Tandem Conjugate Carbon Addition–Intermolecular Hetero Diels–Alder Reactions using Ethyl 1H-Perimidine-2-acetate as a Ketene Aminal with Heating or Microwave Activation†

Cado, F.; Bazureau, Jean Pierre; Hamelin, J.; Jacquault, P.; Dozias, Marie‐Joelle

doi:10.1039/a701052d

Cited by 12 publications

(4 citation statements)

References 11 publications

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“…Thus, Bazureau described the cycloaddition of a 1-azadiene derived from a vinylpyrimidine (23) as a tandem conjugate addition/hetero-DielsϪAlder reaction (Scheme 8). [33] Scheme 8…”

Section: Reactions Without Supportmentioning

confidence: 99%

“…Microwave irradiation has been used to improve reactions of heterodienophiles [40,62] and heterodienes [33,35,38,63] with low reactivities. Motorina described the intramolecular heteroDielsϪAlder reaction of N-alkyl-2-cyano-1-azadienes (71) (Scheme 24); [63] although the reaction had already success- Scheme 24 A. de la Hoz, A. Díaz-Ortis, A. Moreno, F. Langa fully been performed by heating the reactants in benzene overnight in a sealed tube at 110°C, it was found that reaction time could be reduced to 14 min in a microwave oven.…”

Section: Scheme 23mentioning

confidence: 99%

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Cycloadditions under Microwave Irradiation Conditions: Methods and Applications

et al. 2000

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Microwave irradiation has been applied with success to cycloaddition reactions. The special characteristics of such irradiation entails the use of new methodologies, including equipment, glassware, solvents, and solid supports. All of these aspects are described in this review. Under classical heating conditions, these reactions usually require long reaction times, high temperatures, and/or Lewis acid catalysts, resulting in partial or total decomposition of sensitive compounds. This is a particularly significant problem in the synthesis of natural products. These problems have been conveniently overcome by the use of microwave irradiation. The short reaction time associated with microwave activation avoids decomposition of reagents and products, and prevents polymerization of the diene or dienophile. Heterocyclic compounds have been synthesized by cycloaddition reactions, or have been observed to react as dienes and dipoles under microwave irradiation conditions. Even those heterocyclic systems that are very reluctant to participate in cycloaddition reactions, such as pyrazoles, can be induced to react under microwave irradiation conditions. The application of this method to the chemistry of [60]fullerene has permitted derivatization of this system while avoiding the problems of polycycloaddition and cycloreversion. In most cases, spectacular accelerations and great improvements in yields and reaction conditions are observed. Finally, in some cases, changes in the chemo‐, regio‐, or stereoselectivity have been observed. These changes have been connected with the absolute hardness of the transition state, with the harder state being favored under microwave irradiation conditions. Microwave chemistry thus opens new possibilities for modifying the result of competitive reactions by considering the relative hardness of the transition states.

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“…Thus, Bazureau described the cycloaddition of a 1-azadiene derived from a vinylpyrimidine (23) as a tandem conjugate addition/hetero-DielsϪAlder reaction (Scheme 8). [33] Scheme 8…”

Section: Reactions Without Supportmentioning

confidence: 99%

Section: Scheme 23mentioning

confidence: 99%

Cycloadditions under Microwave Irradiation Conditions: Methods and Applications

et al. 2000

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“…Similarly, Motorina described the intramolecular hetero-Diels±Alder reaction of Nalkyl-2-cyano-1-azadienes 86 (Scheme 9.26) [76]; although the reaction had already been performed by heating the reactants in benzene overnight in a sealed tube at 110 8C, it was found that reaction time could be reduced to 14 min in a microwave oven at 650 W. Bazureau described a tandem conjugate addition±intermolecular hetero-Diels±Alder reaction of perimidine derivatives under solvent-free conditions with focused microwave irradiation [77]. The main feature of this reaction was attainment of complete addition in less than 8 min.…”

