37612-61-6Relevant academic research and scientific papers
Enantio- and Site-Selective α-Fluorination of N-Acyl 3,5-Dimethylpyrazoles Catalyzed by Chiral π–CuII Complexes
Ishihara, Kazuaki,Nishimura, Kazuki,Yamakawa, Katsuya
supporting information, p. 17641 - 17647 (2020/08/14)
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.
Direct Catalytic Chemoselective α-Amination of Acylpyrazoles: A Concise Route to Unnatural α-Amino Acid Derivatives
Tokumasu, Keisuke,Yazaki, Ryo,Ohshima, Takashi
supporting information, p. 2664 - 2669 (2016/03/12)
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.
Copper-catalyzed C–N cross-coupling of arylboronic acids with N-acylpyrazoles
Zhang, Jin,Jia, Run-Ping,Wang, Dong-Hui
supporting information, p. 3604 - 3607 (2016/07/21)
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.
Preparation of β-substituted γ-keto esters by the grignard reaction on N-acylpyrazoles
Kashima, Choji,Shirahata, Yoshie,Tsukamoto, Yoshihiro
, p. 309 - 317 (2007/10/03)
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.
Ring-ring tautomerism in 1,3-alkanoylhydrazonoximes of acetylacetone
Ershov,Dobrodumov
, p. 722 - 727 (2007/10/03)
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.
Diastereoselective α-alkylation of 2-acyl-3-phenyl-l-menthopyrazoles
Kashima,Fukuchi,Hosomi
, p. 7821 - 7824 (2007/10/02)
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.
The preparation of N-acetylpyrazoles and their behavior toward alcohols
Kashima,Harada,Kita,Fukuchi,Hosomi
, p. 61 - 65 (2007/10/02)
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
