Rhodium/Amine Dual Catalytic System for Reassembling C≡C Bonds of Conjugated Alkynes with Cyclopropenes via Cutting/Insertion Cascade
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Abstract:
Amines are powerful organocatalysts that are well-documented in catalyzing carbonyl compounds to realize transformations. However, they are rarely applied in alkyne activations. Herein, we disclose an efficient amine/Rh(II) dual catalytic system to reassemble the C≡C bond of conjugated alkynes with cyclopropenes, which enables construction of α-vinyldicarbonyl derivatives under very mild reaction conditions. Vinyl cyclopropylamines might be involved as key intermediates through ring-opening of cyclopropenes, catalytic amination of alkynes, and tandem cyclopropantion sequences in high atom and step-economies. This formal cutting/insertion cascade platform is compatible with a broad substrate scope including complex natural and unnatural molecules for late-stage functionalization.Keywords:
Alkyne
Cascade reaction
Triple bond
Atom economy
Tandem
Surface Modification
The cascade reactions of alkynylchromium Fischer carbene complexes featuring an additional pendant triple bond are presented. The processes are triggered by [2 + 2], [3 + 2], and [4 + 2] cycloadditions. Depending on the substitution of the appended triple bond, and the nature of the triggering cycloaddition reaction, different polycyclic compounds can be obtained. Predictable results are obtained in most of the cases when the Fischer carbene complex bears a TMS-substituted alkyne. In these cases, naphtalene derivatives substituted with a TMS-ketene are obtained in sequences that involve alkyne exo insertion followed by CO migration. However, the reaction with a carbene complex featuring a terminal alkyne follows an alternative reaction pathway, in which the nucleophilic attack of the triple bond at the carbenic carbon forms a benzo[7]annulene. Mechanistic interpretations based on DFT calculations are provided.
Alkyne
Triple bond
Annulene
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Alkyne
Markovnikov's rule
Triple bond
Methyl iodide
Carbon atom
Derivative (finance)
Oxidative addition
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Vinyl chlorides can be effectively prepared via alkyne hydrochlorination catalyzed by the [Cp*RuCl(cod)]/PPh3 system. The reaction mechanism has been elucidated by density functional theory calculations. Different from the previously proposed pathway (oxidative addition, alkyne coordination, H-/Cl-transfer via inner addition, and reductive elimination), the calculation results indicate that HCl favorably attacks the alkyne stepwise from the outer coordination sphere of the Ru center. The reaction is essentially the electrophilic addition of HCl to alkyne. Therefore, the proton tends to attack the more negatively charged carbon of the C–C triple bond, leading to the Markovnikov product.
Alkyne
Triple bond
Markovnikov's rule
Reductive elimination
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An efficient approach for the synthesis of pyrazolopyridines containing the aminochromane motif through a base-catalyzed cyclization reaction is reported. The synthesis was carried out through a three-component reaction of (arylhydrazono)methyl-4H-chromen-4-one, malononitrile, primary amines in the presence of Et3N at room temperature. However, carrying out the reaction under the same conditions without base led to a fused chromanyl-cyanopyridine. High selectivity, high atom economy, and good to high yields in addition to mild reaction conditions are the advantages of this approach.
Cascade reaction
Atom economy
Domino
Reaction conditions
Base (topology)
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One-pot reactions based on catalytic isomerization of alkenes not only offer the inherent advantages of atom-, step- and redox-economy but also enable the preparation of value-added products that would be difficult to access by conventional methods.
Domino
Alkene
Cascade reaction
Tandem
Atom economy
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Abstract A mild and practical Rh(III)‐catalyzed C 7 –H amination of indolines has been described, which allows the synthesis of a variety of 7‐amino‐substituted indolines with good functional group tolerance and high atom economy. Notably, nitrosobenzenes serve as nitrogen source in this transformation, and therefore behave environmentally friendly for C−N bond constructions.
Nitrogen atom
Functional group
Atom economy
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Alkyne
Triple bond
Bond cleavage
Metal carbonyl
Cleavage (geology)
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Chemoselectivity
Atom economy
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Abstract Abstract . We report herein the synthesis of [7,5]‐fused bicyclic acetals, also named furooxepines through a gold(I)‐catalyzed domino reaction. During this transformation, two molecules of homopropargyl alcohol react together, in a sequence including an intramolecular hydroalkoxylation, condensation, a 1,6‐enyne cycloisomerization, acetalization and an isomerization. This gold(I)‐catalyzed domino reaction allow the formation of three bonds, two heterocycles and a tetrasubstituted carbon stereocenters in a one‐step operation with 100% atom economy. Post‐functionalizations allow the formation of tetrahydrofurans. magnified image
Cycloisomerization
Stereocenter
Domino
Cascade reaction
Enyne
Atom economy
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Abstract We present a silver‐catalyzed reaction of acceptor‐enynals with alkynes to assemble tetracyclic framework of fluorenols efficiently, in which the reaction was proposed to proceed through an unfavorable 6 ‐endo‐dig cyclization, followed by a tandem [4+2] cycloaddition/Friedel–Crafts reaction. The reaction could be conducted in one pot for diaryl alkynes substrates. For terminal aryl alkyne or arylalkyl alkyne substrates, the Friedel–Crafts reaction has to be performed in the absence of alkynes. The control reactions demonstrated that there was competition between [Ag]⋅⋅⋅alkyne and [Ag]⋅⋅⋅O=CR 2 .
Alkyne
Friedel–Crafts reaction
Cascade reaction
Tandem
Acceptor
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