Solvent-Free Benzoin and Stetter Reactions with a Small Amount of NHC Catalyst in the Liquid or Semisolid State

Ema, Tadashi; Nanjo, Yoshiko; Shiratori, Sho; Terao, Yuta; Kimura, Ryo

doi:10.1021/acs.orglett.6b03115

Cited by 38 publications

(35 citation statements)

References 69 publications

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“…Shortly after, the same reaction was also reported by Ema et al. with merely 0.5–1.0 mol% of NHC precatalyst 143 under solvent‐free conditions, however, the reported three coupling products 144 were obtained with modest enantioselectivities …”

Section: Cross‐benzoin Reactionssupporting

confidence: 77%

Recent Advances in Catalytic Asymmetric Synthesis of Tertiary Alcohols via Nucleophilic Addition to Ketones

2018

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Chiral tertiary alcohols are an important class of organic compounds which have found wide applications in both academia and industry. Therefore, various synthetic strategies towards these compounds have already been developed. Among them, the catalytic asymmetric addition of carbon nucleophiles to ketones is the most desirable route owing to its straightforwardness as well as its economic, efficient and versatile advantages. This review summarizes and discusses the recent achievements in this field classified according to the reaction types. Special attention is paid to the mechanisms, advantages and limitations of each reaction. In addition, the applications of these catalytic processes in the synthesis of related natural products, pharmaceuticals or their analogues are briefly discussed as well.

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Section: Cross‐benzoin Reactionssupporting

confidence: 77%

Recent Advances in Catalytic Asymmetric Synthesis of Tertiary Alcohols via Nucleophilic Addition to Ketones

2018

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“…20–22 This type of reaction was first reported by Nair, using imidazolium precatalyst 3 , which yielded the anti product as the major diastereomer. 19 Enantioselective variations, using chiral triazolium precatalysts, were reported by the Rovis and Liu groups, respectively, in 2013 and 2012. 20,21 Liu's precatalyst, 4 , favors the anti isomer, while Rovis' precatalyst 5 favors the syn isomer.…”

Section: Resultsmentioning

confidence: 99%

Experimental and Computational Gas Phase Acidities of Conjugate Acids of Triazolylidene Carbenes: Rationalizing Subtle Electronic Effects

et al. 2017

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In recent years, triazolylidene carbenes have come to the forefront as important organocatalysts for a wide range of reactions. The fundamental properties of these species, however, remain largely unknown. Herein, the gas phase acidities have been measured and calculated for a series of triazolium cations (the conjugate acids of the triazolylidene carbenes) that have not been heretofore examined in vacuo. The results are discussed in the context of these species as catalysts. We find correlations between the gas phase acidity and selectivity in two Umpolung reactions catalyzed by these species; such correlations are the first of their kind. We are able to use these linear correlations to improve reaction enantioselectivity. These results establish the possibility of using these thermochemical properties to predict reactivity in related transformations.

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“…In recent years, N-heterocyclic carbenes (NHCs) catalysis proved to be one kind of the most reliable organocatalyst and versatile platform in organocatalysis, and plenty of complex carbo-and heterocycles have been constructed via various umpolung or non-umpolung strategies [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Many kinds of chiral NHCs have been developed to catalyze stereochemical reactions, in which one of the most popular and effective structural scaffolds proved to be the aminoindanol skeleton.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of (−)-Verbenone-Derived Triazolium Salts and Their Application in Enantioselective Intramolecular Stetter Reaction

Rafiński

Krzemiński

2019

Catalysts

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Two novel chiral verbenone-derived triazolium salts have been synthesized from readily available (−)-verbenone and found to be efficient for the enantioselective intramolecular Stetter reaction. The approach, based on the intramolecular annulation between acyl anion equivalents and Michael acceptors, benefits from broad substrate scope, high chemical and stereochemical efficiency, and operational simplicity. Mono-, and disubstituded chromanone derivatives have been obtained in excellent yields and in a highly stereochemical manner.Catalysts 2019, 9, 117 2 of 12 ketooxime 4 in 87% yield by treatment with isoamyl nitrite. Due to the fact, that verbenone is not commercially available in an enantiomerically pure form, attempts of enantiomeric enrichment through crystallization at the ketoxime stage failed. Hence, we decided to reduce the carbonyl group by treatment of 4 with sodium borohydride in ethanol. Gratifyingly, crystallization of the crude 5 gave the enantiomerically pure hydroxyoxime 5 in 99% ee. Stereoselective reduction of 5 with lithium aluminium hydride afforded the amino alcohol 6 in 63% yield, which was immediately used to the next step without further purification. The lactam 8 was prepared by previously reported two-step procedure involving the formation of chloroamide 7, followed by the cyclization reaction with the use of potassium tert-butoxide. Finally, a one-pot procedure was used for the three-step conversion into triazolium salts 1A-B. The NHC precatalyst 1B could be easily and cleanly isolated as a tetraphenyl borate salt. For the salt 1A, preparation does not require chromatographic purification. Evaporation of the solvent followed by washing with diethyl ether provided a pure product that was air-and water-stable solid.

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Solvent-Free Benzoin and Stetter Reactions with a Small Amount of NHC Catalyst in the Liquid or Semisolid State

Cited by 38 publications

References 69 publications

Recent Advances in Catalytic Asymmetric Synthesis of Tertiary Alcohols via Nucleophilic Addition to Ketones

Recent Advances in Catalytic Asymmetric Synthesis of Tertiary Alcohols via Nucleophilic Addition to Ketones

Experimental and Computational Gas Phase Acidities of Conjugate Acids of Triazolylidene Carbenes: Rationalizing Subtle Electronic Effects

Synthesis of (−)-Verbenone-Derived Triazolium Salts and Their Application in Enantioselective Intramolecular Stetter Reaction

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