Synthesis of some 4-hydroxy-2-pyrrolin-5-one derivatives via acyloin rearrangement

Gelin, Suzanne; Gelin, Rene

doi:10.1021/jo01319a032

Cited by 17 publications

(4 citation statements)

References 3 publications

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“…However, we did observe trace aldehyde in the crude 1 H NMR of the reaction mixture. The presence of an aldehyde could be the result of our proposed retro-benzoin reaction (Figure ) or the product of a base-mediated acyloin rearrangement . Intrigued by the former possibility, we wanted to validate the possibility that our proposed dialdehyde intermediate ( 9 ) could indeed be cyclized to macrolide 6 .…”

Section: Resultsmentioning

confidence: 98%

Development of a Bio-Inspired Acyl-Anion Equivalent Macrocyclization and Synthesis of a trans-Resorcylide Precursor

Mennen

Miller

2007

J. Org. Chem.

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Studies on the macrocyclization of alpha,omega-dialdehydes have revealed a strong dependence on ring size with respect to the ultimate efficiency of the reaction. Strong catalyst dependence was observed, as thiazolium salts led to no detectable product formation, whereas electron-deficient triazolium salts served as precatalysts for the cyclization. Surprisingly, the N-pentafluorophenyl triazolium variant led to cyclization at room temperature within a short 90-min reaction time. These findings were applied to a range of substrates, including the synthesis of a key intermediate in a rapid synthesis of trans-resorcylide.

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Section: Resultsmentioning

confidence: 98%

Development of a Bio-Inspired Acyl-Anion Equivalent Macrocyclization and Synthesis of a trans-Resorcylide Precursor

Mennen

Miller

2007

J. Org. Chem.

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“…4-Ethoxycarbonyl-1,5-dimethyl-3-phenylacetylpyrazole (9b) was obtained by recrystallization of residual solid mixture 9a/9b, 20:80, from ethyl acetate-hexane, 30:70 3.7 g (65%); mp 71 "C. Anal. 9 30.3 C'-1, 131.7; C'-2,6, 128.4;' C H~: 128.8;6,129.4;129.3;6,129.4;5,127.8;128.6' Ketenimines are an important class of organic compounds, which are apt to undergo a variety of photochemical and thermal cycloadditions.2a Several entries into this cumulenic system have been described,2a but the overwhelming number of ketenimines described hitherto are substituted with one or more aromatic substituents. 9 30.3 C'-1, 131.7; C'-2,6, 128.4;' C H~: 128.8;6,129.4;129.3;6,129.4;5,127.8;128.6' Ketenimines are an important class of organic compounds, which are apt to undergo a variety of photochemical and thermal cycloadditions.2a Several entries into this cumulenic system have been described,2a but the overwhelming number of ketenimines described hitherto are substituted with one or more aromatic substituents.…”

Section: -Acetyl-1 -Benzyl-4-ethoxycarbonyl-3-methylpyrazole (12a)mentioning

confidence: 99%

“…5, 128.6; 127.2 132.6;6, 129.7;5,128.5; 127.0b 195.5 CH2: 49.6; Ph: C'54.0; Ph: C'-1, 135.4; C'-2,6, 127.8;" c'-3,5, 128.3;" C'-4, 128.0b " s h These values might be interchanged.…”

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confidence: 99%

Synthesis of the N-alkyl isomers of 4-ethoxycarbonyl-or-acetyl-3(5)-alkyl-or-aryl-5(3)-acylpyrazoles from 3(2H)-furanones. Structure determination

Gelin¹,

Gelin²,

Hartmann³

1978

J. Org. Chem.

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Synthesis of isomeric N-alkyl-3,4,5-trisubstituted pyrazoles are described from reaction of 3(2H)-furanones with alkylhydrazines or alternatively by alkylation of corresponding N-unsubstituted pyrazoles. Their structures are unambiguously established by 'H and 13C NMR studies. By comparison of the data of the N-alkylpyrazoles with those of the N-unsubstituted pyrazoles, the 5-methyl and 5-phenyl structures were found as the predominant form for these pyrazoles.Recently, we have reported that the 3(2H) -furanones are interesting substrates which undergo ring opening by nucleophilic reagents, leading to new cyclic c o m p o~n d s . l -~ Our studies concerning the reaction of hydrazine hydrate with 3(2H)-furanones 1-4 have led to a useful procedure to obtain Trialkylketenimines were prepared by reaction of a-cyano enamines w i t h methylmagnesium iodide in ethereal solution. Condensation of trialkylketenimines w i t h p r i m a r y amines afforded the corresponding amidines.

