Regioselective Synthesis of 2(1<i>H</i>)-Pyridinones from β-Aminoenones and Malononitrile. Reaction Mechanism

Alberola, A.; Calvo, Luis; Ortega, Alfonso González; Ruíz, and M. Carmen Sañudo; Yustos, Pedro; García-Granda, Santiago; Garcia-Rodriguez, Esther

doi:10.1021/jo991121o

Cited by 62 publications

(20 citation statements)

References 25 publications

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“…On the other hand the formation of 1,2,3-thiadiazole-4-carboxamides in the reaction of pyranone 1a with piperidine and primary amines [28] can be rationalised by an initial nucleophilic attack at C-4 prior to ring opening (Scheme 3), which is in line with the accepted mechanism of the Dimroth rearrangement. [30,31] It was demonstrated earlier [32,33] that reactions between ketenes and nucleophiles, pyridine in particular, take place at extremely low temperatures (15-40 K), to generate ketene-pyridine zwitterions. The kinetic monitoring of such reactions revealed that they have extremely low activation enthalpies (approx.…”

Section: Resultsmentioning

confidence: 98%

Synthetic and Theoretical Aspects of New Dimroth Rearrangement of6‐Aminopyran‐2‐ones to 6‐Hydroxypyridin‐2‐ones via Carbamoyl Ketenes

Subbotina¹,

Fabian

Tarasov³

et al. 2005

Eur J Org Chem

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Two alternative directions for thermal transformation of 6-amino-4-oxopyrano [3,4-d] [1,2,3]thiadiazoles 1, leading either to 6-hydroxy-4-oxo-[1,2,3]thiadiazolo[4,5-c]pyridines 2 or 2-cyano-2-(1,2,3-thiadiazol-5-yl)acetamide 4b, were observed. The first one represents a new, Dimroth-type rearrangement and proceeds by thermal opening of the pyrane ring, followed by the simultaneous rotational isomerization of the ketene intermediate 7 (s-cis) to 7 (s-trans) and its recyclization onto the amido group to form the pyridin-2-one cycle. The first step of the rearrangement has a calculated [B3LYP/ 6-31G(d)] activation barrier of 24-34 kcal/mol, the involve-

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Section: Resultsmentioning

confidence: 98%

Synthetic and Theoretical Aspects of New Dimroth Rearrangement of6‐Aminopyran‐2‐ones to 6‐Hydroxypyridin‐2‐ones via Carbamoyl Ketenes

Subbotina¹,

Fabian

Tarasov³

et al. 2005

Eur J Org Chem

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“…Pure samples of the enaminoketones 157 were prepared by stirring an alcoholic solution of the alkynone 156 with secondary amine for two hours. These enaminoketones when refluxed with excess of diethylamine formed benzopyrones 158 (Figure 58) [108].The identification of some intermediates of the reactions between β-aminoenones and malonitrile to give 2(1H) -pyridinones had been allowed to obtain valuable information concerning its mechanism [109]. These reactions began with a conjugated addition of the nitrile to the enone followed by elimination.…”

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confidence: 99%

“…The opening of the iminopyrone 161 must lead to (2Z) 162, but the configuration of the intermediates 1 6 2, isolated and identified by X-ray, is 2E [109]. On the other hand, the formation of product 163 starting from 159 demands that the last process of the conjugated addition-elimination takes place in the isomer (2Z) 162.…”

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confidence: 99%

Recent development in preparation reactivity and biological activity of enaminoketones and enaminothiones and their utilization to prepare heterocyclic compounds

