1,145 results match your criteria ring-closure reaction

Unraveling the bonding nature along the photochemically activated Paterno-Büchi reaction mechanism.

Chemphyschem 2021 Sep 21. Epub 2021 Sep 21.

Universidad Andrés Bello: Universidad Andres Bello, Facultad de Ciencias Exactas, Avenida, República 275, 8370146, Santiago de Chile, CHILE.

The photochemically activated Paterno-Büchi reaction mechanism following the singlet excited-state reaction path was analyzed based on a bonding evolution framework. The electronic rearrangements, which describe the mechanism of oxetane formation via carbon-oxygen attack (C-O), comprise the electronic activation of formaldehyde accumulating of pairing density on the O once the reaction system is approaching the conical intersection point. Our theoretical evidence based on the ELF topology shows that the C-O bond is formed on the ground-state surface (via C-O attack) returning from the S 1 surface accompanied by 1,4-singlet diradical formation. Read More

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September 2021

Synthesis and Mechanistic Insights of the Formation of 3-Hydroxyquinolin-2-ones including Viridicatin from 2-Chloro-,3-diaryloxirane-2-carboxamides under Acid-Catalyzed Rearrangements.

J Org Chem 2021 Sep 10. Epub 2021 Sep 10.

Mulliken Center for Theoretical Chemistry University of Bonn, Beringstr. 4, 53115 Bonn, Germany.

-Benzyl-2-chloro-,3-diaryloxirane-2-carboxamides, easily obtained from aromatic aldehydes and anilides of dichloroacetic acid under Darzens condensation conditions, proved to be excellent starting compounds for the synthesis of 3-hydroxyindolin-2-ones, cyclohepto[]pyrrole-2,3-diones, and 1-azaspiro[4.5]deca-3,6,9-triene-2-ones via the C(sp)-C(sp) bond formation in the first case and C(sp)-C(sp) bond formation in the second and third cases. Under optimized reaction conditions, 3-hydroxyindolin-2-ones are obtained in a one-pot process, which involves the treatment of -benzyl-2-chloro-,3-diaryloxirane-2-carboxamides with CFCOH or AcOH/HSO. Read More

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September 2021

A Flexible Synthetic Approach to Fluorescent Chromeno[4,3-b]pyridines and Pyrano[3,2-c]chromenes from Electron-Deficient 3-Vinylchromones.

Chempluschem 2021 Aug 19;86(9):1256-1266. Epub 2021 Aug 19.

Organic Chemistry Department, Saint-Petersburg State Chemical Pharmaceutical University, Prof. Popov st., 14, Saint-Petersburg, 197376, Russia.

We report a flexible approach to the synthesis of phenanthrene-like heterocycles through organocatalytic ANRORC (Addition of the Nucleophile, Ring Opening, and Ring Closure) reaction of electron-deficient 3-vinylchromones with cyanoacetamide. Addition of highly basic DBU (1,8-diazabicyclo[5.4. Read More

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A one-pot ring-closure and ring-opening sequence for the cascade synthesis of dihydrofurofurans and functionalized furans.

Org Biomol Chem 2021 Sep 16;19(34):7409-7419. Epub 2021 Aug 16.

Department of Image Science and Engineering, Pukyong National University, Busan 608-737, Republic of Korea.

We have developed a simple novel ring-closure and ring-opening pathway using an organo-base system for the synthesis of highly substituted dihydrofurofuran and furan frameworks via a triethylamine-catalyzed one-pot three-component reaction. The protocol involved a Knoevenagel and Michael adduct via Paal-Knorr cyclization with aromatic/aliphatic glyoxal and 2-cyanoacetophenone under mild and heating conditions with excellent yields through a simple filtration method. The merits of this methodology, including the use of easily available feedstocks and an inexpensive catalyst, Gram-scale synthesis, wide functional group tolerance, an open-air reaction setup, and no need for workup and column-chromatography procedures, make the developed methodology a practical way to access dihydrofurofurans and functionalized furans. Read More

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September 2021

Computational insight into biotransformation of halophenols by cytochrome P450: Mechanism and reactivity for epoxidation.

Chemosphere 2021 Jul 29;286(Pt 2):131708. Epub 2021 Jul 29.

College of Geography and Environmental Sciences, Zhejiang Normal University, Yingbin Avenue 688, 321004, Jinhua, China. Electronic address:

Halophenols (XPs) have aroused great interests due to their high toxicity and low biodegradability. Previous experimental studies have shown that XPs can be catalytically transformed into epoxides and haloquinones by cytochrome P450 enzymes (CYPs). However, these metabolites have never been detected directly. Read More

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Screening for New Pathways in Atmospheric Oxidation Chemistry with Automated Mechanism Generation.

