Radical Hydrocarboxylation of Unactivated Alkenes via Photocatalytic Formate Activation

Abstract

Herein we disclose a strategy to promote the hydrocarboxylation of unactivated alkenes using photochemical activation of formate salts. We illustrate that an alternative initiation mechanism circumvents the limitations of prior approaches and enables hydrocarboxylation of this challenging substrate class. Specifically, we found that accessing the requisite thiyl radical initiator without an exogenous chromophore eliminates major byproducts that have plagued attempts to exploit similar reactivity for unactivated alkene substrates. This redox-neutral method is technically simple to execute and effective across a broad range of alkene substrates. Feedstock alkenes, such as ethylene, are hydrocarboxylated at ambient temperature and pressure. A series of radical cyclization experiments indicate how the reactivity described in this report can be diverted by more complex radical processes.

Multicomponent hydrosulfonylation of alkynes for the synthesis of vinyl sulfones

“…On the basis of the above experimental results and the previous related reports, 16–18 a plausible mechanism for this transformation was derived, and is shown in Scheme 3. According to this mechanism, initially, the instability of aryl diazonium salts produces aryl radicals at room temperature, followed by in situ generation of aryl sulfonyl radicals I with the release of SO 2 from K 2 S 2 O 5 accompanied by the production of K 2 SO 3 .…”

“…16 Subsequently, the sulfonyl radical undergoes radical addition to the alkynes to produce the sulfonylated vinyl radical intermediate II , which then abstracts the hydrogen atom from 4-CF 3 C 6 H 4 SH to afford the final product 4 . 17 Also, two equivalents of thiyl radicals coupled together from two consecutive reactions were proposed to produce the disulfide by-product 8a , 18 which was isolated and characterized using nuclear magnetic resonance (NMR) spectroscopy.…”

Recent Advances in Reactions Involving Carbon Dioxide Radical Anion

“…Very recently, Wickens’ group further expanded the substrate scope to unactivated alkenes. Notably, the requisite thiyl radical was generated from thiols under 427 nm LEDs irradiation without external photocatalyst …”

“…Notably, the requisite thiyl radical was generated from thiols under 427 nm LEDs irradiation without external photocatalyst. 49 In 2021, Li and co-workers developed a photoredox activation of formate salts for hydrocarboxylation of alkenens in an additive-free fashion (Scheme 32). 50 With the formate salt as the carboxyl source, reductant, and HAT reagent, a variety of alkenes could be converted into valuable acid products under blue light irradiation.…”

Visible Light‐Driven, Persulfate‐Mediated Hydrocarboxylation of Vinylsulfones

“…As such, Wickens and co-workers developed a photocatalytic, thiolmediated formate delivery (Scheme 1, A); [20] which could be later also applied for unactivated alkene substrates. [21] Meanwhile, Huang et al (Scheme 1, B), [22] as well as Mita and co-workers (Scheme 1, C) [23] developed photocatalytic hydrocarboxylation processes via direct or indirect HAT, respectively.…”