Allylation Of Phenols Research Articles

Enantio- and Regioconvergent Nickel-Catalyzed Etherification of Phenols by Allylation to Access Chiral C(sp3)-O Allyl Aryl Ethers.

An enantio- and regioconvergent allylation of phenols under nickel catalysis with an α-/γ-regioisomeric mixture of racemic silylated/germylated allylic chlorides is reported. The silyl/germyl group governs the regioselectivity, and the transformation affords enantiomerically enriched unsymmetrical 1,3-disubstituted allyl aryl ethers with excellent regiocontrol in good yields and excellent enantioselectivities. Notably, no nickel-mediated C-O bond activation is observed at room temperature. The synthetic value of these densely functionalized silicon-containing building blocks is demonstrated in a series of chemoselective transformations, including a [3,3]-sigmatropic rearrangement for the construction of an α-chiral silane.

Enantio‐ and Regioconvergent Nickel‐Catalyzed Etherification of Phenols by Allylation to Access Chiral C(sp3)–O Allyl Aryl Ethers

An enantio‐ and regioconvergent allylation of phenols under nickel catalysis with an α‐/γ‐regioisomeric mixture of racemic silylated/germylated allylic chlorides is reported. The silyl/germyl group governs the regioselectivity, and the transformation affords enantiomerically enriched unsymmetrical 1,3‐disubstituted allyl aryl ethers with great regiocontrol in good yields and with excellent enantioselectivities. Notably, no nickel‐mediated C–O bond activation is observed at room temperature. The synthetic value of these densely functionalized silicon‐containing building blocks is demonstrated in a series of chemoselective transformations, including a [3,3]‐sigmatropic rearrangement for the construction of an α‐chiral silane.

Sustainability and efficiency assessment of vanillin allylation: in solution versus ball-milling

Allylation of phenols, a widely used reaction in multistep synthetic pathways, was herein investigated using mechanochemistry and compared to more conventional synthesis in solution.

Palladium-catalyzed decarboxylative O-allylation of phenols with γ-methylidene-δ-valerolactones

A novel palladium-catalyzed decarboxylative O-allylation of phenols was developed, in which a GMDV was found to be an efficient and selective allylation reagent, affording the target allyl phenyl ethers in up to 92% yields.

Nickel/Brønsted acid dual-catalyzed regioselective C–H bond allylation of phenols with 1,3-dienes

A nickel/Brønsted acid dual-catalyzed C-H bond ortho-allylation of phenols with 1,3-dienes has been developed. This methodology is readily applicable to the modification of complex pharmaceutical molecules.

Regiospecific and site-selective C–H allylation of phenols with vinyldiazo compounds catalyzed by In(iii)

An In(OTf)3-catalyzed regiospecific, site-selective, and C–H chemoselective insertion reaction of phenols with vinyldiazoacetates was developed. The reactions of aryl or alkyl substituted vinyldiazoacetates exhibited different selective manners.

Pd]-Catalyzed para-selective allylation of phenols: access to 4-[(E)-3-aryl/alkylprop-2-enyl]phenols.

4-[(E)-3-Arylprop-2-enyl]phenols are omnipresent scaffolds and constitute natural products and biologically significant compounds. Obtusastyrene and obtustyrene are two such phenolic-based natural products isolated from Dalbergia retusa. The development of strategies based on a site-selective allylation, particularly protecting group-free substrates and non-activated coupling agents, is indispensable in organic synthesis. Herein, we present a highly regioselective [Pd]-catalyzed para-allylation of phenols using simple, inactivated allylic alcohols as allylating coupling partners. Notably, this strategy is successful in open-air and under mild reaction conditions. Besides, the efficacy of the present protocol was demonstrated by the direct synthesis of obtusastyrene and obtustyrene.

Catalytic, Enantioselective, Intramolecular Sulfenofunctionalization of Alkenes with Phenols.

