- Enantio- and Site-Selective α-Fluorination of N-Acyl 3,5-Dimethylpyrazoles Catalyzed by Chiral π–CuII Complexes
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Catalytic enantioselective α-fluorination reactions of carbonyl compounds are among the most powerful and efficient synthetic methods for constructing optically active α-fluorinated carbonyl compounds. Nevertheless, α-fluorination of α-nonbranched carboxylic acid derivatives is still a big challenge because of relatively high pKa values of their α-hydrogen atoms and difficulty of subsequent synthetic transformation without epimerization. Herein we show that chiral copper(II) complexes of 3-(2-naphthyl)-l-alanine-derived amides are highly effective catalysts for the enantio- and site-selective α-fluorination of N-(α-arylacetyl) and N-(α-alkylacetyl) 3,5-dimethylpyrazoles. The substrate scope of the transformation is very broad (25 examples including a quaternary α-fluorinated α-amino acid derivative). α-Fluorinated products were converted into the corresponding esters, secondary amides, tertiary amides, ketones, and alcohols with almost no epimerization in high yield.
- Ishihara, Kazuaki,Nishimura, Kazuki,Yamakawa, Katsuya
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supporting information
p. 17641 - 17647
(2020/08/14)
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- Direct Catalytic Chemoselective α-Amination of Acylpyrazoles: A Concise Route to Unnatural α-Amino Acid Derivatives
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A direct copper-catalyzed highly chemoselective α-amination is described. Acylpyrazole proved to be a highly efficient enolate precursor of a carboxylic acid oxidation state substrate, while preactivation by a stoichiometric amount of strong base has been used in catalytic α-aminations. The simultaneous activation of both coupling partners, enolization and metal nitrenoid formation, was crucial for obtaining the product, and wide functional group compatibility highlighted the mildness of the present catalysis. The bidentate coordination mode was amenable to highly chemoselective activation over ketone and much more acidic nitroalkyl functionality. Deuterium exchange experiments clearly demonstrated that exclusive enolization of acylpyrazole was achieved without the formation of a nitronate. The present catalysis was applied to late-stage α-amination, allowing for concise access to highly versatile α-amino acid derivatives. The product could be transformed into variety of useful building blocks.
- Tokumasu, Keisuke,Yazaki, Ryo,Ohshima, Takashi
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supporting information
p. 2664 - 2669
(2016/03/12)
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- Copper-catalyzed C–N cross-coupling of arylboronic acids with N-acylpyrazoles
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A copper-catalyzed C–N bond forming reaction of arylboronic acids and N-acylpyrazoles was developed. This procedure used N-acetyl protected pyrazoles as starting material instead of free pyrazoles (NH). The reaction worked under neutral conditions and did not require any base or ligand. The reaction showed good functional group tolerance.
- Zhang, Jin,Jia, Run-Ping,Wang, Dong-Hui
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supporting information
p. 3604 - 3607
(2016/07/21)
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- Preparation of β-substituted γ-keto esters by the grignard reaction on N-acylpyrazoles
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Various γ-keto esters were prepared by either the alcoholysis of N-(4-oxoalkanoyl)pyrazoles or the Grignard replacement of pyrazole moiety of 4-(N-pyrazolyl)-4-oxoalkanoic esters. By using 3-phenyl-ι-menthopyrazole as a chiral auxiliary, β-substituted γ-keto esters were enantioselectively obtained.
- Kashima, Choji,Shirahata, Yoshie,Tsukamoto, Yoshihiro
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p. 309 - 317
(2007/10/03)
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- Ring-ring tautomerism in 1,3-alkanoylhydrazonoximes of acetylacetone
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The coexistence in solution of tautomeric isoxazoline and pyrazoline forms of 1,3-alkanoylhydrazonoxime of acetylacetone has been detected and investigated by 1H and 13C NMR spectroscopic methods. The compounds indicated eliminate hydroxylamine under the action of acid catalysts, forming 1-acyl-3,5-dimethylpyrazoles.
- Ershov,Dobrodumov
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p. 722 - 727
(2007/10/03)
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- Diastereoselective α-alkylation of 2-acyl-3-phenyl-l-menthopyrazoles
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N-Acylpyrazoles were α-alkylated in good yields by the treatment with alkyl halides after metalation with LDA or LiHMDS. In the case of chiral N-acylpyrazoles, e.g., 2-acyl-3-phenyl-l-menthopyrazoles (4), the α-alkylation was highly diastereoselective. The subsequent α-alkylation products could be converted into esters in good yield in the presence of BF3·OEt2 without the loss of the optical purity.
- Kashima,Fukuchi,Hosomi
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p. 7821 - 7824
(2007/10/02)
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- The preparation of N-acetylpyrazoles and their behavior toward alcohols
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According to four different methods, various types of n-acylpyrazoles were prepared from the corresponding pyrazoles and carboxylic acids or their acid chlorides. Although A-acylpyrazoles were inert to alcohols under neutral or weakly basic conditions, th
- Kashima,Harada,Kita,Fukuchi,Hosomi
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