The Preparation of<i>N</i>-Acylpyrazoles and Their Behavior Toward Alcohols

Kashima, Choji; Harada, Hajime; Kita, I.; Fukuchi, Iwao; Hosomi, Akíra

doi:10.1055/s-1994-25406

Cited by 52 publications

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“…Previously N-acylation of trans-1 was studied to give Nacyl-3-phenyl-l-menthopyrazoles, isomers of which were easily purified by chromatographic separation [1]. Moreover, N-acyl-3-phenyl-l-menthopyrazoles were easily deacylated into trans-1 by the action of nucleophiles such as alcohols [18] and amines [19]. On the basis of these facts, the resolution of the isomeric mixture of cis-2 and trans-2 was undertaken by means of the acylation, chromatographic separation and the subsequent deacylation.…”

Section: Resultsmentioning

confidence: 99%

New optically active pyrazoles: Syntheses and the structural characterization of menthopyrazole analogues

Kashima¹,

Miwa²,

Shibata³

et al. 2002

Journal of Heterocyclic Chem

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New chiral pyrazoles, (4R, 7R)-4-methyl-7-isopropyl-3-phenyl-(3-phenyli s omenthopyrazole; c i s -1) , (4R,7S)-4-methyl-7-isopropyl-(l-menthopyrazole; trans-2), (4R,7R)-4-isopropyl-7-methyl-(isocarvomenthopyrazole, c i s-3) and (4R, 7S) -4 -i s o p r o p y l -7 -m e t h y l -4 , 5 , 6 , 7 -t e t r a h y d r o -1H-indazole (carvomenthopyrazole, trans-3) were prepared. The diastereomeric pairs of these 1-3 were structurally characterized by NMR spectroscopy. The subtle differences of structures of 1-3 should induce the useful effects for a chiral auxiliary or a chiral catalyst. , 7 -t e t r a h y d r o -1H-indazole (3-phenyl-l -m e n t h o p y r azole; trans-1) as a chiral auxiliary [1]. This auxiliary is easily prepared from commercially available l-menthone in good yield with high optical purity, and has unique structure and properties relative to the conventional chiral auxiliaries [2]. The most important characteristics of this auxiliary are that the substrate terminates to nitrogen atom of heteroaromatic pyrazole ring and that the 3-phenyl ring of trans-1 is close to the (4R)-methyl group. Subsequently, the steric repulsion is relaxed by rotation of the phenyl ring, and the substrate is located in the chiral environment. This structural feature causes the diastereofacial attack on the substrate moiety in the reactions with alkyl halides [3], diphenyldisulfide [4], acyl chloride [5], aldehydes [6], and C=N compounds [7]. Moreover, the asymmetric additions of Grignard reagents [8], dienes [9] and 1,3-dipolar compounds [10] on 2-(α , βu n s a t u r a t e d ) a c y l -3 -p h e n y l-l -m e nthopyrazoles have been reported. Otherwise, the extensive use of these optically active pyrazoles was studied as the chiral catalyst for the asymmetric borane reduction of ketones [11,12] and the asymmetric dialkylzinc addition on aldehydes [13].

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Section: Resultsmentioning

confidence: 99%

New optically active pyrazoles: Syntheses and the structural characterization of menthopyrazole analogues

Kashima¹,

Miwa²,

Shibata³

et al. 2002

Journal of Heterocyclic Chem

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“…Found: C,76.11;H,8.71;N,9. ,9.97;N,12.6. Found: C,69.95;H,9.79;N,12. 29.0 (CH), 31.6 (CH), 36.9 (CH), 50.7 (CH 2 ), 61.9 (CH 2 ), 121.9 (C), 136.3 (CH), 141.2 (C).…”

Section: -[ -O X O --( 1 -N a P H T H Y L ) E T H Y L ] -3 -P H E N Ymentioning

confidence: 99%

“…Otherwise, N -acylheteroaromatics such as N-acylimidazoles are utilized as the activated acyl moiety in a wide varieties of organic syntheses [11]. As an analogue of these N-acylheteroaromatics, N-acylpyrazoles are easily converted into acyl derivatives by the action of nucleophiles such as alcohols [12], amines [13], Grignard reagents [14], or organozinc compounds [15] under basic or acidic conditions. Many reports of chiral amino alcohols relating to enantioselective synthesis have appeared in the literature.…”

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confidence: 99%

Asymmetric Reaction of Diethylzinc with Aldehydes Catalyzed by l‐Menthopyrazole Derivatives.