The catalytic, enantioselective, cyclization of phenols with electrophilic sulfenophthalimides onto isolated or conjugated alkenes affords 2,3-disubstituted benzopyrans and benzoxepins. The reaction is catalyzed by a BINAM-based phosphoramide Lewis base catalyst which assists in the highly enantioselective formation of a thiiranium ion intermediate. The influence of nucleophile electron density, alkene substitution pattern, tether length and Lewis base functional groups on the rate, enantio- and site-selectivity for the cyclization is investigated. The reaction is not affected by the presence of substituents on the phenol ring. In contrast, substitutions around the alkene strongly affect the reaction outcome. Sequential lengthening of the tether results in decreased reactivity, which necessitated increased temperatures for reaction to occur. Sterically bulky aryl groups on the sulfenyl moiety prevented erosion of enantiomeric composition at these elevated temperatures. Alcohols and carboxylic acids preferentially captured thiiranium ions in competition with phenolic hydroxyl groups. An improved method for the selective C(2) allylation of phenols is also described.

Regio- and Stereospecific C- and O-Allylation of Phenols via π-Allyl Pd Complexes Derived from Allylic Ester Carbonates.

Two complementary strategies have been developed for the C- and O-allylation of phenols via a common π-allyl Pd complex. While O-allylation of phenols by this method is a well-recognized reaction of general utility, the associated para-selective C-allylation reaction is still in its infancy. Cationic π-allyl Pd intermediates, derived from allylic ester carbonates and palladium(0) catalyst, were found to undergo the Friedel-Crafts-type para-selective C-allylations with nine different phenols. Both C- and O-allylated products were obtained in good to excellent yields following a metal-catalyzed regio- and stereospecific substitutive 1,3-transposition. Conditions were also identified that control access to either allylated product. Finally, a study of the equilibrium established between the two allylation products revealed that the O-allylated compound was the kinetic product and the C-allylated compound the thermodynamic product.

Rhodium-Catalyzed Dynamic Kinetic Asymmetric Allylation of Phenols and 2-Hydroxypyridines.

Inspired by the mechanistic studies of rhodium-catalyzed atom-economic addition of carboxylate acids to allenes, a rhodium-catalyzed dynamic kinetic asymmetric allylation of different nucleophiles with racemic allylic carbonates has been developed. High regio- and enantioselectivities can be obtained under neutral conditions and, furthermore, the chemoselectivities can be controlled by different diphosphine ligands. (R,R)-QuinoxP* leads to selective O-allylation of phenols, whereas when embedding (S,S)-DIOP as the ligand, 2-naphthol is ortho-C-allylated for the first time in high enantioselectivity. To this end, hydroxypyridines can be N-allylated by Rh(I) /(S)-DTBM-Segphos via the same intermediate as in the previously reported atom-economic addition to allenes.

ChemInform Abstract: Regio‐ and Enantioselective Allylation of Phenols via Decarboxylative Allylic Etherification of Allyl Aryl Carbonates Catalyzed by (Cyclopentadienyl)ruthenium(II) Complexes and Pyridine‐Hydrazone Ligands.

(Cyclopentadienyl)tris(acetonitrile)ruthenium hexafluorophosphate [CpRu(CH3CN)3][PF6] in combination with pyridine-hydrazone ligands efficiently catalyzes the asymmetric decarboxylative allylic rearrangement of allyl aryl carbonates. Formation of C[BOND]O bonds with high regio- and enantioselectivity ratios (up to 95:5 and 98% ee) is obtained. Good stereocontrol of the pseudotetrahedral geometry of the CpRu moiety is achieved by the hydrazone ligand and its “electron-poor” nature is evidenced through the epimerization of the hexacoordinated TRISPHAT-N anion.

