The mechanism of phenol methylation on acid and basic zeolite catalysts

The alkylation of phenol with methanol on HY and CsY/CsOH catalysts was studied in situ under static conditions by ¹³C NMR spectroscopy. Attention was largely given to the identification of intermediate compounds and mechanisms of anisole, cresol, and xylenol formation. The mechanisms of phenol methylation were found to be different on acid and basic catalysts. The primary process on acid catalysts was the dehydration of methanol to dimethyl ether and methoxy groups. This resulted in the formation of anisole and dimethyl ether, the ratio between which depended on the reagent ratio, which was evidence of similar mechanisms of their formation. Subsequent reactions with phenol gave cresols and anisoles. Cresols formed at higher temperatures both in the direct alkylation of phenol and in the rearrangement of anisole. The main alkylation product on basic catalysts was anisole formed in the interaction of phenolate anions with methanol; no cresol formation was observed. The deactivation of acid catalysts was caused by the formation of condensed aromatic hydrocarbons that blocked zeolite pores. The deactivation of basic catalysts resulted from the condensation of phenol and formaldehyde with the formation of phenol-formaldehyde resins.     

Ethers on Si(001): A Prime Example for the Common Ground between Surface Science and Molecular Organic Chemistry

By using computational chemistry it has been shown that the adsorption of ether molecules on Si(001) under ultrahigh vacuum conditions can be understood with classical concepts of organic chemistry. Detailed analysis of the two‐step reaction mechanism—1) formation of a dative bond between the ether oxygen atom and a Lewis acidic surface atom and 2) nucleophilic attack of a nearby Lewis basic surface atom—shows that it mirrors acid‐catalyzed ether cleavage in solution. The O−Si dative bond is the strongest of its kind, and the reactivity in step 2 defies the Bell–Evans–Polanyi principle. Electron rearrangement during C−O bond cleavage has been visualized with a newly developed method for analyzing bonding, which shows that the mechanism of nucleophilic substitutions on semiconductor surfaces is identical to molecular S_N2 reactions. Our findings illustrate how surface science and molecular chemistry can mutually benefit from each other and unexpected insight can be gained.     

Rearrangement of Aryl Geranyl Ethers

This article describes the thermal rearrangement reactions of aryl geranyl ethers. These reactions depend on the structure of the aryl moiety of the substrate and the reaction conditions used. The naphthyl ethers underwent a [1,3]-alkyl shift, followed by acid-catalyzed intramolecular cyclization. The microwave-assisted rearrangement of isoquinolinyl ether showed a pattern of an abnormal Claisen rearrangement. The multi step rearrangement of the quinolyl ether afforded a spiro compound. These new reactions were used to synthesize novel heterocyclic compounds.     

Selective catalytic activity of ball-shaped Pd@MCM-48 nanocatalysts

Remarkable selectivity is achieved in the cleavage of benzyl ethers using ball-shaped palladium nanocatalysts, Pd@MCM-48, in an MCM-48 matrix. The unique nanocatalysts not only feature unprecedented complete hydrogenolysis selectivity of a benzyl ether over hydrogenation of a double bond, but also demonstrate selective cleavage of unsubstituted benzyl ether over substituted benzyl ethers.     

ELECTRON-TRANSFER REACTIONS OF CROSSLINKED POLY(1-PYRIDINIOMETHYL)STYRENE CHLORIDE 2. REDUCTION OF NITRO-COMPOUNDS

Continuing the study of electron transfer reactions of polypyridiniomethylstyrene chloride (PSPyCl), the reduction of nitro-compounds by the PSPyCl-Zn system was investigated. In general azoxy compounds were obtained as chief intermediate product of reduction. Reduction of nitrobenzo-15-crown-5 and its homologues give a new class of bis-crown ether compounds——azoxy-bisbenzocrown ethers. Azoxybisbenzocrown ethers undergo photoinduced trans-cis isomerization, which is reversible on irradiation with UV and on storage in darkness, similar to the case of azobiscrown ethers. Investigation of solvent extraction of various cations by azobiscrown ether isomers shows that cis-azoxybisbenzo-15-crown-5 exhibit good selectivity toward Nd~(3 ) from other rare earth cations.     