et al. 2003

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N-Hydroxyalkyl-l-menthopyrazoles acted as a chiral catalyst for the diethylzinc (1) addition to aromatic aldehydes, and 1-aryl-1-propanols were afforded enantioselectively. These reactions were carried out optimally in toluene at 40 °C in the presence of 30 mol% of (2'S)-2-(2-phenyl-2-hydroxyethyl)-3-phenyl-l-menthopyrazole ((S)-16d) to afford optically active 1-aryl-1-propanols up to 70% ee (S).J. Heterocyclic Chem., 39, 917(2002).Recently we have developed the preparation and the utilities of 3-phenyl-l-menthopyrazole as a new chiral auxiliary [1], which has a unique structure and properties relative to the conventional chiral auxiliaries [2]. The most important characteristics of this auxiliary are that the substrate terminates at a nitrogen atom of the heteroaromatic pyrazole ring, and that the substrate is surrounded by the chiral environment. These structural features cause the diastereofacial attack on the substrate moiety in the reactions with alkyl halides Many reports of chiral amino alcohols relating to enantioselective synthesis have appeared in the literature. The chiral amino alcohols behave as a ligand for a metal atom to form a complex, which takes the role of an optically active Lewis acid. Since l -menthopyrazole derivatives exhibit both the characteristic of Lewis basicity and asymmetric structure, the introduction of a hydroxyl group was expected to exploit the utilities of l-menthopyrazoles as a ligand for an optically active Lewis acid. On this strategy, the utility of l -menthopyrazole derivatives having an hydroxyalkyl group was investigated as an optically active catalyst for the borane reduction of ketones [16]. As a part of these investigations been hoped to extend the catalytic use of pyrazole derivatives in synthetic reactions especially in asymmetric reactions.Recently, Soai and his co-workers focused their attention on the addition reaction of dialkylzinc toward aldehydes in the presence of chiral amino alcohols, and elucidated their enantioselective reaction mechanism, catalyzed by an optically active Lewis acid [17]. Since then, some papers using various amino alcohols followed to give similar enantioselective addition of dialkylzinc toward aldehydes [18]. With the background, we wish to report the reaction of diethylzinc with aldehydes catalyzed by l -m e nthopyrazoles having the hydroxylalkyl group. Results and DiscussionN-(1-Hydroxyalkyl)pyrazoles were previously reported to be prepared by the action of aldehydes toward N-unsubstituted pyrazoles [16a]. From these facts, the Lewis acid complex of N-(1-hydroxyalkyl)pyrazoles with dialkylzinc should be formed in situ by aldehydes with pyrazoles. Moreover, this complex was expected to act as a self-catalyst in the addition reaction of dialkylzinc to aldehydes. Actually 1-(4-methylphenyl)-1-propanol (3 a) was obtained by the action of diethylzinc (1) toward 4-methylbenzaldehyde (2a) in the presence of 3,5-dimethylpyrazole (4). This catalytic effect was observed with less than 30 mol% of 4. These results indicated the catalytic effec...

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“…1 Moreover and according to some authors, this condensation leads to the formation of the undesired isomer as a major component. [2][3][4] Thereafter, direct substitution of N-nonsubstituted pyrazoles under previous reported conditions [5][6][7][8] such as K 2 CO 3 /DMF, K 2 CO 3 /DMSO, KOH/Bu 4 NBr, KOtBu and NaH/THF provide another powerful method for synthesis of N-arylpyrazoles. However, the reaction generally gives also a mixture of two regioisomers since pyrazole is an ambident nucleophile.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of some 1-aryl-3,5-disubstituted-pyrazoles by N-arylation of 3,5-disubstituted-pyrazoles with 4-fluoro and 2-fluoronitrobenzene under microwave irradiation and classical heating

Bouabdallah¹,

Touzani²,

Zidane³

et al. 2006

Arkivoc

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N-Arylation of 3,5-disubstituted-pyrazoles with 4-fluoro and 2-fluoronitrobenzene under microwave irradiation conditions with and without solvent compared to the classical heating afforded, N-arylation regioisomers in yields depending on the method used. The structures of compounds : 1-aryl-3,5-disubstituted-pyrazoles were confirmed by IR, 1 H-NMR, 13 C-NMR spectroscopy, elemental analysis and mass spectrometry.

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The Preparation ofN-Acylpyrazoles and Their Behavior Toward Alcohols

Cited by 52 publications

References 0 publications

New optically active pyrazoles: Syntheses and the structural characterization of menthopyrazole analogues

New optically active pyrazoles: Syntheses and the structural characterization of menthopyrazole analogues

Asymmetric Reaction of Diethylzinc with Aldehydes Catalyzed by l‐Menthopyrazole Derivatives.

Synthesis of some 1-aryl-3,5-disubstituted-pyrazoles by N-arylation of 3,5-disubstituted-pyrazoles with 4-fluoro and 2-fluoronitrobenzene under microwave irradiation and classical heating

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