Silylium‐Ion‐Promoted (5+1) Cycloaddition of Aryl‐Substituted Vinylcyclopropanes and Hydrosilanes Involving Aryl Migration

Silylium‐Ion‐Promoted (5+1) Cycloaddition of Aryl‐Substituted Vinylcyclopropanes and Hydrosilanes Involving Aryl Migration

Re‐Arrangement silicissimo ! Vinylcyclopropanes (VCPs) undergo a formal (5+1) cycloaddition when reacted with in situ generated silylium ions. The bond reorganization is connected to an aryl migration to eventually yield a silacyclohexane derivative which is regioisomeric to the expected product. Reaction mechanisms that rationalize the formation of the major and minor products are presented based on a series of control experiments and quantum‐chemical calculations.

Abstract

A transition‐metal‐free (5+1) cycloaddition of aryl‐substituted vinylcyclopropanes (VCPs) and hydrosilanes to afford silacyclohexanes is reported. Catalytic amounts of the trityl cation initiate the reaction by hydride abstraction from the hydrosilane, and further progress of the reaction is maintained by self‐regeneration of the silylium ions. The new reaction involves a [1,2] migration of an aryl group, eventually furnishing 4‐ rather than 3‐aryl‐substituted silacyclohexane derivatives as major products. Various control experiments and quantum‐chemical calculations support a mechanistic picture where a silylium ion intramolecularly stabilized by a cyclopropane ring can either undergo a kinetically favored concerted [1,2] aryl migration/ring expansion or engage in a cyclopropane‐to‐cyclopropane rearrangement.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Tao He, Guoqiang Wang, Vittorio Bonetti, Hendrik F. T. Klare, Martin Oestreich
doi.org/10.1002/anie.202004320

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Complex Polypropionates from a South China Sea Photosynthetic Mollusk: Isolation and Biomimetic Synthesis Highlighting Novel Rearrangements

Complex Polypropionates from a South China Sea Photosynthetic Mollusk: Isolation and Biomimetic Synthesis Highlighting Novel Rearrangements

A series of racemic polypropionates with novel polycyclic skeletons were discovered and structurally elucidated from the South China Sea photosynthetic sacoglossan mollusk Placobranchus ocellatus . An array of new and diversity‐generating rearrangements is proposed to explain the biosynthesis of these unusual compounds. Furthermore, the successful biomimetic semisynthesis of ocellatusone A confirmed the proposed rearrangement through an unprecedented acid induced cascade reaction.

Abstract

Placobranchus ocellatus is well known to produce diverse and complex γ‐pyrone polypropionates. In this study, the chemical investigation of P. ocellatus from the South China Sea led to the discovery and identification of ocellatusones A–D, a series of racemic non‐γ‐pyrone polyketides with novel skeletons, characterized by a bicyclo[3.2.1]octane (1 , 2 ), a bicyclo[3.3.1]nonane (3 ) or a mesitylene‐substituted dimethylfuran‐3(2H )‐one core (4 ). Extensive spectroscopic analysis, quantum chemical computation, chemical synthesis, and/or X‐ray diffraction analysis were used to determine the structure and absolute configuration of the new compounds, including each enantiomer of racemic compounds 1 4 after chiral HPLC resolution. An array of new and diversity‐generating rearrangements is proposed to explain the biosynthesis of these unusual compounds based on careful structural analysis and comparison with six known co‐occurring γ‐pyrones (5 10 ). Furthermore, the successful biomimetic semisynthesis of ocellatusone A (1 ) confirmed the proposed rearrangement through an unprecedented acid induced cascade reaction.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Qihao Wu, Song‐Wei Li, Heng Xu, Hong Wang, Pei Hu, Hao Zhang, Cheng Luo, Kai‐Xian Chen, Bastien Nay, Yue‐Wei Guo, Xu‐Wen Li
doi.org/10.1002/anie.202003643

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Palladium‐Catalyzed Enantioselective Heck Carbonylation with a Monodentate Phosphoramidite Ligand: Asymmetric Synthesis of (+)‐Physostigmine, (+)‐Physovenine, and (+)‐Folicanthine

Palladium‐Catalyzed Enantioselective Heck Carbonylation with a Monodentate Phosphoramidite Ligand: Asymmetric Synthesis of (+)‐Physostigmine, (+)‐Physovenine, and (+)‐Folicanthine

Domino reaction : A new monodentate phosphoramidite ligand, Xida‐Phos, was used in the enantioselective Pd‐catalyzed domino Heck carbonylative reaction for the synthesis of oxindoles having β‐carbonyl‐substituted all‐carbon quaternary centers. The reaction was used in the asymmetric synthesis of bioactive hexahydropyrroloindole (HPI) and its dimeric alkaloids.

