Dioxygen concentration-dependent selective hydroxysulfonylation of olefins by rose bengal-sensitized photocatalysis

The synthesis of beta-hydroxysulfones selectively in preference to beta-ketosulfones by dye-sensitized photocatalysis is demonstrated by employing inexpensive and readily available olefins and sulfonyl hydrazides/N-hydroxy sulfonamides in the presence of oxygen. The facile hydroxysulfonylation reaction, which involves the use of rose bengal (RB) as a photocatalyst and dioxygen as an oxidant, permits access selectively to secondary and tertiary beta-hydroxysulfones in good to excellent isolated yields at rt and is compatible with aryl, heteroaryl and alkyl sulfonyl hydrazides. Mechanistically, sulfonyl radicals are generated by a cascade of redox reactions, set off by the photocatalyst RB, between sulfonyl hydrazide and dioxygen. Attack of the sulfonyl radicals on olefins followed by oxygenation of the radical intermediates leads to hydroxysulfonylation products selectively without the requirement of a metal catalyst/additive/reductant/base, conforming to the tenets of sustainable chemistry. It is shown that the formations of beta-hydroxysulfones and beta-ketosulfones proceed concurrently through two different routes and that the outcome is crucially dependent on oxygen concentration with the former being formed predominantly under an oxygen atmosphere, a feature that is heretofore unprecedented to the best of our knowledge. A facile visible light-mediated synthesis of beta-hydroxysulfones selectively from olefins and sulfonyl hydrazides/N-hydroxy sulfonamides in the presence of rose bengal as a photocatalyst and dioxygen as an oxidant is described.

Automated summary

In this study, the synthesis of beta-hydroxysulfones instead of beta-ketosulfones was selectively demonstrated using dye-sensitized photocatalysis. The reaction utilized inexpensive and readily available olefins and sulfonyl hydrazides/N-hydroxy sulfonamides in the presence of oxygen. It was found that the hydroxysulfonylation reaction, which employed rose bengal as a photocatalyst and dioxygen as an oxidant, selectively produced secondary and tertiary beta-hydroxysulfones in good yields. The formation of beta-hydroxysulfones and beta-ketosulfones was shown to proceed through different routes depending on the concentration of oxygen.