Hydrogen migrations in mass spectrometry. I—The loss of olefin from phenyl-n-propyl ether following electron impact ionization and chemical ionization

Using specifically labelled compounds we have made a detailed study of the source of the hydrogen transferred in the elimination of C₃H₆ from the molecular ion of phenyln-propyl ether following electron impact ionization and from the protonated (and ethylated) molecule following chemical ionization. The migrating hydrogen originates from all three positions of the npropyl group but not in the ratio expected for randomization of the alkyl hydrogens prior to transfer. The source of the migrating hydrogen is similar for both electron impact ionization and chemical ionization, indicating that the factors governing the rearrangement are the same for both modes of ionization. From a comparison of the results for labelled 2,6-dimethyl phenyl n-propyl ethers with the results for the unsubstituted ether it is concluded that hydrogen transfer occurs only to the ether oxygen and not to the phenyl ring. A two-step mechanism involving a set of competing reversible hydrogen transfer reactions followed by C? O bond cleavage is proposed to explain the results.     

Decomposition of vinyl ethers by alkalide K, K(15-crown-5)2 via organopotassium intermediates

The structure of vinyl ethers determines the direction of the C-O bond cleavage by alkalide K⁻, K⁺(15-crown-5)₂1. Highly reactive organopotassium compounds are intermediate products formed in the system containing phenyl vinyl ether, butyl vinyl ether, ethylene glycol butyl vinyl ether or triethylene glycol methyl vinyl ether. Vinylpotassium and butylpotassium react with 15-crown-5. The oxacyclic ring of the latter is opened in this case. Organopotassium ethers possessing CH₂CH₂O units eliminate ethylene. It results in various potassium alkoxides. The reaction of 1 with butyl vinyl ether occurs very slow as compared to other vinyl ethers and most of other reagents used till now.     

Acyl Iodides in Organic Synthesis: VI. Reactions with Vinyl Ethers

Reactions of acetyl iodide with butyl vinyl ether, 1,2-divinyloxyethane, phenyl vinyl ether, 1,4-di-vinyloxybenzene, and divinyl ether were studied. Vinyl ethers derived from aliphatic alcohols (butyl vinyl ether and 1,2-divinyloxyethane) react with acetyl iodide in a way similar to ethyl vinyl ether, i.e., with cleavage of both O–Csp2 and Alk–O ether bonds. From butyl vinyl ether, a mixture of vinyl iodide, butyl acetate, vinyl acetate, and butyl iodide is formed, while 1,2-divinyloxyethane gives rise to vinyl iodide, vinyl acetate, and 2-iodoethyl acetate. The reaction of acetyl iodide with divinyl ether involves cleavage of only one O–Csp2 bond, yielding vinyl acetate and vinyl iodide. In the reactions of acetyl iodide with phenyl vinyl ether and 1,4-divinyloxybenzene, only the O–CVin bond is cleaved, whereas the O–CAr bond remains intact.     

Catalytic Reduction of Cyclic Ethers with Hydrosilanes

Catalytic reductive transformations of ethers as a synthetic building block are an important class of chemical reactions because a range of essential chemical feedstocks and fuels in contemporary life can be prepared through the key step of ethereal C?O bond cleavage of cellulosic biomass. Although conventional stoichiometric and catalytic methods for sp²‐ and sp³‐C?O bond cleavage of linear ethers and alcohols with hydrosilanes are well established, silylative ring opening of cyclic ethers has been less highlighted in this context. This review outlines catalytic systems for the silylative reduction of a range of cyclic ethers, including epoxides and sugars, leading to the corresponding alcohols and/or hydrocarbons. The chemical reactivity and selectivity of these ring‐opening catalytic processes are discussed with respect to the type of substrates; the representative catalytic working modes are also described.     

Pyrolysis of arylglycol-β-propylphenyl ether lignin model in the presence of borosilicate glass fibers. : I. Pyrolysis reactions of β-ether compounds

Two β-aryl ether type model compounds, guaiacylglycol- and veratrylglycol-β-propylphenyl ethers, were copyrolyzed with borosilicate glass fibers. The results provided a better understanding of the effect of copyrolysis with the fibers on the yields of lignin-derived products from lignocellulosics.

The observed products indicated the following reactions occurring in the models; (1) cleavage of the C-aromatic ring bond, (2) cleavage of the β-ether bond, (3) cleavage of the C-Cβ bond, (4) ,β-dehydration, and (5) demethylation, and others. Of these reactions, reactions (1), (2) and (4) were the main pyrolysis reactions and fully explained the increase in the total yield of lignin-derived pyrolysis products from Japanese red pine (Pinus densiflora Sieb. et Zucc.) in the presence of borosilicate glass fibers. Reaction (1) was a particularly characteristic reaction in copyrolysis with the fibers. Important reactions relating to the increase in the total yield of lignin-derived pyrolysis products were reproduced on the models used.     