Abstract

Reported herein is the development of the first enantioselective monodentate ligand assisted Pd‐catalyzed domino Heck carbonylation reaction with CO. The highly enantioselective domino Heck carbonylation of N‐aryl acrylamides and various nucleophiles, including arylboronic acids, anilines, and alcohols, in the presence of CO was achieved. A novel monodentate phosphoramidite ligand, Xida‐Phos, has been developed for this reaction and it displays excellent reactivity and enantioselectivity. The reaction employs readily available starting materials, tolerates a wide range of functional groups, and provides straightforward access to a diverse array of enantioenriched oxindoles having β‐carbonyl‐substituted all‐carbon quaternary stereocenters, thus providing a facile and complementary method for the asymmetric synthesis of bioactive hexahydropyrroloindole and its dimeric alkaloids.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Ming Chen, Xucai Wang, Pengfei Yang, Xun Kou, Zhi‐Hui Ren, Zheng‐Hui Guan
doi.org/10.1002/anie.202003288

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Sterically Controlled C−H Olefination of Heteroarenes

Sterically Controlled C−H Olefination of Heteroarenes

Getting choosy : In a new sterically controlled C−H olefination, heteroarenes serve as the limiting reagent. The method enables the highly C5‐selective olefination of a wide range of heteroarenes and is shown to be useful in the context of late‐stage functionalization.

Abstract

The regioselective functionalization of heteroarenes is a highly attractive synthetic target due to the prevalence of multiply substituted heteroarenes in nature and bioactive compounds. Some substitution patterns remain challenging: While highly efficient methods for the C2‐selective olefination of 3‐substituted five‐membered heteroarenes have been reported, analogous methods to access the 5‐olefinated products have remained limited by poor regioselectivities and/or the requirement to use an excess of the valuable heteroarene starting material. Herein we report a sterically controlled C−H olefination using heteroarenes as the limiting reagent. The method enables the highly C5‐selective olefination of a wide range of heteroarenes and is shown to be useful in the context of late‐stage functionalization.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Hao Chen, Mirxan Farizyan, Francesca Ghiringhelli, Manuel Gemmeren
doi.org/10.1002/anie.202004521

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Selective Hydrogenation and Hydrodeoxygenation of Aromatic Ketones to Cyclohexane Derivatives Using a Rh@SILP Catalyst

Selective Hydrogenation and Hydrodeoxygenation of Aromatic Ketones to Cyclohexane Derivatives Using a Rh@SILP Catalyst

Some like it hot : Rhodium nanoparticles immobilized on an acid‐free triphenylphosphonium‐based supported ionic liquid phase (Rh@SILP(Ph3‐P‐NTf2)) enabled ready access to high‐value cyclohexane derivatives from aromatic ketones. The product distribution could be switched with high selectivity between the completely hydrogenated (alcohol) and hydrodeoxygenated (alkane) products by changing the reaction temperature (see scheme).

Abstract

Rhodium nanoparticles immobilized on an acid‐free triphenylphosphonium‐based supported ionic liquid phase (Rh@SILP(Ph3‐P‐NTf2)) enabled the selective hydrogenation and hydrodeoxygenation of aromatic ketones. The flexible molecular approach used to assemble the individual catalyst components (SiO2, ionic liquid, nanoparticles) led to outstanding catalytic properties. In particular, intimate contact between the nanoparticles and the phosphonium ionic liquid is required for the deoxygenation reactivity. The Rh@SILP(Ph3‐P‐NTf2) catalyst was active for the hydrodeoxygenation of benzylic ketones under mild conditions, and the product distribution for non‐benzylic ketones was controlled with high selectivity between the hydrogenated (alcohol) and hydrodeoxygenated (alkane) products by adjusting the reaction temperature. The versatile Rh@SILP(Ph3‐P‐NTf2) catalyst opens the way to the production of a wide range of high‐value cyclohexane derivatives by the hydrogenation and/or hydrodeoxygenation of Friedel–Crafts acylation products and lignin‐derived aromatic ketones.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Gilles Moos, Meike Emondts, Alexis Bordet, Walter Leitner
doi.org/10.1002/anie.201916385

