6-endo-dig Cyclization of heteroarylesters to alkynes promoted by Lewis acid catalyst in the presence of Brønsted acid

Hellal, Malik; Bourguignon, Jean‐Jacques; Bihel, Frédéric

doi:10.1016/j.tetlet.2007.11.020

Cited by 80 publications

(48 citation statements)

References 27 publications

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“…Hellal et al [130] have reported an efficient approach for the synthesis of novel series of isocoumarins under strong acidic conditions using TFA as solvent. The process consisted of a Michael-type (6-endo-dig) cyclization of various heterocyclic esters by employing a combination of Brønsted and Lewis acid catalysts.…”

Section: Benzopyrones: Coumarins and Chromonesmentioning

confidence: 99%

Microwave-Assisted Synthesis of Bioactive Six-Membered Heterocycles and Their Fused Analogues

et al. 2016

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This review describes the formation of six-membered heterocyclic compounds and their fused analogues under microwave activation using modern organic transformations including cyclocondensation, cycloaddition, multicomponents and other modular reactions. The review is divided according to the main heterocycle types in order of increasing complexity, starting with heterocyclic systems containing one, two and three heteroatoms and their fused analogues. Recent microwave applications are reviewed, with special focus on the chemistry of bioactive compounds. Selected examples from the 2006 to 2015 literature are discussed.

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Section: Benzopyrones: Coumarins and Chromonesmentioning

confidence: 99%

Microwave-Assisted Synthesis of Bioactive Six-Membered Heterocycles and Their Fused Analogues

et al. 2016

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“…Here, a Lewis acid catalyst is needed to facilitate the addition [13]. The final oxidative aromatization needs an oxidation reaction, which forms the desired pyridine (5) but impede the formation of appropriate pyridine N-oxides.…”

Section: A-substituted Pyridine Synthesismentioning

confidence: 99%

Heterogeneous Catalyzed Pyridine Synthesis using Montmorillionite and Nanoparticle‐Impregnated Alumina in a Continuous Micro Flow System

Abahmane¹,

Knauer²,

Ritter³

et al. 2009

Chem Eng & Technol

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The synthesis of pyridine derivatives was investigated using a combined micro flow-through system. Therefore, two different heterogeneous catalyst assemblies were used subsequently under different temperature conditions. The investigated pyridine synthesis method includes three reaction steps: at first, an enamine has to be formed by a condensation reaction of methyl ketone and propargylamine. Secondly, a pericyclic reaction of the enamine is needed to form dihydropyridine derivatives. Finally, the dihydropyrimidines received have to be oxidized to yield the desired pyridine derivative. The propargylamine used tends towards side reactions even if activating catalysts are present at elevated temperatures. To reach high yields for the overall process, each reaction step demands for a specific catalyst and suited reaction conditions. Hence, the reaction sequence was separated into two consecutive steps. For the initial condensation reaction, montmorillionite was investigated as heterogeneous catalyst. For the subsequent reaction steps, different types of nanoparticles impregnated on alumina were investigated as oxidation catalyst, using air as oxidation agent. Here, the results and optimized process conditions for the conversion of aliphatic and aromatic methyl ketones are presented. As a result, the separation of the reaction steps by application of the two-step microreactor system leads to a significant improvement of the process performance. The reaction time was reduced significantly to about 20 minutes without reduction of the product turnover in several cases.

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“…To the best of our knowledge, the use of halogenopyridine derivatives has not been fully explored in this process: only three examples of the synthesis of 7-aryl-5H-pyrano [4,3-b]pyridin-5-one, resulting from a copper-or gold-catalyzed/Lewis acid mediated 6-endo-dig intramolecular cyclization under microwave (MW) irradiation of the corresponding methyl or ethyl 2-(2-arylethynyl)nicotinates (¼ methyl or ethyl 2-(2-arylethynyl)pyridine-3-carboxylic acids), have already been described by Bihel and co-workers [7] (Scheme 2). However, in this reaction, they have synthesized and isolated the Sonogashira product separately.…”

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confidence: 99%

“…Recently, Pal has shown that during the optimization of the reaction conditions for the Pd/C-mediated synthesis of an isocoumarin, the corresponding phthalide was isolated as the major product when 1,4-dioxane was used as solvent [9]. Thus, with the Pd/CÀPh 3 PÀCuI system and Et 3 N in 1,4-dioxane ( Table 1, Entry 1), the 4-azaphthalide (7Z)-7-benzylidenefuro[3,4-b]pyridin-5(7H)-one (1a) was obtained as the major product and the 5-azaisocoumarin 7-phenyl-5H-pyrano [4,3-b]pyridin-5-one (1b) [7] as the minor product, via a 5-exo-dig and a 6-endo-dig cyclization of the Sonogashira intermediate, respectively. No reaction was observed in DMF or toluene.…”

