C–H alkylation reactions of indoles mediated by Pd(<scp>ii</scp>) and norbornene: applications and recent developments

Wegmann, Marcus; Henkel, Michael; Bach, Thorsten

doi:10.1039/c8ob01025k

Cited by 64 publications

(15 citation statements)

References 71 publications

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“…Recently, a direct C2 functionalization (mainly alkylation and arylation) of NH‐indoles and NH‐pyrroles was realized by Pd II /NBE cooperative catalysis. The Bach group initiated this research and made major contributions . In this Section, we have summarized the C2 functionalization of NH‐indoles and NH‐pyrroles by Pd II /NBE cooperative catalysis.…”

Section: C2 Functionalization Of Nh‐indoles and Nh‐pyrrolesmentioning

confidence: 99%

Palladium(II)‐Initiated Catellani‐Type Reactions

et al. 2019

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The Catellani reaction is known as a powerful strategy for the expeditious synthesis of highly substituted arenes and benzo‐fused rings, which are usually difficult to access through traditional cross‐coupling strategies. It utilizes the synergistic interplay of palladium and norbornene catalysis to facilitate sequential ortho C−H functionalization and ipso termination of aryl halides in a single operation. In classical Catellani‐type reactions, aryl halides are mainly used as the substrates, and a Pd0 catalyst is required to initiate the reaction. Nevertheless, recent advances showcase that Catellani‐type reactions can also be initiated by a PdII catalyst with different starting materials instead of aryl halides via different reaction mechanisms and under different conditions. This emerging concept of PdII/norbornene cooperative catalysis has significantly advanced Catellani‐type reactions, thus enabling future developments of this field. In this Minireview, PdII‐initiated Catellani‐type reactions and their application in the synthesis of bioactive molecules are summarized.

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Section: C2 Functionalization Of Nh‐indoles and Nh‐pyrrolesmentioning

confidence: 99%

Palladium(II)‐Initiated Catellani‐Type Reactions

et al. 2019

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“…The C2-selective indole alkylation method has been vividly embraced by the synthetic community and several applications to the synthesis of substituted indoles have been reported. 5 Since the alkylation at position C2 leaves both the indole nitrogen atom and the nucleophilic carbon atom C3 available for a second attack of an electrophile we wondered how 1,n-dibromoalkanes would behave in the Pd(II)-catalyzed alkylation reaction. Three dibromides (1,3-dibromopropane, 1,4-dibromobutane, and 1,5-dibromopentane) were chosen to probe the reactivity of indoles towards a twofold substitution.…”

Section: Scheme 1 Pd(ii)-catalyzed C2-selective Alkylation 4 Of Indomentioning

confidence: 99%

Annulation of Indoles with 1,n-Dibromoalkanes by a Pd(II)-Catalyzed and Norbornene-Mediated Reaction Cascade

Henkel¹,

Bach²

2019

Synthesis

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Employing 1,3-dibromopropane, 1,4-dibromobutane, and 1,5-dibromopentane as biselectrophiles, the annulation of indoles was probed in the presence of PdCl2(MeCN)2 as a catalyst and norbornene as a transpositional ligand. Ring formation to a five-membered ring was observed at positions C2 and N, while annulation of a six-membered ring occurred at positions C2 and C3. The latter cascade process was successfully applied to the direct synthesis of 1,2,3,4-tetrahydrocarbazoles from indoles (11 examples, 31–68% yield). Seven-membered-ring annulation was feasible by an initial coupling at positon C2 followed by alkylation at C3.

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“…This idea was inspired by the palladium/norbornene (Pd/NBE) cooperative catalysis (Fig. 1b) [12][13][14][15][16][17][18] , which was originally discovered by Catellani and co-workers 19 , and further implemented into a general synthetic methodology by the Lautens group 20,21 and many other research groups. In this chemistry, NBE reacts with an arylpalladium species to form an arylnorborylpalladacycle (ANP) intermediate, which then allows for sequential introduction of an electrophile (E + ) and a termination group (TG) at the ipso-and ortho-positions of the aryl ring, and finally regenerates NBE.…”

Section: Main: Introductionmentioning

confidence: 99%

Non-innocent hybrid cycloolefin ligands for palladium/olefin cooperative catalysis

Zheng

Jiao

2021

Preprint

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Catalyst design is a key research area in modern synthetic chemistry. Engineering of molecular catalysts in homogeneous catalysis brings about new catalytic modes that enable efficient synthetic transformations. In this regard, design of novel ligands for transition-metal catalysis have played a major role. Olefins have been emerging as a significant class of steering ligands in transition-metal catalysis, which are known to serve as innocent ligands that provide electronic and steric tuning of the metal center. However, it is unknown whether a distinct type of olefin ligand that contrasts the common innocent feature is possible. Here we show that a novel type of heteroatom-cycloolefin hybrid ligand functions as a non-innocent ligand in palladium catalysis, which exhibits covalent catalytic function that enables efficient ipso,orthodifunctionalization of iodoarenes. Detailed mechanistic study revealed that this ligand undergoes reversible covalent bonding between the substrate and the cycloolefin unit, which forms key organopalladium intermediates to enable new reactivity. Our results demonstrate a novel design concept that utilizes unstrained cycloolefin as a covalent catalytic module, opening an avenue to a more general transition metal/olefin cooperative catalysis.

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C–H alkylation reactions of indoles mediated by Pd(ii) and norbornene: applications and recent developments

Cited by 64 publications

References 71 publications

Palladium(II)‐Initiated Catellani‐Type Reactions

Palladium(II)‐Initiated Catellani‐Type Reactions

Annulation of Indoles with 1,n-Dibromoalkanes by a Pd(II)-Catalyzed and Norbornene-Mediated Reaction Cascade

Non-innocent hybrid cycloolefin ligands for palladium/olefin cooperative catalysis

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