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Photon Equivalents as a Parameter for Scaling Photoredox Reactions in Flow: Translation of Photocatalytic C−N Cross‐Coupling from Lab Scale to Multikilogram Scale

Photon Equivalents as a Parameter for Scaling Photoredox Reactions in Flow: Translation of Photocatalytic C−N Cross‐Coupling from Lab Scale to Multikilogram Scale

Size matters : A predictive scaling parameter for photochemical reactions, absorbed photon equivalents, was established by a study of how a photoredox cross‐coupling reaction performed across multiple reactor sizes and types. The parameter could be employed in the successful scale‐up of this model reaction from the milligram scale in batch to the multi‐kilogram scale in flow.

Abstract

With the development of new photocatalytic methods over recent decades, the translation of these chemical reactions to industrial‐production scales using continuous‐flow reactors has become a topic of increasing interest. In this context, we describe our studies toward elucidating an empirically derived parameter for scaling photocatalytic reactions in flow. By evaluating the performance of a photocatalytic C−N cross‐coupling reaction across multiple reactor sizes and geometries, it was demonstrated that expressing product yield as a function of the absorbed photon equivalents provides a predictive, empirical scaling parameter. Through the use of this scaling factor and characterization of the photonic flux within each reactor, the cross‐coupling was scaled successfully from the milligram scale in batch to a multi‐kilogram reaction in flow.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Emily B. Corcoran, Jonathan P. McMullen, François Lévesque, Michael K. Wismer, John R. Naber
doi.org/10.1002/anie.201915412

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Strain Influences the Hydrogen Evolution Activity and Absorption Capacity of Palladium

Strain Influences the Hydrogen Evolution Activity and Absorption Capacity of Palladium

Tensile strain increases the hydrogen evolution reaction rate and decreases hydrogen absorption at a palladium surface. A custom electrochemical cell is reported that applies tensile strain to a flexible working electrode, thus enabling the effect of tensile strain on hydrogen absorption and HER activity for a thin film palladium electrocatalyst to be resolved.

Abstract

Strain engineering can increase the activity and selectivity of an electrocatalyst. Tensile strain is known to improve the electrocatalytic activity of palladium electrodes for reduction of carbon dioxide or dioxygen, but determining how strain affects the hydrogen evolution reaction (HER) is complicated by the fact that palladium absorbs hydrogen concurrently with HER. We report here a custom electrochemical cell, which applies tensile strain to a flexible working electrode, that enabled us to resolve how tensile strain affects hydrogen absorption and HER activity for a thin film palladium electrocatalyst. When the electrodes were subjected to mechanically‐applied tensile strain, the amount of hydrogen that absorbed into the palladium decreased, and HER electrocatalytic activity increased. This study showcases how strain can be used to modulate the hydrogen absorption capacity and HER activity of palladium.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Ryan P. Jansonius, Phil A. Schauer, David J. Dvorak, Benjamin P. MacLeod, David K. Fork, Curtis P. Berlinguette
doi.org/10.1002/anie.202005248

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Protection Strategies Enable Selective Conversion of Biomass

Protection Strategies Enable Selective Conversion of Biomass

Catalytic conversion of biomass to fuels and chemicals is fraught with low selectivity. This Minireview provides an overview of the physical and chemical protection strategies used to improve selectivity in biomass conversion and describes the potential of using protection chemistry to manipulate catalytic pathways.

