Trimethoxyphenylverbindungen, VIII<sup>1)</sup> Borheterocyclen in der präparativen Naturstoffchemie; Synthese des Baeckeols<sup>2)</sup>

Schiemenz, G. P.; Schmidt, Uwe

doi:10.1002/jlac.197619760739

Cited by 23 publications

(11 citation statements)

References 18 publications

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“…The analysis of the results showed that the highest yields were obtained with substrates bearing electron‐donating groups such as alkoxy substituents on the aromatic ring (Table 3, entries 6, 7 and 22‐2‐8). It is indeed gratifying to note that the reaction conditions are mild enough since they do not induce any dealkylation of an ether group located at an ortho position to the introduced acyl group (Table 3, entry 7) as observed in the acylation reaction with carboxylic acid catalyzed by BF 3 20…”

Section: Resultsmentioning

confidence: 96%

Catalytic Friedel–Crafts Acylation and Benzoylation of Aromatic Compounds Using Activated Hematite as a Novel Heterogeneous Catalyst

et al. 2010

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Catalytic Friedel-Crafts acylation of benzene and unactivated benzenes such as chlorobenzene and nitrobenzene have been successfully carried out using activated hematite (a-Fe 2 O 3 ) as a new, heterogeneous and green catalyst. Sonication of neat aFe 2 O 3 in a water bath under air atmosphere at room temperature followed by heating at 200 8C, dramatically increase the activity of a-Fe 2 O 3 . With the catalyst loading as low as 5.0 mol%, a wide variety of benzene derivatives were easily converted into the corresponding acylated products in a clean and highyielding acylation reaction. It was found that the activated a-Fe 2 O 3 could be efficiently recycled and reused several times by simple washing with ethyl acetate, this cannot be attained with most of the traditional catalysts.

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Section: Resultsmentioning

confidence: 96%

Catalytic Friedel–Crafts Acylation and Benzoylation of Aromatic Compounds Using Activated Hematite as a Novel Heterogeneous Catalyst

et al. 2010

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“…The reaction conditions are mild enough not to induce any dealkylation of an ether residue ortho to the introduced acyl group (Table 2, entry 11) as observed in the acylation reaction with carboxylic acid catalyzed by BF 3 . 3 Although the use of graphite for acylation of active aromatic compounds has been reported previously, 13 our new method, using a mixture of graphite and MeSO 3 H, offers significant improvements over the earlier method, reducing the reaction time considerably (20 minutes compared to eight hours), minimizing the amount of graphite from 1 g to 0.1 g, increasing the yield remarkably, and above all, using both electron donating and specially withdrawing substituted carboxylic acids instead of using the expensive and polluting acid halides that require special procedures in handling and working up.…”

Section: According Tomentioning

confidence: 99%

“…In order to minimize this problem, some catalytic Friedel-Crafts acylations have been developed recently. 2 In addition, acylations involving carboxylic acids and less toxic Lewis acids 3 or apparently non-hazardous acid catalysts 4 have been studied, although these procedures are not quite successful as practical and general synthetic methods. For instance, a methodology 4b of acylation of anisole with carboxylic acids over HZSM-5 zeolite, although environmentally safe, has limitations with regard to generality (no reaction with higher acids) and efficiency (reaction time of 48 h and concomitant Oacylation).…”

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confidence: 99%

Simple and Improved Procedure for the Regioselective Acylation of Aromatic Ethers with Carboxylic Acids on the Surface of Graphite in the Presence of Methanesulfonic Acid

Hosseini‐Sarvari¹,

Sharghi²

2004

Synthesis

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“…32) [60]. Dealkylation of an ether residue ortho to the introduced acyl group is frequently encountered, as in the synthesis of baeckeol (Eq.…”

