Although much effort has been spent on the enantioselective synthesis of tertiary alkyl fluorides, the synthesis of compounds containing such a stereogenic center within an array of stereocenters, particularly two vicinal ones, remains a synthetic challenge, and no method to control the configuration of each stereogenic center independently has been reported. We describe a strategy to achieve such a stereodivergent synthesis of vicinal stereogenic centers, one containing a fluorine atom, by forming the connecting carbon-carbon bond with a catalyst system comprising an iridium complex that controls the configuration at the electrophilic carbon and a copper catalyst that controls the configuration at the nucleophilic fluorine-containing carbon. These reactions occur with alkyl- and aryl-substituted allylic esters and the unstabilized enolates of azaaryl ketones, esters, and amides in high yield, diastereoselectivity, and enantioselectivity (generally >90% yield, >20:1 dr, 97-99% ee). Access to all four stereoisomers of products demonstrates the precise control of the two configurations independently. This methodology extends to the stereodivergent construction of vicinal quaternary and tertiary stereocenters in similarly high yield and selectivity. DFT calculations uncover the origin of stereoselectivity of copper enolate in allylic substitution.
A discrete, dicopper μ-alkynyl complex, [Cu<sub>2</sub>(μ-η<sup>1</sup>:η<sup>1</sup>-C≡C(C<sub>6</sub>H<sub>4</sub>)CH<sub>3</sub>)DPFN]NTf<sub>2</sub> (DPFN = 2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine; NTf<sub>2</sub><sup>-</sup> = N(SO<sub>2</sub>CF<sub>3</sub>)<sub>2</sub><sup>-</sup>), reacts with p-tolylazide to yield a dicopper complex with a symmetrically bridging 1,2,3-triazolide, [Cu<sub>2</sub>(μ-η<sup>1</sup>:η<sup>1</sup>-(1,4-bis(4-tolyl)-1,2,3-triazolide))DPFN]NTf<sub>2</sub>. This transformation exhibits bimolecular reaction kinetics and represents a key step in a proposed, bimetallic mechanism for copper-catalyzed azide-alkyne cycloaddition (CuAAC). The μ-alkynyl and μ-triazolide complexes undergo reversible redox events (by cyclic voltammetry), suggesting that a cycloaddition pathway involving mixed-valence dicopper species might also be possible. Synthesis and characterization of the mixed-valence μ-alkynyl dicopper complex, [Cu<sub>2</sub>(μ-η<sup>1</sup>:η<sup>1</sup>-C≡C(C<sub>6</sub>H<sub>4</sub>)CH<sub>3</sub>)DPFN](NTf<sub>2</sub>)<sub>2</sub>, revealed an electronic structure with an unexpected partially delocalized spin, as evidenced by electron paramagnetic resonance spectroscopy. Studies of the mixed-valence μ-alkynyl complex's reactivity suggest that a mixed-valence pathway is less likely than one involving intermediates with only copper(I).
Hydrogen gas is thought to be the ideal fuel for a world in which air pollution has been alleviated, global warming has been arrested, and the environment has been protected in an economically sustainable manner. Hydrogen and electricity could team to provide attractive options in transportation and power generation. Interconversion between these two forms of energy suggests on-site utilization of hydrogen to generate electricity, with the electrical power grid serving in energy transportation, distribution utilization, and hydrogen regeneration as needed. A challenging problem in establishing H2 as a source of energy for the future is the renewable and environmentally friendly generation of large quantities of H2 gas. Thus, processes that are presently conceptual in nature, or at a developmental stage in the laboratory, need to be encouraged, tested for feasibility, and otherwise applied toward commercialization.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
This paper focuses on the migration patterns of residents of the community of San Mateo, San Pedro, Belize.Recent research conducted in the community of San Mateo by Florida State University faculty and students revealed numerous vacant lots along the coast and in areas where water has risen and not been displaced.In total, the vacant lots accounted for nearly a quarter of the community.Drawing from these findings, this paper argues that these vacant lots are due to environmental changes in the community, most likely attributed to climate change.This paper will examine environmental migration in San Mateo as well as availability of resources such as electricity and water.The ultimate goal of this research is to assess how the resettlement of environmental migrants is impacted by the availability of resources.The paper will subsequently illustrate that Central America is especially prone to the effects of climate change, and that this directly impacts the most vulnerable, coastal communities.
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