Synthetic Approaches to Chiral Non-C
          2-symmetric N-Heterocyclic Carbene Precursors

Czerwiński, Paweł J.; Michalak, Michał

doi:10.1055/s-0037-1611733

Cited by 18 publications

(12 citation statements)

References 114 publications

(123 reference statements)

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“…The use of N‐heterocyclic carbenes (NHC) as ancillary ligands in various metal complexes has substantially contributed to the development of transition metal catalysis with major achievements for instance in ruthenium‐catalyzed olefin metathesis or palladium‐catalyzed cross coupling reactions 1–3 . Therefore, the design and the synthesis of chiral NHC ligands have attracted much attention during the last two decades 4–6 . The main strategies that have been investigated to design chiral monodentate NHC ligands can be divided into two categories: the introduction of a chiral element on the N ‐substituents (Figure 1A, structures A and B ) or the use of a chiral NHC backbone (structures C and D ).…”

Section: Introductionmentioning

confidence: 99%

Transition metal complexes bearing atropisomeric saturated NHC ligands

et al. 2021

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From achiral imidazolinium salts, chiral transition metal complexes containing an N-heterocyclic carbene (NHC) ligand were prepared (metal = palladium, copper, silver, gold, rhodium). Axial chirality in these complexes results from the formation of the metal-carbene bond leading to the restriction of rotation of dissymmetric N-aryl substituents about the C-N bond. When these complexes exhibited a sufficient configurational stability, a resolution by chiral highperformance liquid chromatography (HPLC) on preparative scale enabled isolation of enantiomers with excellent enantiopurities (>99% ee) and good yields. A study of the enantiomerization barriers revealed the effect of the backbone nature as well as the type of transition metal on its values. Nevertheless, the evaluation of palladium-based complexes in asymmetric intramolecular α-arylation of amides demonstrated that the ability to induce an enantioselectivity cannot be correlated to the configurational stability of the precatalysts.

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Section: Introductionmentioning

confidence: 99%

Transition metal complexes bearing atropisomeric saturated NHC ligands

et al. 2021

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“…In contrast, the rigid structure of NHCs (N-heterocyclic carbenes) provides an excellent opportunity to form stable gold complexes with a well-defined chiral environment, as was proven in the case of other metals, such as palladium [26][27][28][29], ruthenium [30][31][32][33] or copper [34][35][36][37][38][39][40][41][42]. Moreover, adequately planned structure of NHC ligands allows for tuning of their electronic and steric properties, which is not easily achievable in the case of phosphines [43,44].…”

Section: Introductionmentioning

confidence: 99%

Chiral N-heterocyclic Carbene Gold Complexes: Synthesis and Applications in Catalysis

Michalak

Kośnik

2019

Catalysts

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N-Heterocyclic carbenes have found many applications in modern metal catalysis, due to the formation of stable metal complexes, and organocatalysis. Among a myriad of N-heterocyclic carbene metal complexes, gold complexes have gained a lot of attention due to their unique propensity for the activation of carbon-carbon multiple bonds, allowing many useful transformations of alkynes, allenes, and alkenes, inaccessible by other metal complexes. The present review summarizes synthetic efforts towards the preparation of chiral N-heterocyclic gold(I) complexes exhibiting C 2 and C 1 symmetry, as well as their applications in enantioselective catalysis. Finally, the emerging area of rare gold(III) complexes and their preliminary usage in asymmetric catalysis is also presented. Scheme 3. The synthesis of a gold(I) complex from (R)-1-aminotetralin.An elegant approach to C2-symmetric gold(I) complexes was described by Czekelius et al. [72] (Scheme 4), inspired by previous Herrmann's work [73]. The synthetic approach involves chiral amines 24, readily available from the corresponding phenylacetic acid 22 via the Friedel-Crafts reaction of bromobenzene and fractional crystallization of the corresponding tartaric acid amine salt upon reductive amination. The resulting amine 24 was further formylated and subjected to Bischler-Napieralski cyclization to give 3-aryl-substituted dihydroisoquinoline 25. Subsequent reductive coupling afforded the basic diamine skeleton 26 into a single diastereomer, which appeared a perfect platform for structural ligand diversification via Suzuki coupling. The functionalized diamines 26 were then cyclized into imidazolium salts 27 with triethyl orthoformate to give the products with yields in the range of 49-94% (for selected examples, see Scheme 4). The formation of gold(I) complexes 28 was accomplished under rather unusual conditions, by the reaction of gold(I) chloride with a carbene generated by the action of KOtBu. Scheme 4. The synthesis of C2-symmetric gold(I) complexes accessible via a reductive coupling. The application of other chiral building blocks has recently been reported by the Toste group (Scheme 5) [74]. Besides chiral amines, amino alcohols 29 were also utilized in the synthesis of C2-Scheme 3. The synthesis of a gold(I) complex from (R)-1-aminotetralin.An elegant approach to C 2 -symmetric gold(I) complexes was described by Czekelius et al. [72] (Scheme 4), inspired by previous Herrmann's work [73]. The synthetic approach involves chiral amines 24, readily available from the corresponding phenylacetic acid 22 via the Friedel-Crafts reaction of bromobenzene and fractional crystallization of the corresponding tartaric acid amine salt upon reductive amination. The resulting amine 24 was further formylated and subjected to Bischler-Napieralski cyclization to give 3-aryl-substituted dihydroisoquinoline 25. Subsequent reductive coupling afforded the basic diamine skeleton 26 into a single diastereomer, which appeared a perfect platform for structural ligand diversification via Suzuki...

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“…The attempt on many traditional synthesis routes was in vain . After many experiments conducted, a successful route was listed in Scheme .…”

Section: Methodsmentioning

confidence: 99%

A Novel Bisoxazoline‐Imidazolium Salt in Ytterbium‐Catalyzed Asymmetric Reduction of Ketone

Zhai

Wang

et al. 2020

Eur J Org Chem

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Synthetic Approaches to Chiral Non-C 2-symmetric N-Heterocyclic Carbene Precursors

Cited by 18 publications

References 114 publications

Transition metal complexes bearing atropisomeric saturated NHC ligands

Transition metal complexes bearing atropisomeric saturated NHC ligands

Chiral N-heterocyclic Carbene Gold Complexes: Synthesis and Applications in Catalysis

A Novel Bisoxazoline‐Imidazolium Salt in Ytterbium‐Catalyzed Asymmetric Reduction of Ketone

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