J Phys Chem A 2021 Aug 4;125(31):6772-6788. Epub 2021 Aug 4.

Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.

In the Earth's atmosphere, reactive organic carbon undergoes oxidation via a highly complex, multigeneration process, with implications for air quality and climate. Decades of experimental and theoretical studies, primarily on the reactions of hydrocarbons, have led to a canonical understanding of how gas-phase oxidation of organic compounds takes place. Recent research has brought to light a number of examples where the presence of certain functional groups opens up reaction pathways for key radical intermediates, including alkyl radicals, alkoxy radicals, and peroxy radicals, that are substantially different from traditional oxidation mechanisms. Read More

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Enyne Amides to Fused Pyridones: Scope and Limitations.

J Org Chem 2021 Aug 2. Epub 2021 Aug 2.

Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, United States.

Herein we present an investigation into the scope and mechanism for the synthesis of cyclopentyl and heterocyclic fused pyridones from the corresponding enyne amides. In the presence of a secondary amine, cyclization proceeds smoothly to form 5,6-bicyclic pyridones in 12-90% yield. The cyclization fails with enyne amides of six-membered and larger ring systems. Read More

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Silinanyl Rhodamines and Silinanyl Fluoresceins for Super-Resolution Microscopy.

J Phys Chem B 2021 Aug 30;125(31):8703-8711. Epub 2021 Jul 30.

Central Research Laboratories, Sysmex Corporation, Takatsukadai 4-4-4, Nishi-ku, Kobe, Hyogo 651-2271, Japan.

Single-molecule localization microscopy (SMLM) enables the visualization of biomolecules at unprecedented resolution and requires control of the fluorescent blinking (ON/OFF) states of fluorophores to detect single-molecule fluorescence without overlapping of the signals. Although SMLM probes based on the intramolecular spirocyclization of Si-xanthene fluorophores have been developed, fluorophores with lower ON/OFF ratios are required for SMLM visualization of high-density structures. Here, we describe a silinane structure that lowers the ON/OFF ratio of Si-xanthene fluorophores. Read More

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A structure activity relationship for ring closure reactions in unsaturated alkylperoxy radicals.

Phys Chem Chem Phys 2021 Aug;23(31):16564-16576

Institute for Energy and Climate Research: IEK-8: Troposphere, Forschungszentrum Jülich GmbH, Jülich, Germany.

Terpenoids are an important class of multi-unsaturated volatile organic compounds emitted to the atmosphere. During their oxidation in the troposphere, unsaturated peroxy radicals are formed, which may undergo ring closure reactions by an addition of the radical oxygen atom on either of the carbons in the C[double bond, length as m-dash]C double bond. This study describes a quantum chemical and theoretical kinetic study of the rate of ring closure, finding that the reactions are comparatively fast with rates often exceeding 1 s-1 at room temperature, making these reactions competitive in low-NOx environments and allowing for continued autoxidation by ring closure. Read More

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Effect of metallosupramolecular polymer concentration on the synthesis of poly[]catenanes.

Chem Sci 2021 Jul 26;12(25):8722-8730. Epub 2021 May 26.

Department of Chemistry, University of Chicago Chicago IL USA.

Poly[]catenanes are a class of polymers that are composed entirely of interlocked rings. One synthetic route to these polymers involves the formation of a metallosupramolecular polymer (MSP) that consists of alternating units of macrocyclic and linear thread components. Ring closure of the thread components has been shown to yield a mixture of cyclic, linear, and branched poly[]catenanes. Read More

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Asymmetric Synthesis of Fluoro, Fluoromethyl, Difluoromethyl, and Trifluoromethylcyclopropanes.

Acc Chem Res 2021 07 7;54(14):2969-2990. Epub 2021 Jul 7.

Normandie University, INSA Rouen, UNIROUEN, CNRS, COBRA UMR 6014, 7600 Rouen, France.

Fluorine-containing cyclopropanes are a subclass of cyclopropane derivatives that have generated considerable interest in medicinal chemistry for several decades. The replacement of a cyclopropane C-H or C-CH bond with fluorine or a fluorinated group (such as CF or CFH) can lead sometimes to synergistic effects in terms of biological activity and improved metabolic profile of a cyclopropane containing bioactive compound. In this context, the preparation of fluoro-, difluoromethyl-, or trifluoromethyl-cyclopropane is particularly attractive and important but quite challenging considering the unique electronic properties that result from the incorporation of a fluorine atom into a substrate or a reagent. Read More

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A Photo- and Redox-Driven Two-Directional Terthiazole-Based Switch: A Combined Experimental and Computational Investigation.

