Spotlights Cite This: J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
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Spotlights on Recent JACS Publications
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SYNTHESIZING A CORAL’S CHEMICAL DEFENSES Marine corals have a rich chemical arsenal. Now Alois Fürstner and a co-worker have replicated a chemical defense of the Okinawan soft coral of the Sinularia genus and confirmed the utility of certain emerging tools for synthesis (DOI: 10.1021/ jacs.8b12185). The chemical they targeted, sinulariadiolide, is unusual for its tricyclic, nine-membered lactone structure. Lactone-type terpenoids have been shown to have anti-cancer properties in humans, and other coral metabolites have antimicrobial and anti-inflammatory effects. The researchers use transannular stereocontrol, a method that is known for its power to guide chemical reactions but difficult to put into practice, to modify the precursor material. The first attempt failed to trigger sufficient ring contraction in an experimental ring, despite purification and several steps of treatment. The team switched to a precursor substrate with an −OR group and succeeded in establishing a cascade of five replicable, scalable synthetic steps, yielding 86% of the desired material. Spectroscopic analysis of the synthetic sample matched published results for natural sinulariadiolide. The high yield and good match help establish the maturity of transannular stereocontrol methods for similar synthetic work. Lucas Laursen
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HELPING EPOXIDES ALONG WITHOUT NEGATIVE INTERACTIONS Epoxides are strained, three-membered-ring ethers and thus very susceptible to reaction with a wide variety of reagents to create new functional groups. Important in both biology and chemistry, epoxide-opening reactions range from self-programmed cell death in the human body to the production of ether oligomers and polymers in the petrochemical industry. Though the ringopening polymerization of epoxides has been known since the mid-19th century, chemists are only now figuring out how to stabilize and control it. Historically, chemists have been able to stabilize the desired transition states on π-acidic aromatic surfaces. However, usually a Brønsted base is also needed to induce a negative charge to initiate the reactions, which can add complexity and a layer difficulty. In a new paper, Matile and co-workers show that epoxideopening ether cyclization can occur without this additional initiator (DOI: 10.1021/jacs.8b11788). In addition, they find that system can autocatalyze, or continue using the product as a catalyst. Probing this autocatalysis computationally, the group discovers that the transition states form a hydrogen-bonded non-covalent macrocycle. These data could help chemists streamline epoxide-opening reactions to form desired products more quickly, enabling efficient access to targets. Leigh Krietsch Boerner, Ph.D.
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ROOM-TEMPERATURE ORGANIC PHOSPHORESCENCE ILLUMINATED BY MOLECULAR DESCRIPTORS
ALDEHYDE + ALKENE YIELDS ENANTIOSELECTIVE LINEAR PRODUCTS Chemists Jing Li, Alexander Preinfalk, and Nuno Maulide describe a new strategy for the reductive coupling of aldehydes and alkenes to synthesize enantioselective linear products (DOI: 10.1021/jacs.8b12242). Aldehydes and alkenes are readily available feedstocks and thus serve as cheap and widely accessible starting materials. Synthesis of linear products is important, as they are key components in many bioactive compounds that otherwise rely on complicated multi-step syntheses. The ability to generate such enantioselective products is especially appealing for synthetic organic chemists. Enantioselective methods employing classical carbonyl addition reactions have so far been limited to synthesizing branched products, and they typically require activated olefins. Furthermore, using olefins as nucleophiles in synthesis is challenging due to their inherent reactivity and selectivity limitations. Proceeding by an iron-catalyzed “catch-and-release” process that uses an easily accessible chiral functional group as a tether, the strategy presented in this study overcomes these limitations to synthesize products with near-perfect stereoselectivity. This emerging technology holds promise to reinvent carbonyl addition chemistry. Dalia Yablon, Ph.D.
Pure organic materials that undergo room-temperature phosphorescence (RTP) with a long afterglow are highly sought after for a wide array of advanced optoelectronic applications. Most existing phosphors are comprised of inorganic or organometallic materials, making organic phosphors attractive due to their reduced cost and expanded versatility. Despite this, pure organic phosphors are rare, and those that exist have not been able to achieve both high quantum efficiencies and long RTP lifetimes. Now, Qian Peng, Zhigang Shuai, and co-workers have overcome this challenge by identifying molecular descriptors that characterize the phosphorescence efficiencies and lifetimes of pure organic materials (DOI: 10.1021/ jacs.8b11224). Phosphorescence takes place when molecules transition between different orbital states, releasing energy in the form of light. The team built mathematical representations of the (n,π*) and (π,π*) transitions in the lowest-lying singlet and triplet excited states for a particular organic RTP. The researchers validate these representations by performing extensive quantum chemistry calculations for several aromatic carbonyl compounds. The application of these models in the design of organic RTP materials could potentially provide access to new molecules with high efficiencies and long lifetimes. Elizabeth Meucci © XXXX American Chemical Society
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DOI: 10.1021/jacs.9b00435 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
