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N-Arylphenothiazines as strong donors for photoredox catalysis - pushing the frontiers of nucleophilic addition of alcohols to alkenes.

ABSTRACT: A new range of N-phenylphenothiazine derivatives was synthesized as potential photoredox catalysts to broaden the substrate scope for the nucleophilic addition of methanol to styrenes through photoredox catalysis. These N-phenylphenothiazines differ by their electron-donating and electron-withdrawing substituents at the phenyl group, covering both, ? and ?-type groups, in order to modulate their absorbance and electrochemical characteristics. Among the synthesized compounds, alkylaminylated N-phenylphenothiazines were identified to be highly suitable for photoredox catalysis. The dialkylamino substituents of these N-phenylphenothiazines shift the estimated excited state reduction potential up to -3.0 V (vs SCE). These highly reducing properties allow the addition of methanol to ?-methylstyrene as less-activated substrate for this type of reaction. Without the help of an additive, the reaction conditions were optimized to achieve a quantitative yield for the Markovnivkov-type addition product after 20 h of irradiation.

SUBMITTER: Speck F

PROVIDER: S-EPMC6334793 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Oxydifluoromethylation of Alkenes by Photoredox Catalysis: Simple Synthesis of CF2H-Containing Alcohols.

Project description:We have developed a novel and simple protocol for the direct incorporation of a difluoromethyl (CF2 H) group into alkenes by visible-light-driven photoredox catalysis. The use of fac-[Ir(ppy)3] (ppy=2-pyridylphenyl) photocatalyst and shelf-stable Hu's reagent, N-tosyl-S-difluoromethyl-S-phenylsulfoximine, as a CF2 H source is the key to success. The well-designed photoredox system achieves synthesis of not only ?-CF2 H-substituted alcohols but also ethers and an ester from alkenes through solvolytic processes. The present method allows a single-step and regioselective formation of C(sp(3))-CF2 H and C(sp(3))-O bonds from C=C moiety in alkenes, such as hydroxydifluoromethylation, regardless of terminal or internal alkenes. Moreover, this methodology tolerates a variety of functional groups.

| S-EPMC4737308 | biostudies-literature

?-Selective Aroylation of Activated Alkenes by Photoredox Catalysis.

Project description:Late-stage synthesis of ?,?-unsaturated aryl ketones remains an unmet challenge in organic synthesis. Reported herein is a photocatalytic non-chain-radical aroyl chlorination of alkenes by a 1,3-chlorine atom shift to form ?-chloroketones as masked enones that liberate the desired enones upon workup. This strategy suppresses side reactions of the enone products. The reaction tolerates a wide array of functional groups and complex molecules including derivatives of peptides, sugars, natural products, nucleosides, and marketed drugs. Notably, addition of 2,6-di-tert-butyl-4-methyl-pyridine enhances the quantum yield and efficiency of the cross-coupling reaction. Experimental and computational studies suggest a mechanism involving PCET, formation and reaction of an ?-chloro-?-hydroxy benzyl radical, and 1,3-chlorine atom shift.

| S-EPMC6527503 | biostudies-literature

Metal-free defluorinative arylation of trifluoromethyl alkenes via photoredox catalysis.

Project description:Literature methods to access gem-difluoroalkenes are largely limited to harsh, organometallic-based methods, and known photoredox-mediated processes are not amenable to aryl radical addition to trifluoromethyl alkenes. A metal-free, functional group-tolerant method for the preparation of benzylic gem-difluoroalkenes is described. Halogen atom abstraction from (hetero)aryl halides generates aryl radicals that undergo a defluorinative arylation of ?-trifluoromethyl alkenes, tolerating electronically disparate aryl radicals and ?-trifluoromethyl alkenes.

| S-EPMC7210470 | biostudies-literature

Visible-light photoredox catalysis enabled bromination of phenols and alkenes.

Project description:A mild and efficient methodology for the bromination of phenols and alkenes has been developed utilizing visible light-induced photoredox catalysis. The bromine was generated in situ from the oxidation of Br(-) by Ru(bpy)3 (3+), both of which resulted from the oxidative quenching process.

| S-EPMC3999835 | biostudies-literature

Nucleophilic Aromatic Substitution of Unactivated Fluoroarenes Enabled by Organic Photoredox Catalysis.

Project description:Nucleophilic aromatic substitution (SNAr) is a classical reaction with well-known reactivity toward electron-poor fluoroarenes. However, electron-neutral and electron-rich fluoro(hetero)arenes are considerably underrepresented. Herein, we present a method for the nucleophilic defluorination of unactivated fluoroarenes enabled by cation radical-accelerated nucleophilic aromatic substitution. The use of organic photoredox catalysis renders this method operationally simple under mild conditions and is amenable to various nucleophile classes, including azoles, amines, and carboxylic acids. Select fluorinated heterocycles can be functionalized using this method. In addition, the late-stage functionalization of pharmaceuticals is also presented. Computational studies demonstrate that the site selectivity of the reaction is dictated by arene electronics.

| S-EPMC7720250 | biostudies-literature

Intermolecular oxidative amination of unactivated alkenes by dual photoredox and copper catalysis.

