Anti-Markovnikov hydrochlorination and hydronitrooxylation of α-olefins via visible-light photocatalysis

Abstract

Conventional hydrofunctionalization of α-olefins with mineral acids proceeds with Markovnikov selectivity to afford branched isomers. The direct formation of linear constitutional isomers is challenging, yet anti-Markovnikov addition would be valuable for the synthesis of commodity chemicals, such as primary alcohols, which are currently only accessible via stoichiometric redox reactions, with a full equivalent of waste of both oxidant and reductant. Strategies that utilize radical intermediates have been demonstrated, but only for activated alkenes, and the direct use of aqueous mineral acids remains elusive. Here we present anti-Markovnikov addition reactions of aqueous hydrochloric and nitric acid to unactivated alkenes. The transformation is enabled by the in situ generation of photoredox-active ion pairs, derived from acridine and the mineral acid, as a combined charge- and phase-transfer catalyst. The introduction of a hydrogen atom transfer catalyst enabled us to bypass the challenging chain propagation by hydrochloric and nitric acids that originates from the high bond dissociation energy.

Electron-Transfer-Enabled Concerted Nucleophilic Fluorination of Azaarenes: Selective C–H Fluorination of Quinolines

“…The observation of 1-chlorododecane in an intermolecular radical-trapping experiment with 1-dodecene is consistent with the formation of Cl•. 38,49 According to an electrochemistry study, the additive Et 3 N•HCl (E p1/2 = +0.94 V vs SCE) cannot be oxidized by ground-state protonated quinoline (E p1/2 = −1.03 V vs SCE). However, the reduction of excited-state protonated quinoline (E 0−0 = 2.65 V, 50 E p1/2 * = +1.62 V vs SCE) by Et 3 N•HCl is feasible.…”

Radical Hydrocarboxylation of Unactivated Alkenes via Photocatalytic Formate Activation

“…Of particular note, an α-amino acid derivative was found to be compatible under the reaction conditions and could be transformed into the linear diacid product in high yield (13). Substrates bearing a variety of pendant heterocycles, including oxetanes (12), γ-lactones (14), piperidines (15,16), pyrans (17), and imidazoles (18), each underwent the desired transformation. Hydrocarboxylation proceeds smoothly across a series of sterically hindered substrates (11,12,(14)(15)(16)(17)19), which included fully substituted carbon centers in both cyclic (12) and acyclic systems (19).…”

“…Substrates bearing a variety of pendant heterocycles, including oxetanes (12), γ-lactones (14), piperidines (15,16), pyrans (17), and imidazoles (18), each underwent the desired transformation. Hydrocarboxylation proceeds smoothly across a series of sterically hindered substrates (11,12,(14)(15)(16)(17)19), which included fully substituted carbon centers in both cyclic (12) and acyclic systems (19). Moderate to high yields of the linear carboxylic acid products were obtained across a series of exocyclic and acyclic 1,1disubstituted alkene substrates upon gentle heating (20−22).…”

“…Alkene hydrofunctionalization methods that exploit radical intermediates are a fundamental class of synthetic reactions. Radical reactivity offers a complementary regio- and chemoselectivity profile relative to polar pathways. , Despite anti-Markovnikov hydrobromination dating back a century, , the development of radical hydrofunctionalization reactions remains a contemporary area of investigation. − Our group has a particular interest in alkene hydrocarboxylation using radical intermediates. , Carboxylic acids are a readily diversifiable functional handle − and are themselves a common motif found in natural products, pharmaceuticals, and commodity chemicals. − We envision that a broad and general radical hydrocarboxylation reaction would offer a powerful complement to transition-metal-catalyzed methods, such as the numerous established CO-based approaches − and the emerging alternative technologies that proceed through migratory insertion into CO 2 . − However, established approaches to radical hydrocarboxylation have remained largely limited to activated alkenes (Figure A). ,,− Unactivated aliphatic alkenes are an abundant and important substrate class but remain more challenging to engage due to their attenuated reactivity. Indeed, in the past year, Yu and co-workers reported the first and only synthetic methodology that engages unactivated alkenes with CO 2 •– .…”

Photoinduced FeCl3-Catalyzed Chlorination of Aromatic Sulfonyl Chloride via Extrusion of SO2 at Room Temperature

“…Nevertheless, the regioselective chlorination of electron-deficient arenes is even more challenging because of their weak nucleophilicity in comparison with the electron-rich arenes. Therefore, the development of convenient and efficient approaches to prepare aryl chlorides is of great significant . The organo sulfur compounds are stable, common, and cheap chemicals that are widely used in synthetic organic chemistry .…”