Sulfonylation reactions photocatalyzed by quantum dots: rule of band-position and surface chemistry

An environmentally friendly methodology for the synthesis of different functionalized sulfones is described here. Quantum dots (QDs) of cysteamine (Cys) or 3-mercaptopropionic acid (MPA) capped cadmium chalcogenides (CdY, Y = S, Se, Te) were used as photocatalyst (UV, lambda = 365 nm) for sulfonylation reactions. The reaction between benzyl bromide and sodium p-toluenesulfinate was used to determine the ideal experimental conditions, where CdSe-Cys presented the best photocatalytic activity, and the sulfonylation product was isolated in 4% to 92% yields. The optimized reaction conditions were then applied on reactions of benzyl, allyl, alkyl, aryl halides and alpha-bromoesters using different sodium salts of sulfinic acids and the products where obtained in a 57% to 99% yield range after 2 to 8 hours. A mechanism proposal involves the simultaneous reduction/oxidation of the reagents by the exciton generated by photoexcitation of the QDs. The photocatalytic activity of the QDs was estimated by analysis of the conduction/valence band energies and correlated with LUMO/HOMO energies of the reagents. Cyclic voltammetry was used as an analytical tool.

Automated summary

This article describes an environmentally friendly method for synthesizing different functionalized sulfones. Quantum dots were used as photocatalysts for sulfonylation reactions. The optimized reaction conditions were applied to reactions of various compounds, yielding products in a range of 57% to 99% after 2 to 8 hours. The mechanism proposed involves the simultaneous reduction/oxidation of the reagents through the exciton generated by the photoexcitation of the quantum dots. The photocatalytic activity of the quantum dots was estimated and correlated with the energy levels of the reagents using cyclic voltammetry as an analytical tool.