Branes Ending On Branes In A Tachyon Model

In a tachyon model proposed by Minahan and Zwiebach and derived in the boundary string field theory, we construct various new solutions which correspond to nontrivial brane configurations in string theory. Our solutions include Dp-D(p-2) bound states, (F, Dp) bound states, string junctions, D(p-2)-branes ending on a Dp-brane, D(p-2)-branes suspended between parallel Dp-branes and their non-commutative generalizations. We find the Bogomol'nyi bounds and the BPS equations for some of our solutions, and check the physical consistency of our solutions with the D-brane picture by looking at the distributions of their energies and RR-charges in space. We also give conjectures for a few other brane configurations.Comment: 19 pages, LaTeX, minor corrections and references adde

Catalytic Asymmetric Construction of CF₃-Substituted Chiral sp³ Carbon Centers

Due to the unique steric and electronic nature of the fluorine atom, organofluorine compounds have received significant attention in the fields of pharmaceuticals and agrochemicals. In particular, the CF3group is frequently found in biologically active compounds. However, compared to aryl- and alkenyl-CF3-containing molecules, the construction of sp3carbon-based alkyl-CF3-containing molecules, particularly via catalytic enantioselective synthesis, remains a considerable challenge in spite of their high potential in medicinal applications. This short review focuses on recent advances in this research area, and the reported strategies are categorized according to reaction types and starting substrates. In addition, chiral catalysts, substrate scope, and reaction mechanisms are briefly summarized. 1 Introduction 2 Stereoselective Introduction of a CF3Group 2.1 Nucleophilic Addition to Carbonyls and Imines 2.2 Electrophilic Substitution at the α Position of Carbonyls 2.3 Allylic Nucleophilic Substitution 3 Stereoselective Functionalization of CF3-Substituted Molecules 3.1 Electrophilic Substitution of α-CF3Carbonyls 3.2 Substitution of α-Halo CF3Compounds 3.3 Addition-Type Reactions with CF3-Substituted Alkenes 4 Conclusion and Outlook.This is an Accepted Manuscript of an article published by Thieme Publishing Group in Journal Title on Publication Date, available online at https://doi.org/10.1055/a-1833-8813

Copper-Catalyzed Electrophilic Amination: An Umpolung Strategy for New CN Bond Formations

The nitrogen atom is ubiquitous in bioactive molecules and functional materials, and the development of new CN bond forming strategies is thus one of the long-standing research subjects in the synthetic community. This account describes the nitrogen-umpolung-enabled copper-catalyzed highly chemo- and stereoselective amination protocols developed by the author’s research group. Starting from the CH amination, electrophilic amination of stable organoboron and organosilicon compounds, aminoboration/hydroamination of alkenes, and their applications to the synthesis of functionality-rich alkylamines are shown. The reaction design, concept, and substrate scope are briefly summarized

Mesure de température par pyrométrie 2D à bande spectrale et pyrométrie spectrale de métaux chauffés par laser dans un environnement fortement oxydant

La calibration et la validation de deux techniques de mesure de température complémentaires basées toutes les deux sur la pyrométrie optique (pyrométrie 2D monobande et pyrométrie spectrale), utilisables dans le cadre de l'étude des métaux chauffés dans des conditions hautement oxydantes et plus généralement au cours des procédés laser sur des métaux dans la gamme de température 2000-4000 K ont été réalisées. Une bonne correspondance des résultats des deux méthodes est obtenue lorsque l'émissivité de l'objet est connue et varie peu, mais seule la pyrométrie spectrale est performante lors de grandes variations d'émissivité, fournissant à la fois une mesure de température et d'émissivité au cours du procédé. Les incertitudes ont été calculées et représentent respectivement 6 et 3% dans une gamme de 1800 à 4500 K pour la pyrométrie 2D et la pyrométrie spectrale

Copper-mediated Trifluoromethylthiolation of Alkenyl Iodides with AgSCF₃

A copper-mediated trifluoromethylthiolation of alkenyl iodides with AgSCF₃ has been developed. CuSCF₃ species generated in-situ from a copper salt and AgSCF₃ can be coupled with alkenyl iodides to produce the corresponding trifluoromethylthioalkenes efficiently. The reaction conditions are compatible with various functional groups. Moreover, its scale-up synthesis is also possible to provide the desired trifluoromethylthiolated product even on a gram-scale