Isomerization and Cleavage of Allyl Ethers of Carbohydrates by Trans- [Pd(NH3)2Cl2

Allyl ethers are widely used for the “temporary” protection of hydroxy groups in carbohydrates. The allyl group is conveniently removed by isomerization and subsequent cleavage of the labile prop-1-enyl group.² The rearrangement of allyl ethers to prop-1-enyl ethers is readily achieved by treatment with potassium t-butoxide in dimethyl sulfoxide, using tris(tripheny1phosphine)rhodium chloride, palladium on activated charcoal and by an ene reaction with diethylazodicarboxylate. acidic conditions, ozonolysis followed by alkaline hydrolysis, reaction with alkaline permanganate solution, or treatment with mercuric chloride in the presence of mercuric oxide. The isomerization of allyl ethers to prop-1-enyl ethers can also be carried out in the presence of palladium on carbon or complex bis(benzonitrile)palladium(11) chloride. Bruce and Roshan-Ali' showed that derivatives of allyl phenyl ether are smoothly cleaved by this complex. This has made it possible to remove the protecting group in a one-pot operation. We have now investigated the effect of palladium catalysts on the isomerization and cleavage of the allyl group in carbohydrate derivatives.     

Novel Selectivity in Carbohydrate Reactions III. Selective Deprotection of p-Methoxybenzyl (PMBn) Ethers of Carbohydrates by Tin(IV)Chloride 1

In multi-step syntheses involving polyhydroxylated natural products such as carbohydrates that are variously derivatized at different positions, orthogonal removal of one or another type of protecting group is of vital importance. Discrimination of different classes of protecting groups, such as ethers, esters, etc., is often possible with a great degree of success, as for example, selective removal of an 0-acetyl by catalytic transesterification in the presence of an ether protecting group, or hydrogenolytic removal of a benzyl ether protection in the presence of ester groups such as acetates.³ Differentiation of different types of protecting groups within a given class of protecting groups has also been similarly achieved with great success, as for example, hydrogenolytic removal of a benzyl ether group in the presence of a methyl ether.³ However, the situation becomes more challenging when the same protecting group is used to mask more than one position in a polyfunctional molecule and their preferential partial deprotection is required. Selective unmaslung of one or more of such protecting groups has been achieved in some cases.4 Of particular interest to us was the regioselective deprotection of the 2-0-benzyl group of per- 0-benzylated 1,6-anhydromannopyranose mediated by SnC14 (1) and Tic14 (2). Considering the greater susceptibility of p-methoxybenzyl (PMBn) ethers to Lewis acid catalysts5 and the complexation of benzyl ethers with 14b and 24b16 we decided to investigate the action of 1 on PMBn ethers of some carbohydrates, We expected the methoxy substituent on the phenyl group in the PMBn moiety to enhance complexation with 1, possibly resulting in a facile reaction under mild conditions. Since 1 is a strong Lewis acid, the need to use chlorotrimethylsilane and anisole, as in the tin(I1)chloride- chlorotrimethylsilane-anisole system for deprotection of PMBn ethers, can be eliminated. Moreover, the complex formation in the case of 1 presents possibilities for unusual regioselectivity in partial de-0-p-methoxybenzylation reactions, a problem that has not been addressed in reports on the oxidative cleavage of PMBn ethers by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)⁷ ceric ammonium nitrate (CAN),⁸ N-bromosuccinimide (NBS)⁸ or bromine⁸.

     

Ring cleavage of THP and THF ethers using dimethylboron bromide

The reaction of dimethylboron bromide with THP and THF ethers was studied. Under conditions of kinetic control, these reactions proceed by selective cleavage of the ring carbon—oxygen bond to give acyclic α-bromo ethers. Treatment of these intermediates with a variety of nucleophiles gives ring-opened products.     

饱和漆酚双冠醚的电子电离质谱

本文总结了饱和漆酚双冠醚电子电离质谱的裂解规律。十个测试样品的结构均为二个芳香冠醚通过NHCORCONH对称桥连而成。当R为烷基时,裂解首先发生在酰胺键或其邻近的键上。R为芳基时则在分子的冠醚部份首先发生裂解。文中还叙述了在某些化合物中的特殊的氢重排反应。     

Cleavage of the ethereal bond : XI. The reaction of allylic organomagnesium halides with 1,3-benzoxathiole and 1,3-benzodioxole

Some reactions of 1,3-benzoxathiole and 1,3-benzodioxole with allylic Grignard reagents have been examined and found to give cleavage of the ether bond to form substitution products with almost complete allylic rearrangement.     