Negri

Kascheres

2004

Journal of Heterocyclic Chem

179

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Enaminoketones and esters are gaining increased interest, particularly cyclic-β-enaminoesters, which are known as important intermediates for the synthesis of heterocycles and natural products, because the enantioselective preparation of highly functionalized compounds is of central importance in synthetic chemistry. Enaminones are versatile synthetic intermediates that combine the ambident nucleophilicity of enamines with the ambident eletrophilicity of enones. Enaminoketones and enaminonitriles have proven to be versatile building blocks for the synthesis of various heterocycles such as pyridine, pyrimidine and pyrrole derivatives. Enaminones systems have "enone" character, and may act as acceptors in both 1,2 and 1,4-additions. In this way the enaminone serves as a scaffold for annulation, and can gain access to systems such as pyrroles indolizidines, quinolizidines and perhydroindoles, all of which are common motifs in alkaloid structures. Enaminones are frequently employed as building blocks for the preparation of a variety of bicyclic compounds of biological interest and have been recently recognized as potential anticonvulsant compounds. Since a large number of developments in the use of enaminones in heterocyclic synthesis have occurred, a review of the recent developments in the synthetic approaches, covering the literature since 1995 until 2004, to these interesting molecules and their useful chemical transformations and biological activity can be considered of considerable value.J. Heterocyclic Chem., 41, 461 (2004).Enaminoketones. Introduction.The term enaminone was introduced by Greenhill to define the enamine of a 1,3-diketone, β-ketoester or similar 1,3-difunctional reagents, and is used to indicate any compound containing the conjugated system N-C=C-C=O [1]. Enaminones are versatile synthetic intermediates that combine the ambident nucleophilicity of enamines with the ambident eletrophilicity of enones. The chemistry of the enaminocarbonyl group 1 is potentially an area of considerable scope when one considers that there are present in this moiety, three nucleophilic sites (a, c and e) and two electrophilic sites (b and d) [2][3][4] (Figure 1).Theorically, primary and secondary acyclic enaminones can exist in three tautomeric forms: ketamino form, iminoenol form and oxoimino form [1][2][3]. There is also evidence that cyclic enaminones exist primarily in the enaminoketo form. A study of cyclic enaminoketones shows that these compounds have a significant steric fator in the six-membered ring. The six-membered ring enaminoketones are only slightly stronger bases than the saturated amines, whereas five-and-seven membered rings are much stronger bases than saturated amines. This has been attributed to a large steric strain present in six-membered enaminoketones [5].β-Aminoenones or enaminoketones can exist in four conformations owing to restricted rotations around the C=C double and C-C=O single bonds [3]. Enaminones with primary or secondary amino groups can exist in both Z-and E-forms. If there is a...

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“…A nu mber of methods have been described for the preparation of β-enamino carbonylic compounds [5][6][7][8], such as condensation of amines with β-dicarbonylic compounds in aromat ic solvents with azeotropic water removal [9] or Raney-Ni hydrogenation of isoxazoles [6]. However, these methods require high pressure and temperature [10]. The use of low boiling amines is particularly problemat ic.…”

Section: Introductionmentioning

confidence: 99%

Aluminum Phosphate Catalyzed Free Solvent Preparation of β-enamino Esters

Harrad¹,

Boualy²,

Firdoussi³

et al. 2012

CHEMISTRY

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Alu minu m phosphate (AlPO 4 ) efficiently catalyzed the condensation of 1,3-ketoesters with primary amines under free solvent conditions. The catalyst has been prepared and characterized by powder XRD and FT-IR studies. The AlPO 4 synthesis was performed in water at roo m temperature fro m AlCl 3 and H 3 PO 4 in the presence of ammonia solution. Resultant material showed good catalytic efficiency in condensation of 1,3-ketoesters with primary amines using a domestic micro wave oven with no solvent. The reaction was complete in 7 min to afford β-enamino esters in a high yield and high selectivity.

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Regioselective Synthesis of 2(1H)-Pyridinones from β-Aminoenones and Malononitrile. Reaction Mechanism

Cited by 62 publications

References 25 publications

Synthetic and Theoretical Aspects of New Dimroth Rearrangement of6‐Aminopyran‐2‐ones to 6‐Hydroxypyridin‐2‐ones via Carbamoyl Ketenes

Synthetic and Theoretical Aspects of New Dimroth Rearrangement of6‐Aminopyran‐2‐ones to 6‐Hydroxypyridin‐2‐ones via Carbamoyl Ketenes

Recent development in preparation reactivity and biological activity of enaminoketones and enaminothiones and their utilization to prepare heterocyclic compounds

Aluminum Phosphate Catalyzed Free Solvent Preparation of β-enamino Esters

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