Overcoming protic-solvent limitations in dithiane chemistry: photocatalyzed Giese addition and one-pot ketone synthesis

Abstract

Dithiane umpolung chemistry provides access to valuable acyl anion synthons; however, its reliance on strong bases, low temperatures, and the inherent instability of dithiane anions toward water and alcohols severely limit its practical sustainability. To address these challenges, we developed a visible-light-driven radical approach utilizing readily available trimethylsilyl-substituted dithianes as robust radical precursors. Single-electron oxidation generates an α-dithianyl radical that undergoes efficient Giese-type conjugate addition to a broad array of electron-deficient alkenes. The resulting adducts are directly converted into ketones through a sub-stoichiometric iodine-mediated oxidative dethioacetalization, enabling a concise one-pot sequence. This transformation proceeds smoothly in green protic media, such as ethanol–water mixtures, obviating the need for harsh reagents or specialized equipment. Notably, the quantitative sustainability of this protocol is underscored by a significantly enhanced atom economy (AE) of up to 37.7% and a more than four-fold improvement in reaction mass efficiency (RME) compared to conventional two-step methods. Overall, the method provides an operationally simple and sustainable route to ketones from bench-stable precursors, effectively overcoming the long-standing limitations of classical anionic dithiane chemistry.