Rearrangement Of Ethers Research Articles

Synthesis and catalytic activity of heterobimetallic Au/M (M = RhIII, IrIII) complexes with ditopic mono- and triphosphane ligands.

A series of heterobimetallic complexes Au/M (M = RhIII, IrIII) were prepared on the basis of two ditopic ligands: a monophosphane ligand L1H and a triphosphane ligand L2H. The complexes were fully characterised, including single-crystal X-ray diffraction studies. Catalytic activity of cationic L1/AuI/IrIII and L2/AuI/IrIII bis(trifluoromethane)sulfonimide was analysed through their capacity to induce allenyl ether rearrangement and cycloisomerisation of N-propargyl benzamide. While cationic L1/AuI/IrIII showed some ability to induce allenyl ether rearrangement, no conversion was observed for cationic L2/AuI/IrIII. Similarly, N-propargyl benzamide could undergo cycloisomerisation in the presence of cationic L1/AuI/IrIII, whereas cationic L2/AuI/IrIII was again inactive. These findings highlight how crucial the surroundings of the metal centre are to the catalytic activity. Catalytic activity is only possible when Au has a free coordination site; the gold complex becomes inactive when the tridentate ligand is present.

Interaction of the transition state of the Claisen rearrangement with surface of carbon nanotubes to predict catalytic activity

The possibility of using the transition state shape selectivity concept for control of selectivity of reaction was previously demonstrated by us using the example of 1,3-dioxanes formation by Prins reaction.The extension of the applied approach to other reactions is of theoretical and practical interest. The aim of our work was to study the interaction of the frozen transition state of Claisen rearrangement with the surface of nanotubes of various structures to predict their catalytic activity.Claisen rearrangement of allylphenyl ether was chosen as a model reaction, and carbon nanotubes with different diameters were chosen as a porous materials. The calculated dependence of the stabilization energy on the nanotube diameter has an extreme character with pronounced maxima at a diameter of 10.2–10.4 Å. The obtained results allow to predict the catalytic activity of nanotubes with a diameter of 10–11 Å in Claisen rearrangement of allylphenyl ether.

3,3]-Sigmatropic rearrangements of propargyl alkynyl ethers. Synthesis of complex dienoates and unsaturated lactones.

In an extension of our studies on low-temperature rearrangements of 1-alkynyl ethers, we describe herein the [3,3]-sigmatropic rearrangement of in situ formed propargyl alkynyl ethers to allenyl ketenes, which furnish complex tert-butyl-(2E,4Z)-dienoates 2 in good yields upon tert-butanol addition. Similarly, sigmatropic rearrangements of in situ formed propargyl lithioalkynyl ethers yield methyl-(2Z,4Z)-dienoates 4 upon methanol addition or unsaturated lactones 6 upon aldehyde or ketone addition to the allenyl ynolate intermediate.

Carpe diene! Europium-catalyzed [3,3] and [5,5] rearrangements of aryl-pentadienyl ethers.

A general protocol for the europium-catalyzed rearrangement of aryl-pentadienyl-ethers is described. The mode of rearrangement and product formation in this reaction was solely determined by the aryl substituent para to the phenol. If the para-position is occupied by a substituent, the substrate undergoes a [3,3] rearrangement to the ortho-position to form a prochiral branched diene. In turn, a free para-position in the starting material allows the reaction to proceed via a [5,5] rearrangement and leads to a linear conjugated diene product. The severely underdeveloped and synthetically valuable [5,5] rearrangement was investigated in terms of scope and mechanism.

Cobalt-catalysed [1,2]-Wittig rearrangement of ethers to secondary alcohols.

Stable ethers are successfully transformed into secondary alcohols via C-O bond activation using a simple cobalt pincer catalyst. Mechanistic studies indicate the involvement of radical pairs, and their sequential recombination and the subsequent hydrolysis results in the formation of secondary alcohols.