Chemistry 2021 Sep 28;27(50):12866-12876. Epub 2021 Jul 28.

Université Paris-Saclay, CNRS, Institut de Chimie Moléculaire et des Matériaux d'Orsay, 91405, Orsay, France.

Terthiazoles with redox-active substituents like an N-methyl pyridinium group and ferrocene have been synthesized and their photo- and electro-chromic behaviors were investigated. The presence of two lateral N-methyl pyridinium substituents in the structure of terthiazole proved to be effective in inducing not only the reductive ring-closure of the terthiazole core but also its oxidative ring-opening reaction, leading to the first terarylene-based switch able to fully operate both photochemically and electrochemically. Moreover, the large increase in the redox potential between its open and closed form (700 mV) means that a part of the photon energy necessary to trigger the cyclization is stored in the form of chemical potential available for other works. Read More

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September 2021

Highly Regioselective Tandem Reaction of Ene-Yne-Oxazolones Induced by -Phosphonates: Construction of Phosphinylindane Derivatives.

J Org Chem 2021 07 2;86(14):9360-9383. Epub 2021 Jul 2.

Laboratory of Medicinal Chemistry, Chulabhorn Research Institute, Laksi, Bangkok 10210, Thailand.

A highly regioselective divergent approach for the phosphine-containing indane/indene derivatives from the ene-yne-oxazolone precursors was reported. An insight into the reaction mechanism involving the phospha-1,4-addition followed by 5- ring closure with a concomitant C-P/C-C bond formation was also proposed. This promising protocol utilized -phosphonate as the phosphonating reagent in a silver-catalyzed or base-mediated cascade cyclization to construct the corresponding phosphorylated spiroindenoxazolones and amidoindenes, respectively, in good yields (up to 88% yield). Read More

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Atmospheric Ring-Closure and Dehydration Reactions of 1,4-Hydroxycarbonyls in the Gas Phase: The Impact of Catalysts.

J Phys Chem A 2021 Jul 30;125(27):5963-5975. Epub 2021 Jun 30.

Department of Chemistry and Biochemistry, University of California-San Diego, La Jolla, California 92093, United States.

1,4-Hydroxycarbonyls can potentially undergo sequential reactions involving cyclization followed by dehydration to form dihydrofurans. As dihydrofurans contain a double bond, they are highly reactive toward atmospheric oxidants such as OH, O, and NO. In the present study, we use ab initio calculations to examine the impact of various atmospheric catalysts on the energetics and kinetics of the gas-phase cyclization and dehydration reaction steps associated with 4-hydroxybutanal, a prototypical 1,4-hydroxycarbonyl molecule. Read More

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Intramolecular Friedel-Crafts alkylation with a silylium-ion-activated cyclopropyl group: formation of tricyclic ring systems from benzyl-substituted vinylcyclopropanes and hydrosilanes.

Chem Sci 2020 Oct 29;12(2):569-575. Epub 2020 Oct 29.

Institut für Chemie, Technische Universität Berlin Strasse des 17. Juni 115 10623 Berlin Germany

A trityl-cation-initiated annulation of benzyl-substituted vinylcyclopropanes (VCPs) with hydrosilanes is reported. Two Si-C(sp) bonds and one C(sp)-C(sp) bond are formed in this process where an intramolecular 6- Friedel-Crafts alkylation of a silylium-ion-activated cyclopropane ring is the rate-determining key step. The reaction mechanism is proposed based on computations and is in agreement with experimental observations. Read More

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October 2020

Diastereoselective Synthesis of Tetrabenzohydrofuran Spirooxindoles via Diethyl Phosphite-Mediated Coupling of Isatins with -Quinone Methides.

J Org Chem 2021 07 24;86(13):8630-8640. Epub 2021 Jun 24.

State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Weijin Road 94, Tianjin 300071, China.

Diethyl phosphite-initiated coupling of isatins with -quinone methides (-QMs) is reported. This reaction involves a cascade transformation initiated by base-promoted addition of phosphite to isatins, followed by [1,2]-phospha-Brook rearrangement. This generates α-phosphonyloxy enolates that are subsequently intercepted by -QMs and finally intramolecular ring closure. Read More

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A multicomponent tetrazolo indole synthesis.

Chem Commun (Camb) 2021 Jul;57(54):6652-6655

University of Groningen, Department of Pharmacy, Drug Design group, Groningen, The Netherlands.

