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.