Project description:Oxidative amination of alkenes via amidyl radical addition is potentially an efficient method to generate allylic amines, which are versatile synthetic intermediates to bioactive compounds and organic materials. Here by combining photochemical generation of amidyl radicals with Cu-mediated β-H elimination of alkyl radicals, we have developed an intermolecular oxidative amination of unactivated alkenes. The reaction relies on tandem photoredox and copper catalysis, and works for both terminal and internal alkenes. The radical nature of the reaction and the mild conditions lead to high functional group tolerance.

| S-EPMC8179295 | biostudies-literature

Enantioselective Amino- and Oxycyanation of Alkenes via Organic Photoredox and Copper Catalysis.

Project description:The β-amino nitrile moiety and its derivatives frequently appear in natural product synthesis, in drug design, and as ligands in asymmetric catalysis. Herein, we describe a direct route to these complex motifs through the amino- and oxycyanation of olefins utilizing an acridinium photooxidant in conjunction with copper catalysis. The transformation can be rendered asymmetric by using a serine-derived bisoxazoline ligand. Mechanistic studies implicate olefin-first oxidation. The scope of amines for the aminocyanation reaction has been greatly expanded by undergoing a cation radical intermediate as opposed to previous N-centered radical-initiated aminocyanations. Furthermore, alkyl carboxylic acids were included as nucleophiles in this type of transformation for the first time without any decarboxylative side reactions.

| S-EPMC10962007 | biostudies-literature

Direct C-H trifluoromethylation of di- and trisubstituted alkenes by photoredox catalysis.

Project description:BackgroundTrifluoromethylated alkene scaffolds are known as useful structural motifs in pharmaceuticals and agrochemicals as well as functional organic materials. But reported synthetic methods usually require multiple synthetic steps and/or exhibit limitation with respect to access to tri- and tetrasubstituted CF3-alkenes. Thus development of new methodologies for facile construction of Calkenyl-CF3 bonds is highly demanded.ResultsThe photoredox reaction of alkenes with 5-(trifluoromethyl)dibenzo[b,d]thiophenium tetrafluoroborate, Umemoto's reagent, as a CF3 source in the presence of [Ru(bpy)3](2+) catalyst (bpy = 2,2'-bipyridine) under visible light irradiation without any additive afforded CF3-substituted alkenes via direct Calkenyl-H trifluoromethylation. 1,1-Di- and trisubstituted alkenes were applicable to this photocatalytic system, providing the corresponding multisubstituted CF3-alkenes. In addition, use of an excess amount of the CF3 source induced double C-H trifluoromethylation to afford geminal bis(trifluoromethyl)alkenes.ConclusionA range of multisubstituted CF3-alkenes are easily accessible by photoredox-catalyzed direct C-H trifluoromethylation of alkenes under mild reaction conditions. In particular, trifluoromethylation of triphenylethene derivatives, from which synthetically valuable tetrasubstituted CF3-alkenes are obtained, have never been reported so far. Remarkably, the present facile and straightforward protocol is extended to double trifluoromethylation of alkenes.

| S-EPMC4077392 | biostudies-literature

Photocatalytic nucleophilic addition of alcohols to styrenes in Markovnikov and anti-Markovnikov orientation.

Project description:The nucleophilic addition of methanol and other alcohols to 1,1-diphenylethylene (1) and styrene (6) into the Markovnikov- and anti-Markovnikov-type products was selectively achieved with 1-(N,N-dimethylamino)pyrene (Py) and 1,7-dicyanoperylene-3,4:9,10-tetracarboxylic acid bisimide (PDI) as photoredox catalysts. The regioselectivity was controlled by the photocatalyst. For the reductive mode towards the Markovnikov-type regioselectivity, Py was applied as photocatalyst and triethylamine as electron shuttle. This approach was also used for intramolecular additions. For the oxidative mode towards the anti-Markovnikov-type regioselectivety, PDI was applied together with Ph-SH as additive. Photocatalytic additions of a variety of alcohols gave the corresponding products in good to excellent yields. The proposed photocatalytic electron transfer mechanism was supported by detection of the PDI radical anion as key intermediate and by comparison of two intramolecular reactions with different electron density. Representative mesoflow reactor experiments allowed to significantly shorten the irradiation times and to use sunlight as "green" light source.

| S-EPMC7877480 | biostudies-literature

Additions of Aldehyde-Derived Radicals and Nucleophilic N-Alkylindoles to Styrenes by Photoredox Catalysis.

Project description:The consecutive addition of acyl radicals and N-alkylindole nucleophiles to styrenes was established, as well as some additional radical-nucleophile combinations. Both aryl and aliphatic aldehydes give reasonable yields. The reaction proceeds best for α-substituted styrenes, effectively creating a quaternary all-carbon center. Some iridium-based photoredox systems are catalytically active; furthermore, a base is needed in this transformation. Radicals are formed by reductive perester cleavage and hydrogen atom transfer.

| S-EPMC7304929 | biostudies-literature

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