Visible light mediated reductions of ethers, amines and sulfides

Monos, Timothy M.; Magallanes, Gabriel; Sebren, Leanne J.; Stephenson, Corey R. J.

doi:10.1016/j.jphotochem.2016.05.014

Cited by 17 publications

(18 citation statements)

References 26 publications

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“…58 Significantly, flow technologies proved beneficial for this system as well, affording significant improvements in terms of reaction time and photocatalyst loading (0.03 mol % 3 , 33 min residence time). The ability to reduce catalyst loading upon transitioning from batch to flow is a common advantage of flow processing, owing this improvement to the more efficient irradiation.…”

Section: Applications In Biofeedstock Processingmentioning

confidence: 99%

Free Radical Chemistry Enabled by Visible Light-Induced Electron Transfer

2016

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ConspectusHarnessing visible light as the driving force for chemical transformations generally offers a more environmentally friendly alternative compared with classical synthetic methodology. The transition metal-based photocatalysts commonly employed in photoredox catalysis absorb efficiently in the visible spectrum, unlike most organic substrates, allowing for orthogonal excitation. The subsequent excited states are both more reducing and more oxidizing than the ground state catalyst and are competitive with some of the more powerful single-electron oxidants or reductants available to organic chemists yet are simply accessed via irradiation. The benefits of this strategy have proven particularly useful in radical chemistry, a field that traditionally employs rather toxic and hazardous reagents to generate the desired intermediates.In this Account, we discuss our efforts to leverage visible light photoredox catalysis in radical-based bond-forming and bond-cleaving events for which few, if any, environmentally benign alternatives exist. Mechanistic investigations have driven our contributions in this field, for both facilitating desired transformations and offering new, unexpected opportunities. In fact, our total synthesis of (+)-gliocladin C was only possible upon elucidating the propensity for various trialkylamine additives to elicit a dual behavior as both a reductive quencher and a H-atom donor. Importantly, while natural product synthesis was central to our initial motivations to explore these photochemical processes, we have since demonstrated applicability within other subfields of chemistry, and our evaluation of flow technologies demonstrates the potential to translate these results from the bench to pilot scale.Our forays into photoredox catalysis began with fundamental methodology, providing a tin-free reductive dehalogenation that exchanged the gamut of hazardous reagents previously employed for such a transformation for visible light-mediated, ambient temperature conditions. Evolving from this work, a new avenue toward atom transfer radical addition (ATRA) chemistry was developed, enabling dual functionalization of both double and triple bonds. Importantly, we have also expanded our portfolio to target clinically relevant scaffolds. Photoredox catalysis proved effective in generating high value fluorinated alkyl radicals through the use of abundantly available starting materials, providing access to libraries of trifluoromethylated (hetero)arenes as well as intriguing gem-difluoro benzyl motifs via a novel photochemical radical Smiles rearrangement. Finally, we discuss a photochemical strategy toward sustainable lignin processing through selective C–O bond cleavage methodology. The collection of these efforts is meant to highlight the potential for visible light-mediated radical chemistry to impact a variety of industrial sectors.

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Section: Applications In Biofeedstock Processingmentioning

confidence: 99%

Free Radical Chemistry Enabled by Visible Light-Induced Electron Transfer

2016

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“…Using synergistic photoredox catalysis with amino organocatalysis MacMillan and co-workers could already demonstrate that α-alkylation of aldehydes can be achieved with common α-bromo acetophenone 12 and, very recently, as well as with significantly less reactive α-acetoxy derivatives as non-traditional radical precursors. 13 , 14 We hence questioned, if such α-acetoxy derived radicals as “alkylation reagent” could provide the required selectivity for a photocatalytic sp 3 –sp 2 C–C cross-coupling with styrenes followed by an oxidation to give the respective Markovnikov-type functionalized products ( Scheme 1 ). This challenging photocatalytic/radical polar crossover reaction would offer unprecedented access to 1,4-functionalized synthons, such as γ-hydroxyketones, being versatile building blocks for the synthesis of a variety of bioactive compounds.…”

Section: Introductionmentioning

confidence: 99%

A synergistic LUMO lowering strategy using Lewis acid catalysis in water to enable photoredox catalytic, functionalizing C–C cross-coupling of styrenes

2018

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“…Recently, Stephenson et al . disclosed an effective approach leveraging photoredox catalysis for the chemoselective reduction of carbon‐heteroatom bonds.…”

Section: Achiral Transformationsmentioning

confidence: 99%

Catalytic Photoreduction Induced by Visible Light

Qiao

2018

ChemPhotoChem

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In 1978, Kellogg et al. described photoreduction of sulfonium ions to the corresponding thioethers and alkanes with tertiary amines as the terminal reductant [Tetrahedron Lett., 1978, 19, 1255. Since then, visible-light-driven photocatalysis, which enables the substrates to undergo an open-shell single-electron transfer to realize important transformations, has attracted significant research interest. Among the many methods inspired by this early report, photoreduction as an extension of Kellogg's work has received particular attention given its ability to provide an expedient and sustainable approach to access valuable compounds from readily accessible feedstocks. Furthermore, the development of distinct reductive procedures presented important foundations to develop other synthetic methodologies for the construction of natural and bioactive non-natural molecules. In this Review, we will discuss advances in this significant research area. The examples are categorized by achiral and chiral reaction patterns with different kinds of starting substrates.

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Visible light mediated reductions of ethers, amines and sulfides

Cited by 17 publications

References 26 publications

Free Radical Chemistry Enabled by Visible Light-Induced Electron Transfer

Free Radical Chemistry Enabled by Visible Light-Induced Electron Transfer

A synergistic LUMO lowering strategy using Lewis acid catalysis in water to enable photoredox catalytic, functionalizing C–C cross-coupling of styrenes

Catalytic Photoreduction Induced by Visible Light

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