Section: Heterodienesmentioning

confidence: 99%

Microwaves in Cycloadditions

Hoz

Díaz‐Ortiz

Langa³

2002

Microwaves in Organic Synthesis

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The first examples of microwave-induced reactions were cycloadditions and pericyclic reactions performed under pressure, because of the use of domestic ovens, to avoid the risk of igniting flammable solvents (Scheme 9.1) [11,12].Reactions were performed in sealed thick-walled glass tubes or in Teflon acid-digestion vessels, in domestic microwave ovens [13]. Teflon vessels can be used at pressures up to 14 atm, at temperatures below 250 8C, and are resistant to most commonly used chemicals, although they deform at temperatures >250 8C.The lack of temperature and pressure control in these systems could lead to safety problems, because of overpressure resulting from the heating rate caused by microwaves. These problems can be reduced by using solvent-free methodology, which also enables the use of larger quantities of reagents. Yields have been greatly improved, and reaction times reduced, in comparison with conventional procedures in solvents under reflux.These reactions were next revisited by Strauss and it was shown that, under identical conditions in xylene, the reaction rates were strictly identical within experimental error [14]. Reactions under RefluxReactions involving a solvent under reflux require the use of modified commercial microwave ovens. In these modified systems the oven is perforated on the top to accommodate a reflux condenser and a 10 cm pipe is used to avoid microwave leakage; the turnable dish is replaced by a magnetic stirrer or by monomode reactors especially designed for chemical synthesis [15].The advantage of reactions involving solvent is that the reaction temperature is controlled by the reflux temperature of the solvent [16]. It should, however, be re-296 9 Microwaves in Cycloadditions CO 2 Me MeO 2 C MeO 2 C CO 2 Me MICROWAVE 10 min p-xylene, 87% 325º<361 ºC CONTROL 4 h p-xylene, 67% 138 ºC 1 2 3 Scheme 9.1 297 9.3 Solvent-free Conditions 5 6 7 8 Scheme 9.2 silica gel [29] and alumina [30]have also been used to generate 1,3-dipoles and, in this way, heterocyclic compounds can be obtained in a one-pot procedure. In these reactions changes in the regioselectivity of the reaction have not been observed under the action of microwave irradiation. Reactions without SupportAn alternative to the use of supported reagents is the use of uncatalyzed ªneat reactionsº. Under these conditions the radiation is absorbed directly by the reagents and this results in spectacular acceleration, higher yields and purity of the reaction products, a simple workup procedure, and sometimes changes in the selectivity of the cycloaddition. Diels±Alder reactions [31] and 1,3-dipolar cycloadditions [32,33] have been performed by use of this methodology. For example, DÌaz-Ortiz described the hetero-Diels±Alder and 1,3-dipolar cycloaddition reactions of ketene acetals. The reactions were improved and products were isolated directly from the crude reaction mixture without polymerization of the ketene acetals [34].When the enantiomerically pure ketene acetal 16 was used, cycloaddition with N,a-diphenylnitrone (11) or ...

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“…Mohammed Aït Ameur Meziane, a Mustapha Rahmouni, a Jean Pierre Bazureau, b* Jack Hamelin b a Centre Universitaire de Tiaret [C.U.T. ], 14000 Tiaret, Algérie b Synthèse et Electrosynthèse Organiques 3, UMR-CNRS N˚6510, Université de Rennes 1, Campus de Beaulieu, Avenue du Général Leclerc, F-35042 Rennes Cédex, France Fax +33 299286374; E-mail: Jean-Pierre.Bazureau@univ-rennes1.fr Received 10 November 1997;revised 20 January 1998 synthesis in anhydrous media 9 or using solvent-free conditions 10 under focused microwave irradiation, 11 we have obtained 3 from a mixture of 2 and N , N -dimethylformamide diethyl acetal (DMF-DEA) which was submitted to focused microwave irradiation at 90°C 6 during 15 minutes (Scheme). Compound 3 was obtained in 82% yield after recrystallization.…”

Section: A New Route To 1-oxo-12-dihydropyrimido[16-a ]Benzimidazolmentioning

confidence: 99%

A New Route to 1-Oxo-1,2-dihydropyrimido[1,6-a]benzimidazole-4-carboxylates from Ethyl 2-(Benzimidazol-2-yl)-3-(dimethylamino)acrylate Using Solvent-Free Conditions

Meziane¹,

Rahmouni²,

Bazureau³

et al. 1998

Synthesis

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Ethyl 2-(Benzimidazol-2-yl)-3-(dimethylamino)acrylate ( 3 ) has been used as starting material to develop a mild, efficient solvent-free preparation of ethyl 1-oxo (or thioxo)-1,2dihydro-pyrimido[1,6-a ]benzimidazol-4-carboxylates 6 (X = O, S) from a variety of isocyanates 4b-d and isothiocyanates 4a , e,f , in yields ranging from 52 to 82%. The synthesis of the starting benzimidazole 3 (82% yield) without solvent, assisted by focused microwave irradiation, is also reported.

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Tandem Conjugate Carbon Addition–Intermolecular Hetero Diels–Alder Reactions using Ethyl 1H-Perimidine-2-acetate as a Ketene Aminal with Heating or Microwave Activation†

Cited by 12 publications

References 11 publications

Cycloadditions under Microwave Irradiation Conditions: Methods and Applications

Cycloadditions under Microwave Irradiation Conditions: Methods and Applications

Microwaves in Cycloadditions

A New Route to 1-Oxo-1,2-dihydropyrimido[1,6-a]benzimidazole-4-carboxylates from Ethyl 2-(Benzimidazol-2-yl)-3-(dimethylamino)acrylate Using Solvent-Free Conditions

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