Carboxy(vinyl)ketene intermediates in the thermolysis of methylthio- and methoxy-substituted Meldrum’s acid derivatives

Bibas, Hervé; Kappe, C. Oliver; Wong, Ming Wah; Wentrup, Curt

doi:10.1039/a708585k

Cited by 12 publications

(4 citation statements)

References 31 publications

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“…Additional NOE correlations prove the Z configuration of 27-H and the 28-methoxy group, while no NOE could be detected for the methyl group C-29. [12] (Table 1). The relative configuration of C-8 and C-9 of the isochromanone residue was evident from the vicinal coupling J 8,9 ϭ 6.7 Hz [13] clearly observed for the 8-H signal after H/D exchange.…”

Section: Resultsmentioning

confidence: 99%

The Ajudazols A and B, Novel Isochromanones fromChondromyces crocatus (Myxobacteria): Isolation and Structure Elucidation

et al. 2002

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Section: Resultsmentioning

confidence: 99%

The Ajudazols A and B, Novel Isochromanones fromChondromyces crocatus (Myxobacteria): Isolation and Structure Elucidation

et al. 2002

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“…α-Oxoketenes 2 have been the focus of numerous theoretical and experimental studies . They have been observed by thermolysis of Meldrum's acid derivatives in boiling diphenyl ether (259 °C) or under flash vacuum pyrolysis condition (600 °C, 0.01 Torr). , In light of these studies, 2 has been suggested as a possible intermediate in reactions in which acyl Meldrum's acid adducts react with amines, alcohols, and imines, etc., although the alternative pathway through nucleophilic addition to intermediate 1 followed by elimination cannot be excluded. 5b, Almqvist et al suggested that formation of β-lactams is a [2 + 2] product of α-oxoketene 2 and a thiazoline. Subsequently, they also proposed that 2-pyridinone is formed through protonated ketene intermediate 3 when branched imines are subjected to the same reaction conditions as for the preparation of β-lactams .…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Evidence for an α-Oxoketene Pathway in the Formation of β-Ketoamides/Esters via Meldrum's Acid Adducts

Armstrong

Zhou

et al. 2004

J. Am. Chem. Soc.

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A practical, one-pot process for the preparation of beta-keto amides via a three-component reaction, including Meldrum's acid, an amine, and a carboxylic acid, has been developed. Key to development of an efficient, high-yielding process was an in-depth understanding of the mechanism of the multistep process. Kinetic studies were carried out via online IR monitoring and subsequent principal component analysis which provided a means of profiling the concentration of both the anionic and free acid forms of the Meldrum's adduct 6 in real time. These studies, both in the presence and absence of nucleophiles, strongly suggest that formation of beta-keto amides from acyl Meldrum's acids occurs via alpha-oxoketene species 2 and rule out other possible reaction pathways proposed in the literature, such as via protonated alpha-oxoketene intermediates 3 or nucleophilic addition-elimination pathways.

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“…89,90 Similar mechanisms also ensue when the 5-alkylidene derivative contains a methylthio-or alkoxy substituent at the methylene position. 91 Contrary to an earlier report, 51b alkoxy(methyl)methyleneketene 163 (R = Me, X = O) does not isomerize to (1-alkoxyvinyl)ketenes 166. 91 All of these intermediates have been fully characterised by matrix isolation, IR spectroscopy and the structures have been supported by theoretical calculations.…”

Section: Scheme 35mentioning

confidence: 61%

“…91 Contrary to an earlier report, 51b alkoxy(methyl)methyleneketene 163 (R = Me, X = O) does not isomerize to (1-alkoxyvinyl)ketenes 166. 91 All of these intermediates have been fully characterised by matrix isolation, IR spectroscopy and the structures have been supported by theoretical calculations. This detailed mechanistic work provides strong support for the more synthetically orientated studies, such as the formation of the thiophenone 167 (c.f.…”

Section: Scheme 35mentioning

confidence: 61%

Synthetic Applications of the Pyrolysis of Meldrum's Acid Derivatives

Gaber¹,

McNab²

2001

Synthesis

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The pyrolysis of Meldrum's acid (2,2-dimethyl-1,3-dioxane-4,6-dione) 1 derivatives in solution and in the gas-phase takes place by loss of acetone and carbon dioxide to provide ketene intermediates. In particular, methylene Meldrum's acid derivatives 7 often provide methyleneketenes 8, which act as substrates for internal hydrogen transfer leading to cyclisation reactions. The availability of versatile synthetic routes to 7 (in particular R = heteroatom) has led to the efficient preparation of a diverse range of cyclic compounds such as quinolinones, 3-hydroxythiophenes, naphthols, azepin-3(2H)-ones or pyrrolizin-3-ones initiated respectively by 1,3-1,4-1,5-1,6-or 1,7-prototropic shifts. These reactions are discussed in the context of a rigorous understanding of the chemistry of the ketene intermediates involved. Most of the work was published in the period 1980-2000 but important references to earlier literature are also included.

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Carboxy(vinyl)ketene intermediates in the thermolysis of methylthio- and methoxy-substituted Meldrum’s acid derivatives

Cited by 12 publications

References 31 publications

The Ajudazols A and B, Novel Isochromanones fromChondromyces crocatus (Myxobacteria): Isolation and Structure Elucidation

The Ajudazols A and B, Novel Isochromanones fromChondromyces crocatus (Myxobacteria): Isolation and Structure Elucidation

Mechanistic Evidence for an α-Oxoketene Pathway in the Formation of β-Ketoamides/Esters via Meldrum's Acid Adducts

Synthetic Applications of the Pyrolysis of Meldrum's Acid Derivatives

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