1,721,001 research outputs found
Iridium(III)-catalyzed direct C-7 amination of indolines with organic azides
No full textIridium-catalyzed regioselective C-7 amination
of indolines has been achieved with organic azides as a facile
nitrogen source. The developed procedure is convenient to
perform even at room temperature and applicable to a wide
range of substrates with high catalytic activity. Various types of
organic azides (sulfonyl, aryl, and alkyl derivatives) were all successfully reacted under the present conditions as the viable
reactant. Furthermore, indoline substrates bearing easily removable N-protecting groups such as N-Boc or N-Cbz could readily
be employed, highlighting the synthetic utility of this methodology.626411sciescopu
Direct C-H amination of arenes with alkyl azides under rhodium catalysis
No full textNew horizons in the utility of azides: The rhodium-catalyzed intermolecular direct C-H amination of arenes with alkyl azides provides a convenient route to N-alkyl anilines (see scheme; DG=directing group). Alkyl azides with a wide range of functional groups reacted readily with various substrates, including benzamides, aromatic ketones, and flavones. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.11181201sciescopu
Cp∗Ir(III)-Catalyzed Mild and Broad C-H Arylation of Arenes and Alkenes with Aryldiazonium Salts Leading to the External Oxidant-Free Approach
No full textReported herein is the development of Cp*Ir(III)-
catalyzed direct C−H arylation of arenes and alkenes using
aryldiazonium tetrafluoroborates, the use of which as an aryl precursor
and also as an oxidant via C−N2 bond cleavage was a key to success in
achieving a mild and external oxidant-free procedure. Mechanistic
experiments and DFT calculations revealed the turnover-limiting step
to be closely related to the formation of an Ir(V)-aryl intermediate
rather than the presupposed C−H cleavage. Under the developed mild
arylation conditions, a wide range of benzamides were smoothly arylated. In addition, synthetic utility of the current C−H
arylation procedure was also demonstrated successfully for the (Z)-selective arylation of enamides and C8-selective reaction of
quinoline N-oxides. © 2015 American Chemical Society157571sciescopu
Transition-metal-catalyzed C-N bond forming reactions using organic azides as the nitrogen source: A journey for the mild and versatile C-H amination
No full textConspectus Owing to the prevalence of nitrogen-containing compounds in functional materials, natural products and important pharmaceutical agents, chemists have actively searched for the development of efficient and selective methodologies allowing for the facile construction of carbon-nitrogen bonds. While metal-catalyzed C-N cross-coupling reactions have been established as one of the most general protocols for C-N bond formation, these methods require starting materials equipped with functional groups such as (hetero)aryl halides or their equivalents, thus generating stoichiometric amounts of halide salts as byproducts. To address this aspect, a transition-metal-catalyzed direct C-H amination approach has emerged as a step- and atom-economical alternative to the conventional C-N cross-coupling reactions. However, despite the significant recent advances in metal-mediated direct C-H amination reactions, most available procedures need harsh conditions requiring stoichiometric external oxidants. In this context, we were curious to see whether a transition-metal-catalyzed mild C-H amination protocol could be achieved using organic azides as the amino source. We envisaged that a dual role of organic azides as an environmentally benign amino source and also as an internal oxidant via N-N2 bond cleavage would be key to develop efficient C-H amination reactions employing azides. An additional advantage of this approach was anticipated: that a sole byproduct is molecular nitrogen (N2) under the perspective catalytic conditions.This Account mainly describes our research efforts on the development of rhodium- and iridium-catalyzed direct C-H amination reactions with organic azides. Under our initially optimized Rh(III)-catalyzed amination conditions, not only sulfonyl azides but also aryl- and alkyl azides could be utilized as facile amino sources in reaction with various types of C(sp2)-H bonds bearing such directing groups as pyridine, amide, or ketoxime. More recently, a new catalyst system using Ir(III) species was developed for the direct C-H amidation of arenes and alkenes with acyl azides under exceptionally mild conditions. As a natural extension, amidation of primary C(sp3)-H bonds could also be realized on the basis of the superior activity of the Cp∗Ir(III) catalyst. Mechanistic investigations revealed that a catalytic cycle is operated mainly in three stages: (i) chelation-assisted metallacycle formation via C-H bond cleavage; (ii) C-N bond formation through the in situ generation of a metal-nitrenoid intermediate followed by the insertion of an imido moiety to the metal carbon bond; (iii) product release via protodemetalation with the concomitant catalyst regeneration. In addition, this Account also summarizes the recent advances in the ruthenium- and cobalt-catalyzed amination reactions using organic azides, developed by our own and other groups. Comparative studies on the relative performance of those catalytic systems are briefly described. © 2015 American Chemical Society13753841sciescopu