Abstract

Selective and economic conversion of lignocellulosic biomass components to bio‐based fuels and chemicals is the major goal of biorefineries, but low yields and selectivity for fuel precursors such as sugars, furanics, and lignin‐derived monomers pose significant disadvantages in process economics. In this Minireview we summarize the existing protection strategies used in biomass chemocatalytic conversion processes and focus the discussions on the mechanisms, challenges, and opportunities of each strategy. We introduce a concept of using analogous methods to manipulate biomass catalytic conversion pathways during the upgrading of carbohydrates to fuels and chemicals. This Minireview may provide new insights into the development of selective biorefining processes from a different perspective, expanding the options for selective conversion of biomass to fuels and chemicals.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Xiaolin Luo, Yanding Li, Navneet Kumar Gupta, Bert Sels, John Ralph, Li Shuai
doi.org/10.1002/anie.201914703

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Photo‐promoted Skeletal Rearrangement of Phosphine–Borane Frustrated Lewis Pairs Involving Cleavage of Unstrained C−C σ‐Bonds

Photo‐promoted Skeletal Rearrangement of Phosphine–Borane Frustrated Lewis Pairs Involving Cleavage of Unstrained C−C σ‐Bonds

Unstrained melody : A photo‐promoted skeletal rearrangement reaction of phosphine–borane frustrated Lewis pairs, o‐(borylaryl)phosphines, involving cleavage of an unstrained sp2C–sp3C σ‐bond is reported. The reaction realizes an efficient synthesis of cyclic phosphonium borate compounds. The reaction mechanism via a boranorcaradiene intermediate is proposed based on calculations.

Abstract

An unprecedented photo‐promoted skeletal rearrangement reaction of phosphine–borane frustrated Lewis pairs, o‐(borylaryl)phosphines, involving cleavage of an unstrained sp2C–sp3C σ‐bond is reported. The reaction realizes an efficient synthesis of cyclic phosphonium borate compounds. The reaction mechanism via a boranorcaradiene intermediate is proposed based on theoretical calculations. This work sheds light on the new photoreactivity of phosphine–borane FLPs.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Tatsuyoshi Ito, Nobuharu Iwasawa, Jun Takaya
doi.org/10.1002/anie.202004444

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A “Push–Pull” Stabilized Phosphinidene Supported by a Phosphine‐Functionalized β‐Diketiminato Ligand

A “Push–Pull” Stabilized Phosphinidene Supported by a Phosphine‐Functionalized β‐Diketiminato Ligand

The synthesis and reactivity of a family of germanium(II) and tin(II) complexes supported by a bis(diphenyl)phosphine functionalized β‐diketiminato ligand is reported, including an intramolecularly stabilized “push–pull” phosphinidene.

Abstract

The use of a bis(diphenyl)phosphine functionalized β‐diketiminato ligand, [HC{(CH3)C}2{(ortho‐[P(C6H5)2]2C6H4)N}2] (PNac), as a support for germanium(II) and tin(II) chloride and phosphaketene compounds, is described. The conformational flexibility and hemilability of this unique ligand provide a versatile coordination environment that can accommodate the electronic needs of the ligated elements. For example, chloride abstraction from [(PNac)ECl] (E=Ge, Sn) affords the cationic germyliumylidene and stannyliumylidene species [(PNac)E]+ in which the pendant phosphine arms associate more strongly with the Lewis acidic main group element centers, providing further electronic stabilization. In a similar fashion, chemical decarbonylation of the germanium phosphaketene [(PNac)Ge(PCO)] with tris(pentafluorophenyl)borane affords a “push–pull” stabilized phosphinidene in which one of the phosphine groups of the ligand backbone associates with the low valent phosphinidene center.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Sebastian Bestgen, Meera Mehta, Timothy C. Johnstone, Peter W. Roesky, Jose M. Goicoechea
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202001762

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Identifying the Target of an Antiparasitic Compound in Toxoplasma Using Thermal Proteome Profiling

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ACS Chemical Biology

ACS Chemical Biology: Latest Articles (ACS Publications)
Authors: Alice L. Herneisen†‡, Saima M. Sidik‡, Benedikt M. Markus‡§, David H. Drewry??, William J. Zuercher?, and Sebastian Lourido*†‡
feedproxy.google.com/~r/acs/acbcct/~3/WJrXkN42d-c/acschembio.0c00369