The ubiquitous presence of the indole fragment in natural products and drugs asks for ever novel syntheses. We report an unprecedented mild, two-step synthesis of 2-tetrazolo substituted indoles based on the Ugi-tetrazole reaction combined with an acidic ring closure. A gram-scale synthesis, a bioactive compound and further transformations were performed. Read More

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Cayley Graphs of Semigroups Applied to Atom Tracking in Chemistry.

J Comput Biol 2021 Jul 11;28(7):701-715. Epub 2021 Jun 11.

Department of Mathematics and Computer Science, University of Southern Denmark, Odense, Denmark.

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Accelerated Discovery of α-Cyanodiarylethene Photoswitches.

J Am Chem Soc 2021 Jun 11;143(24):9162-9168. Epub 2021 Jun 11.

DWI-Leibniz Institute for Interactive Materials & Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, Forckenbeckstrasse 50, Aachen 52074, Germany.

Cyanodiarylethene chromophores are able to undergo constitutional exchange via dynamic covalent chemistry (DCC). During this process, the central ethylene bridge of the molecular scaffold can be broken and thereby enables the assembly of a new combination of aryl moieties around the reformed ethylene bridge. The reversible C═C double bond exchange has exemplarily been investigated using α-cyanostilbenes. Read More

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B(CF)-Catalyzed Diastereoselective Formal (4 + 1)-Cycloaddition of Vinylcyclopropanes and EtSiH.

Org Lett 2021 Jun 2;23(12):4834-4837. Epub 2021 Jun 2.

Institut für Chemie, Technische Universität Berlin, Strasse des 17. Juni 115, 10623 Berlin, Germany.

A formal (4 + 1)-cycloaddition of vinylcyclopropanes and EtSiH to afford 3,4-disubstituted silolanes is reported. The reaction sequence commences with the known B(CF)-catalyzed alkene hydrosilylation with dihydrosilanes. Cleavage of the remaining Si-H bond in the hydrosilylation product assisted by B(CF) leads to formation of a cyclopropane-stabilized silylium ion. Read More

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Designing Force Probes Based on Reversible 6π-Electrocyclizations in Polyenes Using Quantum Chemical Calculations.

J Org Chem 2021 Jun 14;86(11):7477-7489. Epub 2021 May 14.

Eenheid Algemene Chemie (ALGC), Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050 Brussels, Belgium.

The conjugated π-system in polyenes can be interrupted by electrocyclic ring-closure reactions. In this work, this 6π-electrocylization is shown by means of density functional calculations to be reversible by the application of an external mechanical pulling force at the terminal ends of the interrupted polyene chain. The test systems were constrained in a fused ring system, thus locking the orientation of three π-bonds and generally promoting 6π-electrocyclic ring-closure reactions. Read More

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Phosphetes via Transition Metal Free Ring Closure - Taking the Proper Turn at a Thermodynamic Crossing.

Chemistry 2021 Jul 2;27(38):9782-9790. Epub 2021 Jun 2.

Institute for Chemistry and CINSaT, University of Kassel, Heinrich Plett-Straße 40, 34132, Kassel, Germany.

A transition metal free route to phosphetes featuring an exocyclic alkene unit is presented. In this approach phosphanides are added to a variety of diynes generating phosphaallylic intermediates which depending on the reaction conditions transform either to phosphetes or the corresponding phospholes. Investigation of the reaction mechanism by combined quantum chemical and experimental means identifies phosphole formation as thermodynamically controlled reaction path, whereas kinetic control furnishes the corresponding phosphetes. Read More

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-Diels-Alder Reactions of In Situ-Generated Azoalkenes with Thioketones; Experimental and Theoretical Studies.

Molecules 2021 Apr 27;26(9). Epub 2021 Apr 27.

Institut für Chemie und Biochemie, Freie Universität Berlin, Takustrasse 3, 14195 Berlin, Germany.

The -Diels-Alder reactions of in situ-generated azoalkenes with thioketones were shown to offer a straightforward method for an efficient and regioselective synthesis of scarcely known N-substituted 1,3,4-thiadiazine derivatives. The scope of the method was fairly broad, allowing the use of a series of aryl-, ferrocenyl-, and alkyl-substituted thioketones. However, in the case of N-tosyl-substituted cycloadducts derived from 1-thioxo-2,2,4,4-tetramethylcyclobutan-3-one and the structurally analogous 1,3-dithione, a more complicated pathway was observed. Read More

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Enantioselective Construction of the Cycl[3.2.2]azine Core via Organocatalytic [12 + 2] Cycloadditions.

J Am Chem Soc 2021 04 19;143(16):6140-6151. Epub 2021 Apr 19.

Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark.

