Photoinduced set generation of α-amineradicals : A practical method for the synthesis of pyrrolidines and piperidines

Pandey, Ganesh; Kumaraswamy, Gullapalli; Bhalerao, U. T.

doi:10.1016/s0040-4039(01)93854-7

Cited by 77 publications

(28 citation statements)

References 19 publications

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“…49 The key intermediate in this reaction is an α-amino radical, a nucleophilic radical that is readily available via photosensitized oxidation of amines, α-amino acids, and α-silylamines. 50,51,52 Prior to our investigations, however, control over the stereochemistry of α-amino radical reactions had remained challenging; the only prior example of an enantioselective photocatalytic reaction involving α-amino radical intermediates was an intramolecular conjugate addition reported by Bach using a chiral hydrogen-bonding photosensitizer. 53 …”

Section: Generality Of the Tandem Photoredox And Chiral Lewis Acid Camentioning

confidence: 99%

Photochemical Stereocontrol Using Tandem Photoredox–Chiral Lewis Acid Catalysis

2016

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Conspectus The physical, biological, and materials properties of organic compounds are determined by their three-dimensional molecular shape. The development of methods to dictate the stereochemistry of organic reactions has consequently emerged as one of the central themes of contemporary synthetic chemistry. Over the past several decades, chiral catalysts have been developed to control the enantioselectivity of almost every class of synthetically useful transformation. Photochemical reactions, however, are a conspicuous exception. Relatively few examples of highly enantioselective catalytic photoreactions have been reported to date, despite almost a century of research in this field. The development of robust strategies for photochemical enantiocontrol has thus proven to be a long-standing and surprisingly difficult challenge. For the past decade, our laboratory has been studying the application of transition metal photocatalysts to a variety of problems in synthetic organic chemistry. These efforts have recently culminated in the discovery of an effective system in which the activity of a visible light absorbing transition metal photoredox catalyst is combined with a second stereocontrolling chiral Lewis acid catalyst. This dual catalyst strategy has been applied to a diverse range of photochemical reactions; these have included highly enantioselective photocatalytic [2+2] cycloadditions, [3+2] cycloadditions, and radical conjugate addition reactions. This Account describes the development of the tandem Lewis acid photoredox catalysis strategy utilized in our laboratory. It provides an analysis of the factors that we believe to be particularly important to the success of this seemingly robust approach to photocatalytic stereocontrol. (1) The photocatalysts utilized in our systems are activated by wavelengths of visible light where the organic substrates are transparent, which minimizes the possibility of competitive racemic background photoreactions. (2) The high degree of tolerance that Ru(bpy)3 2+ and similar octahedral metal polypyridine complexes exhibit towards Lewis acids affords great flexibility in tuning the structure of the stereocontrolling chiral catalyst without perturbing the photoredox properties of the photocatalyst. (3) Synthetic chemists have amassed a substantial understanding of the features that are common in highly successful chiral Lewis acid catalyzed reactions, and these deep, well-validated insights are readily applied to the reactions of a variety of photogenerated intermediates. We hope that the recent success of this and similar dual catalytic systems will provide a useful foundation for the further development of powerful, stereocontrolled photochemical reactions.

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Section: Generality Of the Tandem Photoredox And Chiral Lewis Acid Camentioning

confidence: 99%

Photochemical Stereocontrol Using Tandem Photoredox–Chiral Lewis Acid Catalysis

2016

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“…13 This same fragmentation phenomena had been identified some time ago by Yoon, Mariano, and Pandey in their pioneering photochemical studies using UV irradiation. 14 Because the dual catalytic system is “blind” to the origins of the radical, we surmised that α-silylamines could be integrated into the dual catalytic system (Figure 3). 15 If successful, a dissonant mode of photochemical aminomethylation of aryl halides would be realized and complement existing Ni/photoredox strategies, which are limited to protected amines or aniline-based derivatives.…”

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Aminomethylation of Aryl Halides Using α-Silylamines Enabled by Ni/Photoredox Dual Catalysis

et al. 2017

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A protocol for the aminomethylation of aryl halides using α-silylamines via Ni/photoredox dual catalysis is described. The low oxidation potential of these silylated species enables facile single electron transfer (SET) oxidation of the amine followed by rapid desilylation. The resulting α-amino radicals can be directly funneled into a nickel-mediated cross-coupling cycle with aryl halides. The process accomplishes aminomethylation under remarkably mild conditions and tolerates numerous aryl- and heteroaryl halides with an array of functional groups.

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“…Selective desilylation of compounds 74 by photolysing and DCN yielded pyrrolidines 75 via unstabilized α-amino radical[100] (Scheme 32).…”

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confidence: 99%