Dimerization of Sodium Enolates of Malonic Ester and Acetylacetone Effected by the Action of 4-Methyl-3,4-dibromotetrahydropyran

Gevorkyan, A. A.; Arakelyan, A. S.; Barsegyan, S. V.; Petrosyan, K. A.; Panosyan, G. A.

doi:10.1023/b:rujo.0000010200.00341.d0

Russian Journal of Organic Chemistry

2003

DOI: 10.1023/b:rujo.0000010200.00341.d0

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Dimerization of Sodium Enolates of Malonic Ester and Acetylacetone Effected by the Action of 4-Methyl-3,4-dibromotetrahydropyran

A. A. Gevorkyan

A. S. Arakelyan

S. V. Barsegyan

et al.

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Cited by 4 publications

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“…[13], is not followed in reactions with enolates derived from b-dicarbonyl compounds [4]. In the latter case, dehydrodimers IV of b-dicarbonyl compounds (path 2) and dihydropyran V are formed instead of cross-coupling products III.…”

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“…Let us demonstrate once more the possibilities of the proposed approach by revealing the reason for dehydrodimerization of sodium enolates by the action of dibromide I as an example [4]. We start the discussion by noting that since the discovery of nucleophilic radical substitution [510] some authors presumed classical nucleophilic substitution to be a process including two steps of transfer of one electron.…”

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Alkylation of 3,4-Dibromo-4-methyltetrahydropyran with Diethyl Malonate as a Key to Understanding the Electronic Nature of Chemo- and Regioselectivity of Molecules

et al. 2005

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The reaction of 3,4-dibromo-4-methyltetrahydropyran with diethyl malonate in the presence of sodium butoxide leads to formation of the corresponding cross-coupling product rather than of tetraethyl ethane-1,1,2,2-tetracarboxylate (product of dehydrodimerization of diethyl malonate) which is formed in the presence of sodium ethoxide. An explanation was proposed, which may be regarded as a key to understanding the nature of the driving force for one-and two-electron transfer, as well as chemo-and regioselectivity of organic molecules.It was recently shown that the dehydrobromination substitution pattern (Scheme 1, path 1: I g II g III), which is typical of reactions of 3,4-dibromo-4-methyltetrahydropyran (I) with a series of nucleophiles (such as amines, phenols, alcohols, organic acid salts, etc.) [13], is not followed in reactions with enolates derived from b-dicarbonyl compounds [4]. In the latter case, dehydrodimers IV of b-dicarbonyl compounds (path 2) and dihydropyran V are formed instead of cross-coupling products III. It may seem that we revealed just one more example of radical nucleophilic substitution whose general relations have long been known [510].However, it becomes clear that this fact also contains important information on both driving forces of radical nucleophilic substitution itself and chemo-and regiochemistry of molecules on the whole [1113]. This information can be revealed by considering the problem in terms of the ion-pair version of mechanisms of organic reactions, which distinctly differentiates the roles of reagent and substrate [1420]. Without going into details (for more information, see [1518]), we should note that such refinement of the behavior of a reagent and a substrate rules out possible arbitrary treatment of nucleophilic or electrophilic properties of reagents [1113]. Another specific feature of the above version is that it implies the charge on an atom in a reagent, estimated in the chemical bond ionic character units, as a measure of the ability of a Cnucleofuge bond to undergo heterolysis and the degree of extension of the Cnucleofuge bond in the substrate as a measure of regio-and stereochemistry [1618]. In addition, it is believed that heterolytic dissociation of a Cnucleofuge bond is a three-rather than two-step process, each step corresponding to one type of ion pairs. These types include contact, loose, and solventseparated ion pairs (IP c , IP l , and IP ss ), the two latter possessing electrophilic properties [16]. Each type of ion pairs is characterized by specific regio-and stereochemical transformations, regardless of the type of chemical bond and transformation mode.Success of the approach is achieved due to the fact that the most important source of information on the nature of the driving force of a reaction is the product structure. This belief originates from the assumption that structure of a molecule contains so much important and reliable information on the properties of its precursors (ion pairs and molecules as a whole) that cannot be obtained b...

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Alkylation of 3,4-Dibromo-4-methyltetrahydropyran with Diethyl Malonate as a Key to Understanding the Electronic Nature of Chemo- and Regioselectivity of Molecules

et al. 2005

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Dimerization of Sodium Enolates of Malonic Ester and Acetylacetone Effected by the Action of 4‐Methyl‐3,4‐dibromotetrahydropyran.

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Polycarboxylic acids and esters P 0253Dimerization of Sodium Enolates of Malonic Ester and Acetylacetone Effected by the Action of 4-Methyl-3,4-dibromotetrahydropyran. -Reaction of the title compounds (I) and (II) affords the dimerization products (III) instead of the substituted pyrans (IV). In this case, dibromide (II) seems to act as oxidant which is converted to 4-methyl-2H-dihydropyran. -(GEVORKYAN, A. A.; ARAKELYAN, A. S.; BARSEGYAN, S. V.; PETROSYAN, K. A.; PANOSYAN, G. A.; Russ.

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A comprehensive picture of the one-electron oxidation chemistry of enols, enolates and α-carbonyl radicals: oxidation potentials and characterization of radical intermediates

Schmittel

Lal

et al. 2009

Tetrahedron

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Dimerization of Sodium Enolates of Malonic Ester and Acetylacetone Effected by the Action of 4-Methyl-3,4-dibromotetrahydropyran

Cited by 4 publications

References 1 publication

Alkylation of 3,4-Dibromo-4-methyltetrahydropyran with Diethyl Malonate as a Key to Understanding the Electronic Nature of Chemo- and Regioselectivity of Molecules

Alkylation of 3,4-Dibromo-4-methyltetrahydropyran with Diethyl Malonate as a Key to Understanding the Electronic Nature of Chemo- and Regioselectivity of Molecules

Dimerization of Sodium Enolates of Malonic Ester and Acetylacetone Effected by the Action of 4‐Methyl‐3,4‐dibromotetrahydropyran.

A comprehensive picture of the one-electron oxidation chemistry of enols, enolates and α-carbonyl radicals: oxidation potentials and characterization of radical intermediates

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