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“…Many a-hydroxy ketones have the capacity for conversion to an isomeric a-ketol. Catalysis by a base, [1] inorganic salt, [2] Br˘nsted acid, [3] or Lewis acid [4] is generally required. Two mechanistic pathways are possible depending on structural features.…”

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confidence: 99%

Fluoride Ion‐Promoted α‐Ketol Rearrangement during Unmasking of Silyl‐Protected Medium‐Ring Dihydroxy Ketones

2004

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Dedicated to Joe P. Richmond on the occasion of his 60 th birthday.Abstract: A new strategy for implementing a-ketol rearrangements under mild conditions is presented. The reactants are mono-and disilylated stereoisomers of a,a'-and a,b-dihydroxycycloheptanones and -cyclooctanones. Compounds of this class experience ready deprotection upon treatment with tetrabutylammonium fluoride. In certain examples, this process is accompanied by structural isomerization. Since the product diols are stable to the reaction conditions, these chemical changes have been attributed to kinetically controlled events following transient alkoxide generation resulting from cleavage of the O À Si bond proximal to the carbonyl group. The experimental findings are evaluated against a backdrop of calculated (MM3) steric energies of the siliconfree products and their response to equilibration under strongly basic conditions.Keywords: desilylation; fluoride ion; a-ketols; medium-sized rings; MM3 calculations; rearrangement Many a-hydroxy ketones have the capacity for conversion to an isomeric a-ketol. Catalysis by a base, [1] inorganic salt, [2] Br˘nsted acid, [3] or Lewis acid [4] is generally required. Two mechanistic pathways are possible depending on structural features. When the hydroxy group forms part of a tertiary carbinol, a 1,2-alkyl or aryl shift as depicted for operates.[5] Secondary a-keto carbinols can also isomerize via an enediol intermediate typified by 3.[6 ± 10] In both cases, the rearrangement is reversible, such that thermodynamic control is operative and the more stable isomer results. If the enthalpically advantaged member of the pair is already in hand, a chemical transformation will not likely operate under the predescribed conditions provided that the energy difference is sufficiently great.Extensive attention has been accorded to acyclic, cyclic, bridged, and steroidal a-ketols, such that ring-size effects and the impressively high levels of attainable selective bond migration are well appreciated.[5] In contrast, heteroatomic substituent effects in the vicinity of the carbonyl group appear not to have been given prior attention. The recent availability of monosilylated medium-ring a,a'-dihydroxycycloalkanones in our laboratory [11] has prompted a probe of the manner in which the individual cis-and trans-isomers react when desilylated. The generation of tautomeric a-ketol products has been found to occur under conditions sufficiently mild [1d,12] that the resulting dihydroxy ketones are not concurrently equilibrated. These observations constitute a previously unrecognized means for implementing a-ketol rearrangements.We first addressed the direct desilylation of 4 and its diprotected congener 5 with tetra-n-butylammonium fluoride (TBAF) in tetrahydrofuran at room temperature for 30 min. In the event, the dihydroxy ketones 6 and 7 were formed in an identical ratio of 2 : 1 in these examples. The structural assignments to the products are based upon direct spectral comparisons with authentic samples. The trans relat...

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Synthesis of some 4-hydroxy-2-pyrrolin-5-one derivatives via acyloin rearrangement

Cited by 17 publications

References 3 publications

Development of a Bio-Inspired Acyl-Anion Equivalent Macrocyclization and Synthesis of a trans-Resorcylide Precursor

Development of a Bio-Inspired Acyl-Anion Equivalent Macrocyclization and Synthesis of a trans-Resorcylide Precursor

Synthesis of the N-alkyl isomers of 4-ethoxycarbonyl-or-acetyl-3(5)-alkyl-or-aryl-5(3)-acylpyrazoles from 3(2H)-furanones. Structure determination

Fluoride Ion‐Promoted α‐Ketol Rearrangement during Unmasking of Silyl‐Protected Medium‐Ring Dihydroxy Ketones

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