Regioselective rearrangement reactions of naphthyl naphthylmethyl ethers by using Lewis acids or UV light irradiation

Reaction of 1-naphthyl naphthylmethyl ethers 1 and 2 with Lewis acids (BF3-Et2O or Et2AlCl) in CH2Cl2 produced rearranged products of the naphthylmethyl group to the 2- and 7-positions of the naphthalene, whereas rearrangement of 2-naphthyl ethers 3 and 4 proceeded to the 1-position. When benzene solution of compound 1 was irradiated, rearrangement to the 4-position proceeded, whereas rearrangement of 2 proceeded to the 2- and 4-positions. Photoinduced rearrangement of 3 and 4 proceeded to the 1-position as in the reaction using Lewis acids. In the reaction with Lewis acids, ion pair consists of Lewis acid-coordinated naphthoxy anions and naphthylmethyl cations, and in the photoreaction, radical pair generated by homolytic cleavage of the C-O bond, are proposed to be intermediates. Calculations of the negative charge distribution and the spin density of the intermediates showed that the regioselectivity of the reactions can be explained by the charge density and spin density of each fragment, steric hindrance, and solvent cage effect.

Unprecedented Rearrangement of β-Difluoroboryloxy Ethers: A Route to C-2 Alkyl-chromenones

AbstractThe addition of boron trifluoride etherate (BF3·OEt2) to allenic ketones has led to the isolation of the isolated boron difluoride enolates. The single-crystal structure of boron enolate has been solved. The unprecedented C1–C10 migration of (Z)-β-difluoroboryloxy ether derivatives is observed to deliver rearranged phenol derivatives which are functionalized to C-2 alkyl-chromenones. Interestingly the isolated boron enolates have exhibited significant anticancer properties.

Mild reductive rearrangement of oximes and oxime ethers to secondary amines with hydrosilanes catalyzed by B(C6F5)3

Oximes, its ether derivatives and the corresponding hydroxylamines rearrange to secondary amines when reacted with PhSiH3 and B(C6F5)3 as catalyst. Computations suggest a reduction–rearrangement to be slightly favored over a Beckmann-type sequence.

Access to N-Alkylpyrazin-2-ones via C–O to C–N Rearrangement of Pyrazinyl Ethers

The reaction of tosylated 2-alkoxypyrazines with potassium halides led to the unexpected formation of N-alkylated pyrazinones. Such rare example of substitutive C–O → C–N rearrangement on pyrazines was then scrutinised by using various nucleophiles to afford the respective products in moderate to good yields. This method provides a direct access to N-alkylated-1H-pyrazin-2-ones. The formation of the rearranged products is conveniently and reliably determined by characteristic NMR shifts of their heteroaromatic protons.

A Lewis‐Acid‐Catalyzed Phenolic Ether ‘O to C’ Rearrangement: Synthesis of 4‐Aryldihydrocoumarins

AbstractAn efficient O to C rearrangement of phenolic ethers is developed. The Lewis acid BF3⋅OEt2 (0.5 equiv) could catalyze the O to C migration of β‐aryloxy‐β‐arylesters to β,β‐bis‐arylesters, thereby the free phenolic OH cyclizes with the ester group, resulting in the formation of 4‐aryldihydrocoumarins.

Asymmetric [2,3]-Wittig Rearrangement: Synthesis of Homoallylic, Allenylic, and Enynyl α-Benzyl Alcohols.

A highly stereoselective [2,3]-Wittig rearrangement of allylic and propargylic ethers controlled by a chiral sulfoxide moiety is presented. The activation provided by the sulfoxide at the remote ortho position allows the rearrangement of less-activated and unexplored benzylic carbanions. Thus, this general methodology gives access to the asymmetric synthesis of homoallylic, enynyl, and allenylic α-benzyl alcohol derivatives.

Attractive Nonbonded Interactions Help Stabilize the Z Form of Alkenyl Anions.

Alkenyl anions ((-)H2C-CH═CH-Y; Y = aliphatic, aromatic, amine, ether) are often thermodynamically stable in the sterically congested Z form. This preference for Z structures is used to control regiochemistry in organometallic and Grignard reactions, allyl amine rearrangements to enamines, and allyl ether rearrangements to enol ethers. Explanations for Z stability in alkenes (Y = CH2R) typically invoke through-space attraction (Coulomb or charge transfer) between the formally anionic carbon C1 and the Y = CH2R hydrogens. However, this explanation is difficult to generalize to amines and ethers. We suggest that the orbital-driven so-called "attractive nonbonded interactions" suggested to stabilize the Z forms of 1,2-difluoroethylene and 1-substituted propenes also help stabilize Z alkenyl anions. We present electronic structure calculations and surveys of the experimental literature to show these effects' relevance for alkenyl anions. Our results suggest new approaches for regiocontrol in reactions with alkenyl anion intermediates and motivate revisiting older orbital-based theories of "attractive nonbonded interactions".

