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1. Scalable Birch reduction with lithium and ethylenediamine in tetrahydrofuran

   https://doi.org/10.1126/science.abk3099  

   Burrows, James; Kamo, Shogo; Koide, Kazunori (November 2021, Science)

   The Birch reduction dearomatizes arenes into 1,4-cyclohexadienes. Despite substantial efforts devoted to avoiding ammonia and cryogenic conditions, the traditional, cumbersome, and dangerous procedure remains the standard. The Benkeser reduction with lithium in ethylenediamine converts arenes to a mixture of cyclohexenes and cyclohexanes; this is operationally easier than the Birch reduction but does not afford 1,4-cyclohexadienes. Here, we report a Birch reduction promoted by lithium and ethylenediamine (or analogs) in tetrahydrofuran at ambient temperature. Our method is easy to set up, inexpensive, scalable, rapid, accessible to any chemical laboratory, and capable of reducing both electron-rich and electron-deficient substrates. Our protocol is also compatible with organocuprate chemistry for further functionalization. 

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2. Mechanistic and Synthetic Studies of Biaryl Birch Reductions

   https://doi.org/10.1055/s-0042-1751387  

   Koide, Kazunori (February 2023, Synthesis)

   Abstract The Birch reduction of biaryls generally converts one of the two arenes into a cyclohexa-1,4-diene. Biaryls are more reactive than monocyclic arenes under the Birch conditions. Unlike the reduction of monocyclic arenes, biaryl reduction proceeds through two consecutive electron transfer steps before the protonation of the dianion intermediate. The biaryl reductions and subsequent alkylations in one pot rapidly increase the molecular complexity and thus have been used in the synthesis of natural products and drug-like molecules. 1 Introduction 2 The Physical Organic Chemistry of the Birch Reduction of Biaryls 3 Biaryls as the Mediators of Electron Transfer 4 Methods for the Dissolving-Metal Reduction of Biaryls 5 Intercepting the Biaryl Reduction Intermediates with Electrophiles 6 Synthetic Applications of the Dissolving-Metal-Mediated Reductions of Biaryls 7 Outlook 

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3. On perfectness in Gaussian graphical models

   Amini, Arash A.; Aragam, Bryon; Zhou, Qing (March 2022, Proceedings of The 25th International Conference on Artificial Intelligence and Statistics)

   Camps-Valls, G.; Ruiz, F. J.; Valera, I. (Ed.)

   Knowing when a graphical model perfectly encodes the conditional independence structure of a distribution is essential in applications, and this is particularly important when performing inference from data. When the model is perfect, there is a one-to-one correspondence between conditional independence statements in the distribution and separation statements in the graph. Previous work has shown that almost all models based on linear directed acyclic graphs as well as Gaussian chain graphs are perfect, the latter of which subsumes Gaussian graphical models (i.e., the undirected Gaussian models) as a special case. In this paper, we directly approach the problem of perfectness for the Gaussian graphical models, and provide a new proof, via a more transparent parametrization, that almost all such models are perfect. Our approach is based on, and substantially extends, a construction of Lněnička and Matúš showing the existence of a perfect Gaussian distribution for any graph. The analysis involves constructing a probability measure on the set of normalized covariance matrices Markov with respect to a graph that may be of independent interest. 

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4. Evaluation of the Catalytic Relevance of the CO‐Bound States of V‐Nitrogenase

   https://doi.org/10.1002/anie.201800189  

   Lee, Chi Chung; Wilcoxen, Jarett; Hiller, Caleb J.; Britt, R. David; Hu, Yilin (March 2018, Angewandte Chemie International Edition)

   Abstract Binding and activation of CO by nitrogenase is a topic of interest because CO is isoelectronic to N₂, the physiological substrate of this enzyme. The catalytic relevance of one‐ and multi‐CO‐bound states (the lo‐CO and hi‐CO states) of V‐nitrogenase to C−C coupling and N₂reduction was examined. Enzymatic and spectroscopic studies demonstrate that the multiple CO moieties in the hi‐CO state cannot be coupled as they are, suggesting that C−C coupling requires further activation and/or reduction of the bound CO entity. Moreover, these studies reveal an interesting correlation between decreased activity of N₂reduction and increased population of the lo‐CO state, pointing to the catalytic relevance of the belt Fe atoms that are bridged by the single CO moiety in the lo‐CO state. Together, these results provide a useful framework for gaining insights into the nitrogenase‐catalyzed reaction via further exploration of the utility of the lo‐CO conformation of V‐nitrogenase. 

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5. A Bioinspired Molybdenum Catalyst for Aqueous Perchlorate Reduction

   https://doi.org/10.1021/jacs.1c00595  

   Ren, Changxu; Yang, Peng; Sun, Jiaonan; Bi, Eric Y.; Gao, Jinyu; Palmer, Jacob; Zhu, Mengqiang; Wu, Yiying; Liu, Jinyong (May 2021, Journal of the American Chemical Society)

   null (Ed.)

   Perchlorate (ClO4–) is a pervasive, harmful, and inert anion on both Earth and Mars. Current technologies for ClO4– reduction entail either harsh conditions or multicomponent enzymatic processes. Herein, we report a heterogeneous (L)Mo–Pd/C catalyst directly prepared from Na2MoO4, a bidentate nitrogen ligand (L), and Pd/C to reduce aqueous ClO4– into Cl– with 1 atm of H2 at room temperature. A suite of instrument characterizations and probing reactions suggest that the MoVI precursor and L at the optimal 1:1 ratio are transformed in situ into oligomeric MoIV active sites at the carbon–water interface. For each Mo site, the initial turnover frequency (TOF0) for oxygen atom transfer from ClOx– substrates reached 165 h–1. The turnover number (TON) reached 3840 after a single batch reduction of 100 mM ClO4–. This study provides a water-compatible, efficient, and robust catalyst to degrade and utilize ClO4– for water purification and space exploration. 

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