mentioning

confidence: 99%

“…From 1-ethynyl-3-methoxybenzene ( Table 2, Entry 1), 4-azaphthalide 2a was formed in good yield (55%), and only traces of the corresponding 5-azaisocoumarin 2b were obtained. With 1-ethynyl-4-methoxybenzene, 4-azaphthalide 3a was the major product (44%), but 5-azaisocoumarin 3b [7] was also isolated in 26% yield ( Table 2, Entry 2). These two results corroborate the observation made by Kanazawa and Terada [10] for the organic base-catalyzed intramolecular cyclization, according to which the presence of electron-donating groups at the phenyl ring of the Sonogashira products diminish the electrophilic nature at the b-position of the triple bond, thus favoring the formation of the 5-exo-dig cyclized products.…”

mentioning

confidence: 99%

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Tandem Palladium/Charcoal‐Copper(I) Iodide (Pd/C‐CuI) Catalyzed Sonogashira Coupling and Intramolecular Cyclization from 2‐Bromonicotinic Acid (=2‐Bromopyridine‐3‐carboxylic Acid) and Ethynylarenes to 4‐Azaphthalides (=Furo[3,4‐b]pyridin‐5(7H)‐ones) and 5‐Azaisocoumarins (=5H‐Pyrano[4,3‐b]pyridin‐5‐ones)

Begouin¹,

Queiroz²

2011

Helvetica Chimica Acta

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Several 4-azaphthalides (¼ furo [3,4-b]pyridin-5(7H)-ones) and 5-azaisocoumarins (¼ 5H-pyrano[4,3-b]pyridin-5-ones) were prepared through a tandem heterogeneous Pd/C-mediated Sonogashira coupling and a 5-exo-dig or 6-endo-dig intramolecular cyclization of 2-bromonicotinic acid (¼ 2-bromopyridine-3-carboxyclic acid) with various ethynylarenes or 3-ethynylthiophene. In the presence of Pd/CÀPh 3 PÀCuI and Et 3 N in dry dioxane under Ar at 908, a mixture of 4-azaphthalides (usually the major product) and 5-azaisocoumarins was obtained after 3.5 h under normal heating (Schemes 3 and 4; Tables 1 and 2). This mixture of compounds was also obtained with the same catalytic system under microwave (MW) irradiation in only 25 min (Tables 3 and 4). The 1-ethynyl-3-methoxybenzene gave on heating only the corresponding 4-azaphthalide (Table 2), while under MW irradiation, both the 5-exo-dig and the 6-endo-dig products were obtained ( Table 4). For the 3-ethynylthiophene, the regioselectivity for the corresponding 4-azaphthalide was achieved with both methods (Tables 2 and 4). Although the yields and the regioselectivity of the reaction generally remained the same with both methods, the use of MW allowed us to obtain the corresponding products in a shorter reaction time. From 4-ethynyl-N,Ndimethylaniline (¼ 4-ethynyl-N,N-dimethylbenzenamine), the corresponding 4-azaphthalide and 5-isocoumarin were only obtained under MW irradiation (Tables 2 and 4). To the best of our knowledge, it is the first time that this kind of tandem reaction was applied to a pyridine derivative giving the corresponding 4-azaphthalides and 5-azaisocoumarins which are easily separated and may both show biological activity.Introduction. -Phthalides (¼ isobenzofuran-1(3H)-ones) [1] and isocoumarins (¼ 1H-2-benzopyran-1-ones) [2] are important classes of O-containing heterocycles often seen in naturally occurring and biologically active compounds. One of the most attractive routes for the synthesis of these compounds is the use of 2-halogenobenzoic acids and terminal alkynes as starting materials. Usually, this process was performed in a one-pot two-step reaction: a Sonogashira coupling [3] of 2-iodobenzoic acid with terminal alkynes followed by an intramolecular cyclization of the 2-alkynylbenzoic acid, which often results in a mixture of a (3Z)-3-alkylidenephthalide, and a 3-alkyl-or 3-arylisocoumarin via 5-exo-dig and 6-endo-dig cyclizations, respectively (Scheme 1) [4]. Kundu and co-workers described this heteroannulation process as stereospecific for the phthalide, since only the (3Z)-isomers of the 3-alkylidenephthalides were obtained [4a].

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6-endo-dig Cyclization of heteroarylesters to alkynes promoted by Lewis acid catalyst in the presence of Brønsted acid

Cited by 80 publications

References 27 publications

Microwave-Assisted Synthesis of Bioactive Six-Membered Heterocycles and Their Fused Analogues

Microwave-Assisted Synthesis of Bioactive Six-Membered Heterocycles and Their Fused Analogues

Heterogeneous Catalyzed Pyridine Synthesis using Montmorillionite and Nanoparticle‐Impregnated Alumina in a Continuous Micro Flow System

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