Asymmetric copper-catalyzed C-N cross-couplings induced by visible light.
12 Feb 2016-Science (American Association for the Advancement of Science)-Vol. 351, Iss: 6274, pp 681-684
TL;DR: A photoinduced copper-catalyzed method for coupling readily available racemic tertiary alkyl chloride electrophiles with amines to generate fully substituted stereocenters with high enantioselectivity is described.
Abstract: Despite a well-developed and growing body of work in copper catalysis, the potential of copper to serve as a photocatalyst remains underexplored. Here we describe a photoinduced copper-catalyzed method for coupling readily available racemic tertiary alkyl chloride electrophiles with amines to generate fully substituted stereocenters with high enantioselectivity. The reaction proceeds at –40°C under excitation by a blue light-emitting diode and benefits from the use of a single, Earth-abundant transition metal acting as both the photocatalyst and the source of asymmetric induction. An enantioconvergent mechanism transforms the racemic starting material into a single product enantiomer.
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References
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TL;DR: This paper could serve as a general literature citation when one or more of the open-source SH ELX programs (and the Bruker AXS version SHELXTL) are employed in the course of a crystal-structure determination.
Abstract: An account is given of the development of the SHELX system of computer programs from SHELX-76 to the present day. In addition to identifying useful innovations that have come into general use through their implementation in SHELX, a critical analysis is presented of the less-successful features, missed opportunities and desirable improvements for future releases of the software. An attempt is made to understand how a program originally designed for photographic intensity data, punched cards and computers over 10000 times slower than an average modern personal computer has managed to survive for so long. SHELXL is the most widely used program for small-molecule refinement and SHELXS and SHELXD are often employed for structure solution despite the availability of objectively superior programs. SHELXL also finds a niche for the refinement of macromolecules against high-resolution or twinned data; SHELXPRO acts as an interface for macromolecular applications. SHELXC, SHELXD and SHELXE are proving useful for the experimental phasing of macromolecules, especially because they are fast and robust and so are often employed in pipelines for high-throughput phasing. This paper could serve as a general literature citation when one or more of the open-source SHELX programs (and the Bruker AXS version SHELXTL) are employed in the course of a crystal-structure determination.
81,116 citations
TL;DR: OLEX2 seamlessly links all aspects of the structure solution, refinement and publication process and presents them in a single workflow-driven package, with the ultimate goal of producing an application which will be useful to both chemists and crystallographers.
Abstract: New software, OLEX2, has been developed for the determination, visualization and analysis of molecular crystal structures. The software has a portable mouse-driven workflow-oriented and fully comprehensive graphical user interface for structure solution, refinement and report generation, as well as novel tools for structure analysis. OLEX2 seamlessly links all aspects of the structure solution, refinement and publication process and presents them in a single workflow-driven package, with the ultimate goal of producing an application which will be useful to both chemists and crystallographers.
19,990 citations
"Asymmetric copper-catalyzed C-N cro..." refers methods in this paper
...C(34) 24(1) 19(1) 20(1) 4(1) 6(1) 0(1) C(35) 20(1) 21(1) 18(1) -1(1) 4(1) 2(1) C(36) 19(1) 16(1) 19(1) 1(1) 2(1) 2(1) C(37) 20(1) 14(1) 23(1) 0(1) 5(1) -4(1) C(38) 16(1) 22(1) 28(1) -1(1) 3(1) -3(1) C(39) 15(1) 18(1) 21(1) 2(1) 0(1) 2(1) C(40) 17(1) 15(1) 14(1) 1(1) 0(1) 3(1) C(41) 19(1) 18(1) 15(1) 2(1) -1(1) 1(1) C(42) 29(1) 18(1) 16(1) -1(1) -2(1) 2(1) C(43) 28(1) 24(1) 18(1) -1(1) 5(1) 8(1) C(44) 19(1) 24(1) 22(1) 5(1) 6(1) 5(1) C(45) 15(1) 14(1) 17(1) 0(1) 5(1) 1(1)...
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...Using Olex2 (36), the structure was solved with the ShelXS structure solution program using Direct Methods and refined with the ShelXL refinement package (37) using Least Squares minimization....
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...C(34) 8661(2) 9480(1) -1121(1) 21(1) C(35) 8920(2) 8642(1) -1170(1) 20(1) C(36) 8128(2) 8262(1) -662(1) 18(1) C(37) 4753(2) 8311(1) 1183(1) 19(1) C(38) 3647(2) 8507(1) 1554(1) 22(1) C(39) 3953(2) 9229(1) 1881(1) 18(1) C(40) 4916(2) 9534(1) 1578(1) 15(1) C(41) 5388(2) 10201(1) 1791(1) 17(1) C(42) 4848(2) 10565(1) 2311(1) 21(1) C(43) 3880(2) 10270(1) 2610(1) 23(1) C(44) 3434(2) 9596(1) 2399(1) 22(1) C(45) 6518(2) 7213(1) 236(1) 15(1)...