Section: Friedel-crafts Acylation Reactionsmentioning

confidence: 99%

Achiral B(III) Lewis Acids

Ishihara¹

2000

Lewis Acids in Organic Synthesis

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The classical boron Lewis acids, BX3, RBX2 and R2BX (X = F, C1, Br, I, OTf) are now popular tools in organic synthesis. B(II1) can act as a Lewis acid because there is an empty p-orbital on the boron. Enthalpy values indicate that when pyridine is the reference base, the Lewis acidity of Group IIIB halides increase in the order A1X3 > BX3 > GaX3. The Lewis acidity of BX3 generally increases in the order fluoride < chloride < bromide < iodide, i.e. the exact reverse of the order expected on the basis of the relative o-donor strengths of the halide anions. The main reason for this anomaly is that in these BX3 compounds, the B-X bonds contain a n-component which is formed by overlap of a filled p-orbital on the halogen with the empty p-orbital on the boron. Because the latter orbital is used to form an o-bond when BX3 coordinates with a Lewis base, this n-component is completely destroyed by complex formation. The strength of the n-component now increases in the order iodide < bromide < chloride < fluoride, i.e. the amount of n-bond energy that is lost on complex formation increases as the atomic weight of the halogen decreases. Evidently, as far as the extent of complex formation is concerned, this is a more important factor than the corresponding decrease in the o-donor strength of the halogen.The BF3 and BC13 complexes of diethyl ether are less stable than those of dimethyl ether, and the same order of stability is observed for the complexes of diethyl and dimethyl sulfides. As expected, steric interaction decreases as the distance between the metal and ligand atom is increased. Thus, it decreases when the metal atom is changed from boron to aluminum, or when the ligand atom is changed from oxygen to sulfur.The major applications of BX3 Lewis acids in organic synthesis include dealkylation of ethers, condensation reactions, and as a catalyst for Friedel-Crafts-type reactions and other acid-related chemistry. In general, these are used stoichiometrically in organic transformations under anhydrous conditions, because the presence of even a small amount of water causes rapid decomposition or deactivation of the promoters. To obviate some of these inherent problems, the potential of arylboron compounds, Ar,B(OH),-3 ( n = 1-3), bearing electron-withdrawing aromatic groups as a new class of boron catalysts has recently been demonstrated. For example, tris(pentafluor0phenyl)borane, B(C6F5)3, is a convenient, commercially available Lewis acid of strength comparable with that of BF3, but without the problems associated with reactive B-F bonds. Although its primary commercial application is as a co-catalyst in metallocene-mediated olefin polymerization, its potential as a Lewis acid catalyst for organic transformations is now recognized as being much more extensive. Diarylborinic acids and arylboronic acids bearing electron-withdrawing aromatic groups are also highly effective Lewis acid catalysts.This chapter focuses on the synthetic applications of BX3 as Lewis acids and the organic transformations catalyzed by arylboron...

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Trimethoxyphenylverbindungen, VIII¹⁾ Borheterocyclen in der präparativen Naturstoffchemie; Synthese des Baeckeols²⁾

Cited by 23 publications

References 18 publications

Catalytic Friedel–Crafts Acylation and Benzoylation of Aromatic Compounds Using Activated Hematite as a Novel Heterogeneous Catalyst

Catalytic Friedel–Crafts Acylation and Benzoylation of Aromatic Compounds Using Activated Hematite as a Novel Heterogeneous Catalyst

Simple and Improved Procedure for the Regioselective Acylation of Aromatic Ethers with Carboxylic Acids on the Surface of Graphite in the Presence of Methanesulfonic Acid

Achiral B(III) Lewis Acids

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Trimethoxyphenylverbindungen, VIII1) Borheterocyclen in der präparativen Naturstoffchemie; Synthese des Baeckeols2)

Cited by 23 publications

References 18 publications

Catalytic Friedel–Crafts Acylation and Benzoylation of Aromatic Compounds Using Activated Hematite as a Novel Heterogeneous Catalyst

Catalytic Friedel–Crafts Acylation and Benzoylation of Aromatic Compounds Using Activated Hematite as a Novel Heterogeneous Catalyst

Simple and Improved Procedure for the Regioselective Acylation of Aromatic Ethers with Carboxylic Acids on the Surface of Graphite in the Presence of Methanesulfonic Acid

Achiral B(III) Lewis Acids

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Product

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Trimethoxyphenylverbindungen, VIII¹⁾ Borheterocyclen in der präparativen Naturstoffchemie; Synthese des Baeckeols²⁾