Structure–enantioselectivity correlation in NHC–Au(I) catalysis for 1,6-enynecyclizations

Gung, Benjamin W.; Holmes, Michael; Jones, Caleb A. H.; Ma, Ruoyu; Barnes, Charles L.

doi:10.1016/j.tetlet.2016.07.046

Cited by 18 publications

(14 citation statements)

References 19 publications

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“…Considering the activity of gold(I) chloride complexes in catalysis, in particular enantioselective processes, they have to be activated prior to use by the abstraction of the halide ion with silver salts bearing weakly coordinating anions, such as tetrafluoroborate or hexafluorophosphate [68]. Indeed, Gung proved that gold(I) complexes 14 could form stable ionic complexes with the metal center additionally protected by a nitrile ligand [66].…”

Section: Cyclic C 2 -Symmetric Gold(i) Complexesmentioning

confidence: 99%

“…The conformation of compound 20 also revealed that para-methoxyphenyl substituents are located in a parallel arrangement relative to the benzimidazolium skeleton. The synthetic route leading to C 2 -symmetric complexes 13 decorated with biphenyl subunits was developed by Gung (Scheme 2) [65][66][67]. In contrast to Kündig's methodology, the authors used less expensive sources of the precarbenic unit, e.g.…”

Section: Cyclic C 2 -Symmetric Gold(i) Complexesmentioning

confidence: 99%

“…Application of PtCl 2 /(R)-BINEPINE (154) has been only reported [107] leading to cyclopentane derivative 153 with comparable enantioselectivity and yield. Catalysts 2019, 9, Structurally similar cyclopentane derivatives 153 bearing a malonate moiety were also investigated by Tomioka [62,106], Gung [66], and recently, Zhang [90] (Scheme 27). Tomioka's catalysts 7 resulted in cyclopentane derivative 153 with moderate enantioselectivity, whereas Gung's ionic catalyst 14 appeared to be slightly better in terms of stereoselectivity.…”

Section: Intramolecular Reactions Alkylidene Cyclopentane Derivativesmentioning

confidence: 99%

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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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Section: Cyclic C 2 -Symmetric Gold(i) Complexesmentioning

confidence: 99%

Section: Cyclic C 2 -Symmetric Gold(i) Complexesmentioning

confidence: 99%

Section: Intramolecular Reactions Alkylidene Cyclopentane Derivativesmentioning

confidence: 99%

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

Michalak

Kośnik

2019

Catalysts

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“…46 Hence, reaction of either (S)-(-)-α-methylbenzylamine or (S)-(-)-1-(1-naphthyl)ethylamine with glyoxal and paraformaldehyde in the presence of either HCl or HBF 4 at 40 °C in toluene overnight afforded the desired salts. We assume that, based upon literature precedent, 32 the synthesis of the imidazolium salts 6, 7 and 8 and subsequent conversion into 11 and 12 proceeds without racemization, an outcome which is in keeping with subsequent X-ray analysis of 11 and 12.…”

Section: Synthesis Of Chiral Gold Complexesmentioning

confidence: 99%

“…12,13 Despite the ever burgeoning literature concerning gold-catalysed reactions, the majority of structurally defined chiral gold complexes are restricted to those bearing chiral phosphane ligands. [14][15][16][17][18][19] Given the fact the use of gold-NHC complexes [20][21][22][23][24][25][26] is now de rigour in synthesis, it is somewhat surprising that reports of structurally characterised, chiral, Au(I)-NHC [27][28][29][30][31][32][33][34][35][36] and Au(I)-ADC/NAC 37 complexes are still comparatively scarce. Likewise, the synthesis and characterisation and catalytic activity of cyclometallated gold(III) complexes is relatively unexplored, with only a handful of examples being cited in the literature.…”

Section: Introductionmentioning

confidence: 99%

Some insights into the gold-catalysed A 3 -coupling reaction

Price

Brisdon

Randall

et al. 2017

Journal of Organometallic Chemistry

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Abstract.A series of cyclometallated and functionalised NHC gold(I) and gold(III) complexes, many of which feature chiral ligands, and their application to A 3 -coupling reactions is presented. Gold(III) complexes were found to be particularly effective catalysts for the coupling in a range of solvents, however no asymmetric induction was obtained when using chiral gold complexes and the rate of product formation was found to be similar even when using different ligand systems. In-situ NMR analysis of these reactions indicates that decomposition of the catalyst occurs during the course of the reaction while TEM studies revealed the presence of gold nanoparticles in crude reaction mixtures. Taken together these data suggest that the gold nanoparticales, rather than the intact gold complexes, could be the catalytically active species, and if so this may have significant implications for other gold-catalysed systems.Dedicated to Dr. Mark Whiteley (an outstanding colleague) on his retirement from the School of Chemistry, University of Manchester.

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