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TL;DR: The conversion of these bench stable, benign catalysts to redox-active species upon irradiation with simple household lightbulbs represents a remarkably chemoselective trigger to induce unique and valuable catalytic processes.
Abstract: A fundamental aim in the field of catalysis is the development of new modes of small molecule activation. One approach toward the catalytic activation of organic molecules that has received much attention recently is visible light photoredox catalysis. In a general sense, this approach relies on the ability of metal complexes and organic dyes to engage in single-electron-transfer (SET) processes with organic substrates upon photoexcitation with visible light.
Many of the most commonly employed visible light photocatalysts are polypyridyl complexes of ruthenium and iridium, and are typified by the complex tris(2,2′-bipyridine) ruthenium(II), or Ru(bpy)32+ (Figure 1). These complexes absorb light in the visible region of the electromagnetic spectrum to give stable, long-lived photoexcited states.1,2 The lifetime of the excited species is sufficiently long (1100 ns for Ru(bpy)32+) that it may engage in bimolecular electron-transfer reactions in competition with deactivation pathways.3 Although these species are poor single-electron oxidants and reductants in the ground state, excitation of an electron affords excited states that are very potent single-electron-transfer reagents. Importantly, the conversion of these bench stable, benign catalysts to redox-active species upon irradiation with simple household lightbulbs represents a remarkably chemoselective trigger to induce unique and valuable catalytic processes.
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Figure 1
Ruthenium polypyridyl complexes: versatile visible light photocatalysts.
6,252 citations
TL;DR: A variety of reaction types have now been shown to be amenable to visible light photocatalysis via photoinduced electron transfer to or from the transition metal chromophore, as well as energy-transfer processes.
Abstract: Background Interest in photochemical synthesis has been motivated in part by the realization that sunlight is effectively an inexhaustible energy source.Chemists have also long recognized distinctive patterns of reactivity that are uniquely accessible via photochemical activation. However, most simple organic molecules absorb only ultraviolet (UV) light and cannot be activated by the visible wavelengths that comprise most of the solar energy that reaches Earth’s surface. Consequently, organic photochemistry has generally required the use of UV light sources. Visible light photocatalysis. ( A ) Transition metal photocatalysts, such as Ru(bpy) 3 2+ , readily absorb visible light to access reactive excited states. ( B ) Photoexcited Ru*(bpy) 3 2+ can act as an electron shuttle, interacting with sacrificial electron donors D (path i) or acceptors A (path ii) to yield either a strongly reducing or oxidizing catalyst toward organic substrates S. Ru*(bpy) 3 2+ can also directly transfer energy to an organic substrate to yield electronically excited species (path iii). bpy, 2,29-bipyridine; MLCT, metal-to-ligand charge transfer. Advances Over the past several years, there has been a resurgence of interest in synthetic photochemistry, based on the recognition that the transition metal chromophores that have been so productively exploited in the design of technologies for solar energy conversion can also convert visible light energy into useful chemical potential for synthetic purposes. Visible light enables productive photoreactions of compounds possessing weak bonds that are sensitive toward UV photodegradation. Furthermore, visible light photoreactions can be conducted by using essentially any source of white light, including sunlight, which obviates the need for specialized UV photoreactors. This feature has expanded the accessibility of photochemical reactions to a broader range of synthetic organic chemists. A variety of reaction types have now been shown to be amenable to visible light photocatalysis via photoinduced electron transfer to or from the transition metal chromophore, as well as energy-transfer processes. The predictable reactivity of the intermediates generated and the tolerance of the reaction conditions to a wide range of functional groups have enabled the application of these reactions to the synthesis of increasingly complex target molecules. Outlook This general strategy for the use of visible light in organic synthesis is already being adopted by a growing community of synthetic chemists. Much of the current research in this emerging area is geared toward the discovery of photochemical solutions for increasingly ambitious synthetic goals. Visible light photocatalysis is also attracting the attention of researchers in chemical biology, materials science, and drug discovery, who recognize that these reactions offer opportunities for innovation in areas beyond traditional organic synthesis. The long-term goals of this emerging area are to continue to improve efficiency and synthetic utility and to realize the long-standing goal of performing chemical synthesis using the sun.
1,859 citations
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