Regio‐ and Enantioselective Allylation of Phenols via Decarboxylative Allylic Etherification of Allyl Aryl Carbonates Catalyzed by (Cyclopentadienyl)ruthenium(II) Complexes and Pyridine‐Hydrazone Ligands

Abstract(Cyclopentadienyl)tris(acetonitrile)ruthenium hexafluorophosphate [CpRu(CH3CN)3][PF6] in combination with pyridine‐hydrazone ligands efficiently catalyzes the asymmetric decarboxylative allylic rearrangement of allyl aryl carbonates. Formation of CO bonds with high regio‐ and enantioselectivity ratios (up to 95:5 and 98% ee) is obtained. Good stereocontrol of the pseudotetrahedral geometry of the CpRu moiety is achieved by the hydrazone ligand and its “electron‐poor” nature is evidenced through the epimerization of the hexacoordinated TRISPHAT‐N anion.magnified image

Synthesis and structure of [Ru(PPh3)2(bipy)(MeCN)Cl][BPh4] and it's catalytic property towards regioselective and stereoselective allylation of phenols

The compound, [Ru(PPh3)2(bipy)(MeCN)Cl][BPh4] (1) has been synthesized from the precursor complex, [Ru(bipy)(PPh3)2Cl2]. The complex has been structurally characterized. This complex has been found to be an efficient catalyst for the regioselective allylation of phenols.

Preparation of chiral ruthenium(iv) complexes and applications in regio- and enantioselective allylation of phenols

Facile preparations of chiral [Ru(Cp*)]- and [Ru(Cp')]-based allyl complexes featuring N,O chelate derived from (+)-nopinone are described. Single crystal X-ray structural analysis of one complex revealed the preferential configuration of the ruthenium centre and the orientation of the unsymmetrical allylic substituent. Applications of these complexes in catalysis for nucleophilic allylic substitution allowed regio- and enantioselective formation of branched allyl ethers from phenols.

Regioselective Iron-Catalyzed Decarboxylative Allylic Etherification

An anionic iron complex catalyzes the decarboxylative allylation of phenols to form allylic ethers in high yield. The allylation is regioselective rather than regiospecific. This suggests that the allylation proceeds through pi-allyl iron intermediates in contrast to related allylations of carbon nucleophiles that have been proposed to proceed via sigma-allyl complexes. Ultimately, iron catalysts have the potential to replace more expensive palladium catalysts that are typically utilized for decarboxylative couplings.

Cationic Ruthenium‐Cyclopentadienyl‐Diphosphine Complexes as Catalysts for the Allylation of Phenols with Allyl Alcohol; Relation between Structure and Catalytic Performance in O‐ vs. C‐Allylation

AbstractA new catalytic method has been investigated to obtain either O‐ or C‐allylated phenolic products using allyl alcohol or diallyl ether as the allyl donor. With the use of new cationic ruthenium(II) complexes as catalyst, both reactions can be performed with good selectivity. Active cationic Ru(II) complexes, having cyclopentadienyl and bidentate phosphine ligands are generated from the corresponding Ru(II) chloride complexes with a silver salt. The structures of three novel (diphosphine)Ru(II)CpCl catalyst precursor complexes are reported. It appears that the structure of the bidentate ligand has a major influence on catalytic activity as well as chemoselectivity. In addition, a strong cocatalytic effect of small amounts of acid is revealed. Model experiments are described that have been used to build a reaction network that explains the origin and evolution in time of both O‐allylated and C‐allylated phenolic products. Some mechanistic implications of the observed structure vs. performance relation of the [(diphosphine)RuCp]+ complexes and the cocatalytic role of added protons are discussed.

