Site-selective C-H functionalization of sulfocoumarin and pyridine derivatives

Abstract

Part 1. Regioselective palladium(II)-catalyzed aerobic oxidative Heck-type C3 alkenylation of sulfocoumarins. An efficient method for the direct C-H olefination of sulfcoumarins with a wide range of alkenes is developed. Moreover, $O_2$ was successfully utilized as the sole oxidant for the oxidative Heck reaction. This approach enables the rapid generation of various 3-alkenylated sulfocumarins.

Part 2. Visible-light-induced remote C($sp^3$)-H pyridylation of sulfonamides and carboxamides. Visible-light-induced site-selective C($sp^3$)–H pyridylation of sulfonamides and carboxamides has been accomplished using N-amidopyridinium salts as both amido radical precursors and pyridine sources under metalfree, mild reaction conditions. The N-centered radicals generated by the single-electron reduction of Namidopyridinium substrates undergo selective 1,5-hydrogen atom transfer (HAT) to form alkyl radical intermediates. Remarkably, excellent C4-selectivity in radical trapping with pyridinium salts is observed for the generated primary, secondary, and tertiary alkyl radicals to ultimately provide synthetically valuable $\delta$-pyridyl sulfonamides and $\gamma$-pyridyl carboxamides. The utility of this powerful platform is further demonstrated by offering a practical approach for the late-stage functionalization of complex amide derivatives.