Carbothiolation of Styrenes by Visible‐Light‐Induced Thiyl Radicals: C3‐Functionalization of Benzofuran‐2(3H)‐ones

Abstract

Thiyl radicals by far have taken part in manifold natural processes with regard to biochemistry. Utilizing their capability of reversibly adding onto carbon‐carbon double bond may be able to create valuable transformations. Herein, we report a novel thiyl radical precursor that can release sulfur‐centered radical by irradiation of visible light under mild conditions (without metals, photocatalysts, and other additives). A series of sulfur‐containing 3,3‐disubstituted benzofuran‐2(3H)‐ones were obtained with good functional group tolerance by thiol‐ene addition of styrenes with thiyl radicals. Mechanistic study confirmed the proposed process driven by EDA (Electron Donor‐Acceptor) complex.

Recent Advances in Visible‐Light‐Driven C−S Bond Formation

“…Zheng and co‐workers described the visible‐light‐promoted three‐component carbothiolation of styrenes ( 16.1 Scheme 16), N ‐Hydroxyphthalimide (NHPI) propionates 16.2 (as the thiyl radical precursor) and benzofuranones 16.3 , delivering sulfur‐containing 3,3‐disubstituted benzofuran‐2(3H)‐ones 16.4 in high efficiency (Scheme 16). [54] …”

“…[53] Zheng and coworkers described the visible-light-promoted threecomponent carbothiolation of styrenes (16.1 Scheme 16), N-Hydroxyphthalimide (NHPI) propionates 16.2 (as the thiyl radical precursor) and benzofuranones 16.3, delivering sulfur-containing 3,3-disubstituted benzofuran-2(3H)-ones 16.4 in high efficiency (Scheme 16). [54] Csp 2 À S bond formation Allenes are privileged building blocks for the construction of regio-and diastereoselective complex compounds via variety of late-stage transformation such as cycloisomerization, cycloaddition and cross-coupling reactions. [55] Gryko and co-workers presented a visible light promoted Doyle-Kirmse reaction involving dizaoalkanes (17.1, Scheme 17) and propargyl sulfides 17.2, furnishing differently substituted allenes 17.3 a-d in good yields under mild conditions.…”

Photoinduced Vicinal 1,2-Difunctionalization of Olefins for the Synthesis of Alkyl Sulfonamides

“…Methods for direct carbothiolation of olefins are extremely limited, with only one reference found for functionalization of benzofuranone moieties. 16 Compared to previously described methods, the goal at the outset of the research described herein was to provide a facile method using previously established radical/polar crossover (RPC) manifolds for difunctionalization of olefins 17 leading to alkyl sulfonamides with unprecedented levels of complexity owing to the introduction of another substituent in a 1,2-vicinal fashion (Scheme 1C).…”

“…More recently, photochemical methods have been developed wherein olefins can be directly hydrosulfamoylated to furnish alkyl sulfonamide products (Scheme B). − Although these new, photochemical methods have great merit, thus far these methods have been limited to introduction of a hydrogen atom as the second coupling partner, leading to monofunctionalized products. Methods for direct carbothiolation of olefins are extremely limited, with only one reference found for functionalization of benzofuranone moieties . Compared to previously described methods, the goal at the outset of the research described herein was to provide a facile method using previously established radical/polar crossover (RPC) manifolds for difunctionalization of olefins leading to alkyl sulfonamides with unprecedented levels of complexity owing to the introduction of another substituent in a 1,2-vicinal fashion (Scheme C).…”