Synthesis of cyclotriveratrylene dendrimers and their supramolecular complexes with fullerene C60

Dendrimers with cyclotriveratrylene core and polybenzyl ether branches were synthetised by a convergent Fréchet approach. The cyclotriveratrylene was obtained by trimerisation of phenolic allyl ether of vanillyl alcohol and its structure was characterised by X-ray diffraction. The synthesised dendrimers of first and second generations were used to obtain the supramolecular complexes with fullerene C60. The ability of the fullerene C60 to form supramolecular complexes with the cyclotriveratrylene dendrimers was confirmed by 1H and 13C NMR studies. The value of the association constant K a = 678 ± 60 mol− 1 dm3 calculated on the basis of UV–vis spectroscopic measurements for the titration of the fullerene C60 solution in toluene with increasing amount of the cyclotriveratrylene dendrimer suggest that the fullerene resides mainly near the central core. All the compounds were characterised by 1H, 13C NMR, FTIR, UV–vis spectroscopy, MALDI-TOF, FAB+ mass spectra and elemental analysis.

Kinetics of allylation of phenol using quaternary ammonium membranes in a membrane reactor

Anion exchange membranes were prepared in the laboratory by polymerizing chloromethylstyrene with the crosslinking reagent divinylbenzene, coated on polypropylene nonwoven fabric using the paste method, and then immobilized with trimethyl and tributyl amine in a quaternarization process. The properties of these membranes were characterized in terms of ion-exchange capacity and SEM image. The kinetics of allylation of phenol was also investigated in an organic and alkaline aqueous solution in a vertical membrane reactor. The operating conditions, such as reaction temperature, kind of membrane (two laboratory- and one commercially prepared), and concentration ratio of reactants were established to achieve the optimum condition.

Kinetics of Synthesizing Polymer-Supported Quaternary Ammonium Catalysts

This study attempted to synthesize the optimum quaterary ammonium poly(styrene-co-methylstyrene) catalyst using the combinatorial chemistry method. The catalyst was synthesized by a mix-split method. A phase-transfer catalyst library with 25 kinds of polystyrene-supported quaternary ammonium salt catalyst was the the result of the reaction of five kinds of chloromethylated crosslinked polystyrene with five tert-amines. The allylation of phenol and the oxidation of benzyl alcohol were used as the probing reaction to screen out the most active catalyst for the reaction using the iterative deconvolution method. The screening conditions included teritary amine and organic solvent. The structure of the most active catalyst in the allylation of phenol shows 20 mol % ring substitution and 0.177-0.25-mm pellet size activated with trihexylamine. For oxidation of benzyl alcohol, the reaction conditions of the most active catalyst included a resin of 20% ring substitution and pellet size of 0.177-0.25 mm, activated with triethylamine reacting in an organic solvent of n-hexane.

Catalytic kinetics of quaternary ammonium poly(styrene‐co‐methylstyrene) resin

AbstractThe catalytic kinetics and synthesis of poly(styrene‐co‐chloromethylstyrene) resin of different degrees of crosslinkages and ring substitutions were investigated by copolymerizing styrene and chloromethylstyrene through crosslinking with divinylbenzene. Poly(styrene‐co‐chloromethylstyrene) quaternary ammonium salt was obtained with activating poly(styrene‐co‐chloromethylstyrene) resin with tertiary amine. More than 20 types of poly(styrene‐co‐chloromethylstyrene) quaternary ammonium catalyst were prepared, with reaction conditions including immobilized time (0.125∼4 days), concentration of tertiary amine (0.1∼2 kmol/m3), kinds of solvents in immobilization (methanol, ethyl alcohol, and DMF), and kinds of tertiary amines (trimethylamine, triethylamine, tripropylamine, tri‐n‐butylamine, tri‐n‐pentylamine, tri‐n‐hexylamine, and tri‐n‐octylamine). These catalysts were used to achieve the optimum allylation of phenol. The reactions were conducted and studied individually with either equal mole or equal weight of catalyst. The best reactivity for the allylation of phenol was obtained when the structure of the quaternary ammonium catalyst was 10% degree of ring substitution and 2% degree of crosslinkage activating with trihexylamine. The turnover number and the effectiveness factor were also calculated. © 2006 American Institute of Chemical Engineers AIChE J, 2006