Ruthenium(II) Complexes with η6-Coordinated 3-Phenylpropanol and 2-Phenylethanol as Catalysts for the Tandem Isomerization/Claisen Rearrangement of Diallyl Ethers in Water

A series of half-sandwich ruthenium(II) complexes containing η6-coordinated 2-phenylethanol and 3-phenylpropanol ligands, namely [RuCl2{η6-C6H5CH2(CH2)nCH2OH}(PR3)] (PR3 = PMe3, PPh3, P(OMe)3, P(OEt)3, P(OiPr)3, P(OPh)3; n = 0 (1a–f), 1 (2a–f)), have been investigated as catalysts for the tandem isomerization/Claisen rearrangement of diallyl ethers into γ,δ-unsaturated aldehydes using, for the first time, water as solvent. The best results in terms of activity and regioselectivity were obtained with the 3-phenylpropanol derivative [RuCl2(η6-C6H5CH2CH2CH2OH){P(OEt)3}] (2d). Thus, using only 1 mol % of this complex, in combination with NaOH (2 mol %), different diallyl ethers could be conveniently converted into the corresponding aldehydes in high yields and short times under relatively mild thermal conditions (100 °C).

Cascade Claisen Rearrangement: Rapid Synthesis of Polysubstituted Salicylaldehydes and Total Syntheses of Hemigossypol and Gossypol.

A cascade Claisen rearrangement of a well-organized maltol propargyl ether for the construction of polysubstituted salicylaldehydes is reported. This reaction features high atom economy (100 %), as well as catalyst-free and gram-scale conditions. Based on this novel methodology, the total synthesis of hemigossypol, gossypol, and their analogues has been realized.

Thermal aromatic Claisen rearrangement and Strecker reaction of alkyl(allyl)-aryl ethers under green reaction conditions: Efficient and clean preparation of ortho-allyl phenols (naphthols) and alkyl(allyl)oxyarene-based γ-amino nitriles

Chemical transformations of 13 diverse allyl(alkyl)-aryl ethers, easily prepared using Williamson reaction of different hydroxyarenes and allyl bromide and alkyl (n-butyl, n-octyl) bromides, were studied. Thermal aromatic Claisen rearrangement of allyl-aryl ethers to obtain ortho-allyl phenols (naphthols) employing propylene carbonate as a nontoxic and biodegradable solvent was described for the first time. The use of this green solvent allowed to enhance notably product yields and reduce significantly the reaction time comparing with the use of 1,2-dichlorobenzene, toxic solvent, which is traditionally employed in this type of Claisen rearrangement. Three-component Strecker reaction of selected alkyl(allyl)-aryl ethers with formyl function on aryl fragment, piperidine and potassium cyanide in the presence of sulfuric acid supported on silica gel (SSA, SiO2-O-SO3H) under mild reaction conditions was used in the preparation of new γ-amino nitriles, analogues of alkaloid girgensohnine [2-(4-hydroxyphenyl)-2-(piperidin-1-yl)acetonitrile], a perspective biological model in the search for new insecticidal agrochemicals against Aedes aegypti. The use of SSA, an inexpensive and reusable solid catalyst, allowed to obtain new series of 2-[4-alkyl(allyl)oxyphenyl]-2-(piperidin-1-yl)acetonitriles in short time at room temperature with good yields.

ChemInform Abstract: Synergistic Kinetic Resolution and Asymmetric Propargyl Claisen Rearrangement for the Synthesis of Chiral Allenes.

AbstractThe kinetic resolution of racemic propargyl vinyl ethers (I) through an enantioselective Claisen rearrangement affords chiral allenes (II) and enantiopure ethers (S)‐(I).

GC-ECNICI-MS/MS of eicosanoids as pentafluorobenzyl-trimethylsilyl (TMS) derivatives: Evidence of CAD-induced intramolecular TMS ether-to-ester rearrangement using carboxy-18O-labelled eicosanoids and possible implications in quantitative analysis.