The first enantioselective [12 + 2] cycloaddition has been developed for the construction of a chiral cycl[3.2.2]azine core, a tricyclic moiety with a central ring-junction nitrogen atom, by an operationally simple one-step organocatalytic process. Read More

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Reaction of 3-Oxa-2-oxobicyclo[4.2.0]oct-4-ene-1-carboxylate with Dimethylsulfoxonium Methylide.

Chem Pharm Bull (Tokyo) 2021 ;69(4):391-399

Kyoto Pharmaceutical University.

We have been interested in the reactivities of small-ring compounds and have reported reactions that proceed through cyclopropane intermediates starting from coumarin derivatives bearing an electron-withdrawing group at the 3-position or 2-oxo-2H-pyran-3-carboxylate derivatives and dimethylsulfoxonium methylide. This time, the reaction between 3-oxa-2-oxobicyclo[4.2. Read More

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Diarylethene-Powered Light-Induced Folding of Supramolecular Polymers.

J Am Chem Soc 2021 04 23;143(15):5845-5854. Epub 2021 Mar 23.

Institute for Global Prominent Research (IGPR), Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.

Helical folding of randomly coiled linear polymers is an essential organization process not only for biological polypeptides but also for synthetic functional polymers. Realization of this dynamic process in supramolecular polymers (SPs) is, however, a formidable challenge because of their inherent lability of main chains upon changing an external environment that can drive the folding process (e.g. Read More

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Spin-forbidden heavy-atom tunneling in the ring-closure of triplet cyclopentane-1,3-diyl.

Phys Chem Chem Phys 2021 Mar;23(10):5797-5803

University of Coimbra, CQC, Department of Chemistry, 3004-535 Coimbra, Portugal.

In 1975, Buchwalter and Closs reported one of the first examples of heavy-atom quantum mechanical tunneling (QMT) by studying the ring closure of triplet cyclopentane-1,3-diyl to singlet bicyclo[2.1.0]pentane in cryogenic glasses. Read More

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Effective Synthesis of Ladder-type Oligo(-aniline)s and Poly(-aniline)s via Intramolecular SAr Reaction.

Org Lett 2021 Mar 26;23(6):2217-2221. Epub 2021 Feb 26.

College of Chemistry and Environmental Science, Hebei University, Baoding 071002, P. R. China.

Symmetric ladder-type oligo(-aniline)s and poly(-aniline)s were successfully synthesized by an intramolecular ring closure in a highly efficient SAr reaction from oligo(-phenylene)s and poly(-phenylene)s with fluorine (F) and secondary amine (NH) groups. Unlike Cadogan ring closure, the newly designed cyclization reaction will not produce a mixture of symmetric and nonsymmetric structures. Moreover, the introduction of the F atom does not hinder Suzuki polymerization. Read More

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Insight into intramolecular chemical structure modifications by on-surface reaction using photoemission tomography.

Chem Commun (Camb) 2021 Mar 24;57(24):3050-3053. Epub 2021 Feb 24.

Peter Grünberg Institute (PGI-6), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany.

The sensitivity of photoemission tomography (PT) to directly probe single molecule on-surface intramolecular reactions will be shown here. PT application in the study of molecules possessing peripheral ligands and structural flexibility is tested on the temperature-induced dehydrogenation intramolecular reaction on Ag(100), leading from CoOEP to the final product CoTBP. Along with the ring-closure reaction, the electronic occupancy and energy level alignment of the frontier orbitals, as well as the oxidation state of the metal ion, are elucidated for both the CoOEP and CoTBP systems. Read More

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Calcium catalyzed enantioselective intramolecular alkene hydroamination with chiral -symmetric bis-amide ligands.

Dalton Trans 2021 Mar;50(9):3178-3185

Inorganic and Organometallic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 1, 91058 Erlangen, Germany.

The chiral building block (R)-(+)-2,2'-diamino-1,1'-binaphthyl, (R)-BINAM, which is often used as backbone in privileged enantioselective catalysts, was converted to a series of N-substituted proligands R1-H2 (R = CH2tBu, C(H)Ph2, PPh2, dibenzosuberane, 8-quinoline). After double deprotonation with strong Mg or Ca bases, a series of alkaline earth (Ae) metal catalysts R1-Ae·(THF)n was obtained. Crystal structures of these C2-symmetric catalysts have been analyzed by quadrant models which show that the ligands with C(H)Ph2, dibenzosuberane and 8-quinoline substituents should give the best steric discrimination for the enantioselective intramolecular alkene hydroamination (IAH) of the aminoalkenes H2C[double bond, length as m-dash]CHCH2CR'2CH2NH2 (CR'2 = CPh2, CCy or CMe2). Read More

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