Polylactones. 16. Cationic Polymerization of Trimethylene Carbonate and Other Cyclic Carbonates

1,3-Dioxanone-2 (trimethylene carbonate) was polymerized by use of methyl triflate or triethyloxonium fluoborate under various reaction conditions. Chloroform, 1,2-dichloroethane, and nitrobenzene were used as solvents; the temperature was varied between 25 and 50°C; and the monomer/initiator ratio between 50 and 400. However, inherent viscosities above 0.29 dL/g ( M _n > 6000) were never obtained, owing to side reactions such as backbiting and formation of ether groups. IR and ¹H-NMR spectroscopy revealed that the polymerization mechanism agrees with that of the cationic polymerization of lactones in that propagation involves cleavage of the alkyl-oxygen bond. The active cationic chain end and the dead methylcarbonate end groups were identified by means of ¹H-NMR spectra. A reaction mechanism for the formation of ether groups is discussed. Furthermore, ¹H-NMR spectroscopy indicated that ethylene carbonate and biphenyl-2,2′-carbonate do not react with methyl triflate at 20, 60, or even 100°C.     

Reaktionsverhalten von 1-Fluorsilyl-2,2,4,4,6,6-hexamethylcyclotrisilazanen gegenüber lithiierten Aminen

Reactions of 1-Fluorosilyl-2,2,4,4,6,6-hexamethylcyclotrisilazanes with Lithio-amines Fluorosilylsubstituted hexamethylcyclotrisilazanes show three different typs of reactions with lithiated amines: (a) substitution, (b) ring coupling and (c) ether cleavage reactions. With increasing size of the alkyl or aryl groups respectively of the lithiated amines substitution is superseded by ring coupling. Bulky secundary amines, like lithium-di-iso-propylamine under the same conditions lead to ether cleavage and substitution of an ethoxi group. A system in which a six and a five membered Si? N ring are connected via a Si? n bond bond from the reaction of trifluorosilylhexamethylcyclotrisilazane with di-lithio-N,N′-dimethylethylenediamine. The mass, ¹H- and ¹⁹F-n.m.r. spectra of the compounds are reported.     

Vinyl polymerization versus [1,3] O to C rearrangement in the ruthenium-catalyzed reactions of vinyl ethers with hydrosilanes

Two reactions, vinyl polymerization and [1,3] O to C rearrangement of vinyl ethers, are investigated in the ruthenium-catalyzed reaction with hydrosilanes. The reaction pathways are dependent on the substituents of the vinyl ether, in particular, those of the alkoxy group. Primary-, secondary-, and tertiary-alkyl vinyl ethers, ROCHCH₂, are polymerized with ease to give the corresponding polymer in good yields. When R is electron-donating benzyl groups, the reaction does not give the polyvinyl ether but results in [1,3] O to C rearrangement to give the corresponding aldehyde, RCH₂CHO in moderate to good yields. The rearrangement selectively proceeds when vinyl ethers having α-substituents are used as the starting materials to give the corresponding ketones in high yields. With catalytic amounts of hydrosilanes, the rearrangement gives ketones or aldehydes selectively. In sharp contrast, use of excess amounts of hydrosilanes leads to the rearrangement followed by reduction of the formed carbonyl group to give the corresponding silyl ethers in good yields. Nature of catalytically active species is discussed.     

Interaction of polyfluoroaromatic compounds with o-aminophenol. The Smiles rearrangement in the polyfluoroaromatic series

The reactions of polyfluoroaromatic compounds containing an electron-attracting substituent other than fluorine in the aromatic ring with o-aminophenol proceed at the amino or hydroxy group and lead to the corresponding hydroxydiarylamines (in neutral media) or aminodiaryl ethers (in alkaline media). The latter compounds, unlike 2,3,4,5,6-pentafluoro- 2'-aminodiphenyl ether, are transformed in dimethylformamide (DMFA) to isomeric polyfluoro-2-hydroxydiarylamines (the Smiles rearrangement). The increased electron-attracting capacity of substituent leads to the decreased activation energy and increased rearrangement rate constants.     

Tandem dual C(sp3)-H/C(sp2)-H functionalization: a radical cyclization of 2-isocyanobiphenyl with ether to 6-alkylated phenanthridine

<正>1 General experimental details 1H NMR and 13 C NMR spectra were measured on 400 MHz spectrometer, using CDCl3 as the solvent with tetramethylsilane(TMS) as the internal standard at room temperature. Chemical shifts(δ) are given in ppm relative to TMS, the coupling constants J are given in Hz. HRMS were recorded on a TOF LC/MS equipped with electrospray ionization(ESI) probe operating in positive or negative ion mode.