Iridium-Catalyzed C-H Amination with Anilines at Room Temperature: Compatibility of Iridacycles with External Oxidants
No full textDescribed herein is the development of an iridium-catalyzed direct C-H amination of benzamides with anilines at room temperature, representing a unique example of an Ir catalyst system that is compatible with external oxidants. Mechanistic details, such as the isolation and characterization of key iridacycle intermediates, are also discussed. © 2014 American Chemical Society.10911011sciescopu
Rh(III)- and Ir(III)-catalyzed direct C-H bond transformations to carbon-heteroatom bonds
No full textThe direct manipulation of C-H bonds is now a powerful tool in chemical synthesis. In achieving the current high standard of research progresses, Rh(III) and Ir(III) complexes played an important role to understand the nature of C-H bond activation. While numerous stoichiometric reactions of hydrocarbons with Rh (III) or Ir(III) complexes were scrutinized, their use in catalytic transformations has been relatively undeveloped until recently. Given their outstanding reactivity in C-H activation, they are highly promising candidates for inducing mild C-H functionalizations. In spite of a short development history, numerous contributions from leading research groups made big strides in highly efficient and selective C-H bond transformations for the C-C and C-heteroatom bond formation. In this report, we specifically focus on the Rh(III)- or Ir(III)-mediated direct C-H functionalizations for the C-heteroatom bond formation that is now a rapidly growing area. This report presents the current status of such catalytic systems including scope of substrates and coupling partners as well as brief mechanistic descriptions. © Springer International Publishing Switzerland 2015133411sciescopu
Orthogonal reactivity of acyl azides in C-H activation: Dichotomy between C-C and C-N amidations based on catalyst systems
No full textThe dual reactivity of acyl azides was utilized successfully in C-H activation by the choice of catalyst systems: while selective C-C amidation was achieved under thermal Rh catalysis, a Ru catalyst was found to mediate direct C-N amidation also highly selectively. Investigations of the mechanistic dichotomy between two catalytic systems are also presented. © 2014 American Chemical Society.535411sciescopu
Chelation-Assisted Hydroesterification of Alkenes: New Ruthenium Catalyst Systems and Ligand Effects
No full textNew types of ruthenium catalysts were developed for the chelation-assisted intermolecular olefin hydroesterification that employs 2-pyridylmethyl formate as an ester source. Two classes of ligands, NHCs and phosphines, were found to facilitate the reaction delivering isomeric ester products (linear versus branched) with different ratios, thus allowing access to ligand-guided selective hydroesterification.242611sciescopu
Iridium-catalysed arylation of C-H bonds enabled by oxidatively induced reductive elimination
No full textDirect arylation of C-H bonds is in principle a powerful way of preparing value-added molecules that contain carbon-aryl fragments. Unfortunately, currently available synthetic methods are not sufficiently effective to be practical alternatives to conventional cross-coupling reactions. We propose that the main problem lies in the late portion of the catalytic cycle where reductive elimination gives the desired carbon-aryl bond. Accordingly, we have developed a strategy where the Ir(III) centre of the key intermediate is first oxidized to Ir(IV). Density functional theory calculations indicate that the barrier to reductive elimination is reduced by nearly 19 kcal mol-1 for this oxidized complex compared with that of its Ir(III) counterpart. Various experiments confirm this prediction, affording a new methodology capable of directly arylating C-H bonds at room temperature with a broad substrate scope and in good yields. This work highlights how the oxidation states of intermediates can be targeted deliberately to catalyse an otherwise impossible reaction. ©2018 Macmillan Publishers Limited, part of Springer Nature. (c) All rights reserve
Selective Synthesis of Silacycles by Borane-Catalyzed Domino Hydrosilylation of Proximal Unsaturated Bonds: Tunable Approach to 1,n-Diols
No full textThe tris(pentafluorophenyl)boron-catalyzed domino hydrosilylation of substrates carrying unsaturated functionalities in a proximal arrangement is presented to produce silacycles. Excellent levels of efficiency and selectivity were achieved in the cyclization by the deliberate choice of the hydrosilane reagents. The key to successful cyclic hydrosilylation is the reactivity enhancement of the second intramolecular hydrosilylation by a proximity effect. Not only dienes but also enones, enynes, ynones and enimines readily afford medium-sized silacycles under convenient and mild conditions. The cyclization proceeds with acceptable diastereoselectivity mainly controlled by the conformational bias towards inducing additional stereogenic centers. The silacycles obtained from this reaction were converted to 1,n-diols or 1,n-amino alcohols upon oxidation, thus rendering the present cyclization a powerful tool for accessing synthetically valuable building blocks. (Figure presented.). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei1
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