36140-84-8Relevant articles and documents
Iodonium salts as efficient iodine(iii)-based noncovalent organocatalysts for Knorr-type reactions
Yunusova, Sevilya N.,Novikov, Alexander S.,Soldatova, Natalia S.,Vovk, Mikhail A.,Bolotin, Dmitrii S.
, p. 4574 - 4583 (2021/02/03)
Hypervalent iodine(iii)-derivatives display higher catalytic activity than other aliphatic and aromatic iodine(i)- or bromine(i)-containing substrates for a Knorr-type reaction of N-acetyl hydrazides with acetyl acetone to give N-acyl pyrazoles. The highe
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.
Resolution of secondary alcohols using 2-acyl-3-phenyl-l-menthopyrazoles as enantioselective acylating agents
Kashima, Choji,Mizuhara, Saori,Miwa, Yohei,Yokoyama, Yukihiro
, p. 1713 - 1719 (2007/10/03)
The chelation of AlCl3 with N-acylpyrazoles leads to structural fixation of the acyl moiety and an acceleration in the rate of acylation of secondary alcohols. The chiral environment of the fixed acyl moiety of 2-acyl-3-phenyl-l-menthopyrazole 2 causes diastereofacial selectivity in the reaction with secondary alcohols, and thus 2 behaves as an enantioselective acylating agent. By the use of 2.4 molar equivalents of racemic 1-phenylethanol 3a, 2-acetyl-3-phenyl-l-menthopyrazole 2a afforded (S)-1-phenylethyl acetate (S)-4aa enantioselectively and unreacted 3a was recovered with (R)-configuration. Furthermore, the inverse configurational preferences were observed to give (R)-4aa and (S)-3a by the addition of strongly basic amines, which sometimes behaved as catalysts for enolate formation from 2 and AlCl3. These dramatic changes in stereoselective preference should be useful properties of 2-acyl-3-phenyl-l-menthopyrazole 2 as an enantioselective acylating agent.
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.
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
