyst loading, a broad substrate scope, and excellent functional group tolerance are some notable features of the current protocol. Furthermore, byproduct thianthrene (TT) formed in this reaction has been recovered and reused for making the uracil-TT+ reagent, highlighting the sustainability of the method.