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Next-Generation TLC: A Quantitative Platform for Parallel Spotting and Imaging

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The Journal of Organic Chemistry

The Journal of Organic Chemistry: Latest Articles (ACS Publications)
Authors: Alexander A. Boulgakov†#, Sarah R. Moor‡#, Hyun Hwa Jo‡#, Pedro Metola‡, Leo A. Joyce§?, Edward M. Marcotte†, Christopher J. Welch*§?, and Eric V. Anslyn*†
feedproxy.google.com/~r/acs/joceah/~3/oGilf9047VI/acs.joc.0c00349

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Discovery of Novel Antibiotics as Covalent Inhibitors of Fatty Acid Synthesis

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ACS Chemical Biology

ACS Chemical Biology: Latest Articles (ACS Publications)
Authors: Jia Wang†, Xiaoping Ye†, Xiaohan Yang†, Youyan Cai†, Shengjun Wang†, Jieyu Tang†, Meena Sachdeva§?, Yu Qian†, Wenhao Hu†, Jennifer A. Leeds§?, and Yanqiu Yuan*†‡
feedproxy.google.com/~r/acs/acbcct/~3/QPv0V_l8I5g/acschembio.9b00982

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Discovery of Dihydropyrrolo[1,2-a]pyrazin-3(4H)-one-Based Second-Generation GluN2C- and GluN2D-Selective Positive Allosteric Modulators (PAMs) of the N-Methyl-d-Aspartate (NMDA) Receptor

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Journal of Medicinal Chemistry

Journal of Medicinal Chemistry: Latest Articles (ACS Publications)
Authors: Matthew P. Epplin†, Ayush Mohan†, Lynnea D. Harris†, Zongjian Zhu‡, Katie L. Strong†, John Bacsa†, Phuong Le‡, David S. Menaldino†, Stephen F. Traynelis*‡, and Dennis C. Liotta*†
feedproxy.google.com/~r/acs/jmcmar/~3/14GwdcB2vm0/acs.jmedchem.9b01733

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Structures and Biosynthetic Pathway of Pulvomycins B–D: 22-Membered Macrolides from an Estuarine Streptomyces sp.

Organic Letters: Latest Articles (ACS Publications)
Authors: Kyuho Moon†‡?, Jinsheng Cui†?, Eunji Kim†, Evan Setiawan Riandi†, So Hyun Park†, Woong Sub Byun†, Youngju Kal§, Jun Young Park§, Sunghoon Hwang†, Daniel Shin†, Jeongyoon Sun?, Ki-Bong Oh?, Sangwon Cha§, Jongheon Shin†, Sang Kook Lee†, Yeo Joon Yoon†, and Dong-Chan Oh*†
feedproxy.google.com/~r/acs/orlef7/~3/O-XfEprmwiM/acs.orglett.0c01249

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Discovery of A-1331852, a First-in-Class, Potent, and Orally-Bioavailable BCL-XL Inhibitor

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ACS Medicinal Chemistry Letters

ACS Medicinal Chemistry Letters: Latest Articles (ACS Publications)
Authors: Le Wang†, George A. Doherty†, Andrew S. Judd*†, Zhi-Fu Tao†, T. Matthew Hansen†, Robin R. Frey†, Xiaohong Song†, Milan Bruncko†, Aaron R. Kunzer†, Xilu Wang†, Michael D. Wendt†, John A. Flygare§#, Nathaniel D. Catron†, Russell A. Judge†, Chang H. Park†, Shashank Shekhar†, Darren C. Phillips†, Paul Nimmer†, Morey L. Smith†, Stephen K. Tahir†, Yu Xiao†, John Xue†, Haichao Zhang†, Phuong N. Le†, Michael J. Mitten†, Erwin R. Boghaert†, Wenqing Gao†, Peter Kovar†, Edna F. Choo§, Dolores Diaz§?, Wayne J. Fairbrother§, Steven W. Elmore†, Deepak Sampath§?, Joel D. Leverson†, and Andrew James Souers†
feedproxy.google.com/~r/acs/amclct/~3/c0aozCJa-Fw/acsmedchemlett.9b00568

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