- Improvements in Diels-Alder cycloadditions with some acetylenic compounds under solvent-free microwave-assisted conditions: Experimental results and theoretical approaches
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The Diels-Alder irreversible cycloadditions of 1,3-cyclohexadiene 1, 3-carbomethoxy-2-pyrone 2 and 2-methoxythiophene 3 with acetylenic dienophiles under solvent-free conditions are described. By strict comparisons with conventional heating under similar conditions, important specific microwave effects are revealed in the two last cases whereas they are absent in the first one. They are discussed in terms of asynchronous mechanisms in agreement with ab initio calculations at the HF/6-31G(d) level indicating dissymmetries in transition states. Specific MW effects can be understood by considering the enhancements in dipole moments from ground states to transition states.
- Loupy, André,Maurel, Fran?ois,Sabatié-Gogová, Andrea
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p. 1683 - 1691
(2007/10/03)
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- Diels-Alder reaction of methoxythiophenes: A new one-pot synthesis of dimethyl phthalates
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A series of dimethyl phthalates have been prepared from methoxythiophenes and dimethyl acetylenedicarboxylate (DMAD) in xylene. When the reaction is carried out in acetic acid, thienylfumarates are obtained.
- Corral,Lissavetzky,Manzanares
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- Facile Interconversion of the Isomeric Acid Chlorides Derived from Half Methyl Esters of 3-Methoxyphthalic Acid
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The isomeric acid chlorides obtained by treating the half methyl esters of 3-methoxyphthalic acid with thionyl chloride interconvert so readily that it is not practical to isolate one acid chloride free of the other.At equilibrium the main isomer is the a
- Gupta, Dahmendra N.,Hodge, Philip,Hurley, Peter N.
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p. 391 - 394
(2007/10/02)
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- Syntheses of Highly Substituted Benzenes via Diels-Alder Reactions with 2H-Pyran-2-ones
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The 2H-pyran-2-ones (α-pyrones) 1 react as dienes in Diels-Alder reactions with acetylene derivatives.The primarely formed cycloadducts immediately aromatize to benzenes by CO2 elimination.Thus, methyl acetylenedicarboxylate (2a) gives dimethyl phthalates 3, and methyl acetylenediphosphonate (2b) gives dimethyl 1,2-phenylenediphosphonates 8.The reactions of 1-(dimethylamino)-1-methoxyethene (9) with 1 regioselectively produce N,N-dimethylanilines 10 and isomeric homophthalate derivatives 12.Naphthoquinones 14 could be generated from 1,4-benzoquinone (13) and 1 in the presence of acetic anhydride and Pd/C.Hydroxy-2H-pyran-2-ones 4 react via their trimethylsilyl ether 6 analogously with 2a to give dimethyl (trimethylsiloxy)phthalates 7 which are easily converted to phenols 5 by acid-catalyzed hydrolysis.
- Ziegler, Thomas,Layh, Marcus,Effenberger, Franz
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p. 1347 - 1356
(2007/10/02)
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- Regiospecific synthesis of anthracyclinone compounds such as daunomycinone
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A regiospecific synthesis for anthracyclinones asymmetric is disclosed. The synthesis is based upon a regiospecific bromination of the C-7 position of the α-tetralone which after transposing the keto group to the β-position and reaction with an organo-lithium compound is condensed with a phthalate ester.
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- (1E)-1,3-DIMETHOXY-1,3-BUTADIENE
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Reaction of 1,1-dimethoxy-2-butyne (II) with sodium methoxide in dimethyl sulfoxide at 100 deg C yields (1E)-1,3-dimethoxybutadiene (III) (20-30percent).The diene III undergoes ready Diels-Alder reaction with maleic anhydride, N-phenytriazolinedione and d
- Dowd, Paul,Weber, William
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p. 2155 - 2156
(2007/10/02)
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- Preparation and Reaction of Pyridones: Steric and Electronic Effects on Cycloadditions with 2(1H)-Pyridones
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The reactions of series of substituted 2(1H)-pyridones with dimethyl butynedioate have been studied.Cycloadditions across the 3,6-positions can be observed in certain instances and are particularly favoured where steric buttressing occurs between the substituent groups of the starting pyridones.The pyridone could not be induced to react with simple olefins, either by intermolecular or, via incorporation of alkenyl substituents, by intramolecular processes.From the results it is shown that 2-pyridones can be encouraged to behave as reactive classical dienes in cycloaddition reactions.
- Gisby, Graham P.,Royall, Sven E.,Sammes, Peter G.
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p. 169 - 174
(2007/10/02)
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- 1,4-dimethoxy-1,3-butadiene as a Donor Diene in Diels-Alder Cycloadditions
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The title compound (DMBU) is a useful diene in cycloadditions.Since DMBU is readily obtained in two steps from 1,4-dihydroxy-2-butyne, it should be regarded as an inexpensive and abundant starting material.Diels Alder products were obtained from DMBU and the dienophiles, dimethyl acetylenedicarboxylate, ethyl propiolate, benzyne, fumaronitrile, tetracyanoethene, maleic anhydride, 1,2-dibenzoylethene, diethyl azodicarboxylate, and four 1,4-quinones.The aromatization of some of these products was studied.As determined by gas chromatography and 1H NMR, DMBU is obtained as three isomers Z,Z/Z,E/E,E = (60 +/-3):(34 +/- 3):(6 +/- 2).While the Z,Z form is less reactive, the Z,E and E,E isomers react with tetracyanoethene at rates similar to that of 1-methoxy-1,3-butadiene.
- Hiranuma Hidetoshi,Miller, Sidney I.
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p. 5083 - 5088
(2007/10/02)
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- Synthesis of some bicyclooct-5-en-2-ones and bicyclooctan-2-ones. Rearrangement accompanying oxidative decarboxylation with lead tetraacetate
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1-Methoxy-2-methyl-1,4-cyclohexadiene (3), 2-methoxy-1-methyl-1,3-cyclohexadiene (2), and 2-methoxy-1,5,5-trimethyl-1,3-cyclohexadiene (14) on heating with maleic anhydride give 1-methoxy-endo-7-methylbicyclooct-5-ene-syn-2,3-dicarboxylic acid anhydride (7) and its 6-methoxy-1-methyl (16a) and 6-methoxy-1,8,8-trimethyl (16b) analogues, respectively.On hydrolysis 16a and 16b give the corresponding keto dicarboxylic acids, 18a and 18b, via keto anhydrides 17a and 17b.Treatment of 18b with lead tetraacetate gives 1,8,8-trimethylbicyclooct-5-en-2-one (19) together with products in which rearrangement to a bicyclooctane system has occured.Treatment of 17b with bis(triphenylphosphino)nickel dicarbonyl gives only 19; similar treatment of 17a gives 1-methylbicyclooct-5-en-2-one (1).Reaction of bicyclooctane-2,3-dione (27) with methyllithium gives 3-hydroxy-3-methylbicyclooctan-2-one (28), its dimer 31, and a diol 30.Treatment of 5-exo-acetoxy-1,5-endo-dimethyl-6-oxobicyclooctane-anti-2,3-dicarboxylic acid (37) with lead tetraacetate gives 3-endo-acetoxy-1,3-exo-dimethylbicyclooct-5-en-2-one (33) as a minor product; the major product is derived by rearrangement to a bicyclooctane system.It is proposed that this rearrangement, like that of 18b, involves oxidative decarboxylation of a single carboxylic acid group to give a carbonium ion that undergoes rearrangement via a 1,2-acyl migration.
- Yates, Peter,Langford, Gordon E.
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p. 344 - 355
(2007/10/02)
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