Hydroamination, Aminoboration, and Carboamination with Electrophilic Amination Reagents: Umpolung-Enabled Regio- and Stereoselective Synthesis of N-Containing Molecules from Alkenes and Alkynes

Nitrogen (N) is ubiquitously found in bioactive molecules, pharmaceutical agents, and organic functional materials. Accordingly, development of new C–N bond-forming catalysis has been one of the long-standing research subjects in synthetic organic chemistry. In this Perspective, recent advances in highly selective amination reactions with electrophilic amination reagents are described: by taking advantage of the concept of nitrogen umpolung, otherwise challenging aminofunctionalizations, such as hydroamination, aminoboration, and carboamination, of readily available feedstock-like alkenes and alkynes are possible, giving densely functionalized complex and often chiral alkylamines with high selectivity. The scope, limitations, and reaction mechanism are briefly summarized.Hirano K., Miura M.. Hydroamination, Aminoboration, and Carboamination with Electrophilic Amination Reagents: Umpolung-Enabled Regio- and Stereoselective Synthesis of N-Containing Molecules from Alkenes and Alkynes. Journal of the American Chemical Society. 144(2), 648-661, (2022), 19 January 2022; © 2022 American Chemical Society. https://doi.org/10.1021/jacs.1c12663

Copper-mediated Regioselective CH Cyanation of Phenols with Assistance of Bipyridine-type Bidentate Auxiliary

A Cu-mediated ortho-selective CH cyanation of phenols with ethyl cyanoformate as the cyano source has been developed. The key to success is the introduction of 4,4¤-di-tert-butyl-2,2¤-bipyridine (dtbpy) bidentate auxiliary on the phenol oxygen, which is easily attachable, detachable, and recyclable. The newly developed protocol is tolerant of several carbonyl functional groups, which are incompatible with previous Lewis-acid-promoted cyanation of phenols

Copper-Catalyzed Electrophilic Amination of gem-Diborylalkanes with Hydroxylamines Providing α-Aminoboronic Acid Derivatives

A copper-catalyzed electrophilic amination of gem-diborylalkanes with hydroxylamines has been developed. The key to its success is the use of the Me3Si-modified 1,2-bis(diphenylphosphino)benzene ligand. Additionally, the reactivity of neopentylglycol derivatives compared to that of commonly used pinacol-derived ones is found to be higher, particularly in the case of relatively sterically congested substrates. The copper catalysis presented here enables the first successful catalytic carbon-heteroatom bond forming reaction of gem-diborylalkanes to form the corresponding α-aminoboronic acid derivatives, which are of great interest in medicinal and pharmaceutical chemistry.Nishino S., Hirano K., Miura M.. Copper-Catalyzed Electrophilic Amination of gem-Diborylalkanes with Hydroxylamines Providing α-Aminoboronic Acid Derivatives. Organic Letters. 21(12), 4759-4762, (2019), 21 June 2019; © 2019 American Chemical Society. https://doi.org/10.1021/acs.orglett.9b01640

An umpolung-enabled copper-catalysed regioselective hydroamination approach to α-amino acids

A copper-catalysed regio- and stereoselective hydroamination of acrylates with hydrosilanes and hydroxylamines has been developed to afford the corresponding α-amino acids in good yields. The key to regioselectivity control is the use of hydroxylamine as an umpolung, electrophilic amination reagent. Additionally, a judicious choice of conditions involving the CsOPiv base and DTBM-dppbz ligand of remote steric hindrance enables the otherwise challenging C-N bond formation at the α position to the carbonyl. The point chirality at the β-position is successfully controlled by the Xyl-BINAP or DTBM-SEGPHOS chiral ligand with similarly remote steric bulkiness. The combination with the chiral auxiliary, (−)-8-phenylmenthol, also induces stereoselectivity at the α-position to form the optically active unnatural α-amino acids with two adjacent stereocentres.Nishino S., Miura M., Hirano K.. An umpolung-enabled copper-catalysed regioselective hydroamination approach to α-amino acids. Chemical Science 12, 11525 (2021); https://doi.org/10.1039/d1sc03692k