Preparation of chiral 1,2,4-triazolium salts as new NHC precatalysts

Strand, Ragnhild B.; Solvang, Tina; Sperger, Christian A.; Fiksdahl, Anne

doi:10.1016/j.tetasy.2012.06.002

Cited by 9 publications

(6 citation statements)

References 34 publications

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“…Furthermore, the products are important key intermediates for the synthesis of numerous heterocycles . As shown in Scheme a, the products can be easily transformed to chiral 1,2,4-triazolium salt N-heterocyclic carbene (NHC) precursors 4 , which can be used for enantioselective catalysis …”

supporting

confidence: 71%

“…28 As shown in Scheme 4a, the products can be easily transformed to chiral 1,2,4-triazolium salt N-heterocyclic carbene (NHC) precursors 4, which can be used for enantioselective catalysis. 29 The proposed mechanism of this transformation, which is in accordance with diverse performed mechanistic experiments (see the SI for further information) and literature reports on the direct sensitization of mesoionic sydnones (λ < 300 nm) 18 , is depicted in Scheme 4b. The [Ru II ] photocatalyst is excited by visible light to its triplet excited state (E T = 48.4 kcal/ mol).…”

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confidence: 99%

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Accelerated Discovery in Photocatalysis by a Combined Screening Approach Involving MS Tags

et al. 2019

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Herein we report on the development of an MS tag screening strategy that accelerates the discovery of photocatalytic reactions. By efficiently combining mechanism-and reaction-based screening dimensions, the respective advantages of each strategy were retained, whereas the drawbacks inherent to each screening approach could be eliminated. Applying this approach led to the discovery of a mild photosensitized decarboxylative hydrazide synthesis from mesoionic sydnones and carboxylic acids as starting materials.

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confidence: 71%

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confidence: 99%

Accelerated Discovery in Photocatalysis by a Combined Screening Approach Involving MS Tags

et al. 2019

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“…Traditionally, 1-aryl-substituted 1,2,4-triazolium salts are prepared in three steps via a condensation reaction between an oxadiazolium intermediate derived from an aryl hydrazine and a primary amine (Scheme a). − There are several disadvantages of this synthetic route: First, the oxadiazolium intermediates are not only highly water-sensitive and decompose within minutes upon exposure to air but their formation also requires perchloric acid, thus raising safety concerns regarding the scaling up of the procedure. Second, many aryl hydrazines are either not readily available or very expensive.…”

Section: Introductionmentioning

confidence: 99%

Catalytic Preparation of 1-Aryl-Substituted 1,2,4-Triazolium Salts

et al. 2019

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1,4-Diaryl- and 1-aryl-4-alkyl-substituted 1,2,4-triazolium salts are convenient air-stable precursors to carbenes used both as organocatalysts or as ligands for transition metal complexes. Traditionally, they are prepared via a multistep synthetic pathway with the low-yielding formation of the triazolium ring occurring in the last step. We have developed an alternative two-step synthesis involving the conversion of a primary amine or aniline derivative to the corresponding 4-substituted triazole followed by a copper-catalyzed arylation with diaryliodonium salts. This transition metal-catalyzed arylation can be carried out under mild conditions in acetonitrile and is tolerant toward both water and oxygen. Additionally, the high functional group tolerance of the protocol described here gives easy access to triazolium salts containing heterocyclic substituents or sulfides.

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“…Fiksdahl and co-workers reported a synthesis based on Lphenylalanine, which was converted into a benzylated amino alcohol 216 in a reduction/benzylation sequence, and (S)-α-methylbenzylamine (Scheme 40). 79 The formylation of phenylhydrazine (213) gave 214, which was cyclized in a mixture of Ac 2 O and HClO 4 to give oxadiazolium salt 215. Reaction of 215 with the amines 216 or 73a afforded NHC precursors 217.…”

Section: Scheme 39 the Synthesis Of Triazolium Salts Via Substitutionmentioning

confidence: 99%

“…Fiksdahl and co-workers showed a straightforward synthesis of a structurally simple salt from L-phenylalanine (281). 79 The respective amide 282 was subjected to the Leeper and Knight methodology. Unfortunately, the salt 283 was obtained with poor yield due to a problematic cyclization step (Scheme 52).…”

Section: Scheme 50 the Synthesis Of Tricyclic Nhc Precursormentioning

confidence: 99%

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

Czerwiński¹,

Michalak

2019

Synthesis

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N-Heterocyclic carbenes and their metal complexes have found applications in many organic transformations. Apart from the privileged C 2-symmetry present in modern enantioselective catalysis, ligands bearing C 1-symmetry have witnessed growing attention due to the better control of process stereoselectivity in many cases. The present review summarizes, for the first time, the seminal synthetic efforts for the preparation of N-heterocyclic carbene precursors exhibiting C 1-symmetry. The well-established methods will be discussed in the light of recent achievements, giving a direct opportunity for comparison of the existing methods, and simultaneously a chance to find the best synthetic pathway for the ideal chiral ligand.1 Introduction2 Five-Membered Rings2.1 Five-Membered Saturated (Imidazolinium) Ring2.1.1 Amino Alcohol Derivatives2.1.2 Amino Acid Derivatives2.1.3 Amine and Diamine Derivatives2.2 Five-Membered Unsaturated Ring2.2.1 Cyclization Strategy2.2.2 Functionalization of the Existing N-Imidazole Ring3 Triazolium Salts3.1 Substitution in Oxadiazolium Salts3.2 Lactam-Derived Triazolium NHC (The Leeper and Knight Methodology)3.3 Monoterpenoid-Derived NHC Triazolium Salts3.4 Modifications of the Existing Triazole Ring4 Thiazole-Derived Salts4.1 Cyclization of a Thiazolium Ring4.2 Modifications of the Existing Thiazole Ring5 Summary and Outlook

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Preparation of chiral 1,2,4-triazolium salts as new NHC precatalysts

Cited by 9 publications

References 34 publications

Accelerated Discovery in Photocatalysis by a Combined Screening Approach Involving MS Tags

Accelerated Discovery in Photocatalysis by a Combined Screening Approach Involving MS Tags

Catalytic Preparation of 1-Aryl-Substituted 1,2,4-Triazolium Salts

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

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