GC-MS and GC-MS/MS of pentafluorobenzyl (PFB) ester trimethylsilyl (TMS) ether (PFB-TMS) derivatives of hydroxylated long-chain fatty acids including arachidonic acid metabolites, the eicosanoids, in the electron-capture negative-ion chemical ionization (ECNICI) mode are the most sensitive and accurate approaches to quantify carboxyl groups-containing compounds in complex biological fluids such as plasma and urine. Under ECNICI conditions, PFB-TMS derivatives of eicosanoids ionize to form very few ions, with the carboxylates [M-PFB]- being typically the most intense. Less intense ions may be additionally formed by consecutive neutral loss (NL) of trimethylsilanol (TMSOH, 90Da) groups ([M-PFB-(TMSOH)n]-). By using [1,1-18O2]- and [1,ω-18O2]-eicosanoids, we studied ion processes following collisionally activated dissociation (CAD) of the precursor ions [M-PFB]-. We found that CAD resulted in formation of product ions due to NL of a TMS18OH (92Da) group in monocarboxylic and of a PFB18OH (200Da) group in dicarboxylic eicosanoids. TMS18OH NL implies an intra-molecular transfer of the TMS group from hydroxyl groups to their carboxylate anions [M-PFB]-. From a mechanistic point of view, this rearrangement may explain formation of unique product ions in GC-MS/MS of eicosanoids under ECNICI conditions. From the quantitative point of view, quantification by GC-MS/MS of product ions due to [M-PFB-(TMSOH)n]- and [M-PFB-TMS18OH-(TMSOH)n-1]-would reveal incorrect data, if [1,1-18O2]-eicosanoids are used as internal standards and if no correction for the 18O-loss is performed. In 18O-labelled dicarboxylic eicosanoids, such as the major urinary metabolite (MUM) of E prostaglandins, i.e., [1,ω-18O2]-PGE-MUM), no TMS ester/TMS ether rearrangement was observed. Yet, 18O-loss occurred upon CAD of [M-PFB]- due to NL of PFB18OH (200Da). In both cases the extent of 18O-loss needs to be determined and considered for accurate quantification of monocarboxylic acids such as 8-isoprostaglandin F2α (8-iso-PGF2α) and dicarboxylic eicosanoids such as PGE-MUM.

Rhodium(II)‐Catalysed Skeletal Rearrangement of Ether Tethered N‐Sulfonyl 1,2,3‐Triazoles: a Rapid Approach to 2‐Aminoindanone and Dihydroisoquinoline Derivatives

AbstractThe skeletal rearrangement of ether tethered N‐sulfonyl‐1,2,3‐triazoles has been achieved by rhodium(II) catalysis. This method offers a rapid entry to 2‐aminoindanone and dihydroisoquinoline architectures which can be further transformed to other valuable building blocks, such as vicinal aminoindanols, isoquinolines and isoquinolinones. A pathway involving an azavinyl rhodium carbene intermediate was proposed according to a preliminary mechanistic study.magnified image

Synergistic Kinetic Resolution and Asymmetric Propargyl Claisen Rearrangement for the Synthesis of Chiral Allenes.

The asymmetric propargyl Claisen rearrangement provides a convenient entry to chiral allene motifs. Herein, we describe the development of a kinetic resolution and asymmetric rearrangement of racemic propargyl vinyl ethers. This transformation afforded chiral allene products along with the enantiomerically enriched substrate in good yields with excellent diastereo- and enantioselectivity. The complete chirality transfer and facially selective rearrangement enabled the simultaneous construction of an axially chiral allenic unit and a quaternary carbon stereocenter.

Synergistic Kinetic Resolution and Asymmetric Propargyl Claisen Rearrangement for the Synthesis of Chiral Allenes

AbstractThe asymmetric propargyl Claisen rearrangement provides a convenient entry to chiral allene motifs. Herein, we describe the development of a kinetic resolution and asymmetric rearrangement of racemic propargyl vinyl ethers. This transformation afforded chiral allene products along with the enantiomerically enriched substrate in good yields with excellent diastereo‐ and enantioselectivity. The complete chirality transfer and facially selective rearrangement enabled the simultaneous construction of an axially chiral allenic unit and a quaternary carbon stereocenter.