Primary Benzylic Alcohols Research Articles

Dehydration of Benzyl Alcohols in Phosphonium Ionic Liquids: Synthesis of Ethers and Alkenes

AbstractThe dehydration of benzylic alcohols has been studied in several phosphonium ionic liquids in the absence of any metal catalysts. Benzyl ethers and alkenes were obtained from primary and secondary benzylic alcohols in good to excellent yields for these reactions. Commercially available hydrophobic phosphonium ionic liquids containing the trihexyl(tetradecyl)phosphonium cation paired with six different anions were used for the reactions under microwave irradiation. The interaction of the substrate with the ionic liquid was investigated using different NMR techniques, such as NOESY NMR. The effects of cation and anions on the behaviour of these ionic liquids in the reactions were studied in order to understand the mechanism. A catalytic cycle is proposed involving activation of the benzyl alcohol by the phosphonium cation.

ChemInform Abstract: Activation of Dioxygen by Cobaloxime and Nitric Oxide for Efficient TEMPO‐Catalyzed Oxidation of Alcohols.

The aerobic oxidation of alcohols to their corresponding carbonyl compounds could be efficiently accomplished by using the combination of cobalt nitrate, dimethylglyoxime and 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) as a novel catalytic system, and various alcohols including primary and secondary benzylic, allylic and aliphatic alcohols could be quantitatively converted to the corresponding aldehydes or ketones at 70 °C under 0.4 MPa dioxygen pressure in dichloromethane. During the oxidation, the in situ generated cobaloxime and nitric oxide (NO) were responsible for the activation of dioxygen, respectively, thereby, two concerted catalytic routes exist: cobaloxime-activating-dioxygen TEMPO-catalyzed and NO-activating-dioxygen TEMPO-catalyzed aerobic oxidation of alcohols.

A remarkable effect of ionic liquids in transition-metal-free aerobic oxidation of benzylic alcohols

The transition-metal-free aerobic oxidation of benzylic alcohols is uniquely accelerated by a 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6)/PhCF3 biphasic system and Cs2CO3 to afford the corresponding ketones in good yields. The reaction system is also applicable to an oxidative cross-esterification of primary benzyl alcohols with a higher aliphatic alcohol.

Solid-supported Pd(0): an efficient heterogeneous catalyst for aerobic oxidation of benzyl alcohols into aldehydes and ketones

Solid-supported nano- and microparticles of Pd(0) (SS-Pd) were used as heterogeneous catalysts for aerobic oxidation of benzyl alcohols. Primary and secondary benzyl alcohols gave the corresponding products in good yields. In addition, the catalysts could be reused up to five runs without significant loss of activities.

Novel and chemoselective one-pot synthesis of 4-arylidene-2-phenyl-5(4H)-oxazolones starting from benzyl alcohols promoted by [(C14H24N4)2W10O32]-[bmim]NO3

A new and practical promoter system for one-pot, efficient, chemoselective synthesis of 4-arylidene-2-phenyl-5(4H)-oxazolones using [(C14H24N4)2W10O32]-[bmim]NO3 under solvent-free conditions is described. The present work opens up a new and ecofriendly synthetic route to Erlenmeyer–Plochl adducts from primary benzyl alcohols in a one-pot operation.

Activation of Dioxygen by Cobaloxime and Nitric Oxide for Efficient TEMPO‐Catalyzed Oxidation of Alcohols

AbstractThe aerobic oxidation of alcohols to their corresponding carbonyl compounds could be efficiently accomplished by using the combination of cobalt nitrate, dimethylglyoxime and 2,2,6,6‐tetramethylpiperidine 1‐oxyl (TEMPO) as a novel catalytic system, and various alcohols including primary and secondary benzylic, allylic and aliphatic alcohols could be quantitatively converted to the corresponding aldehydes or ketones at 70 °C under 0.4 MPa dioxygen pressure in dichloromethane. During the oxidation, the in situ generated cobaloxime and nitric oxide (NO) were responsible for the activation of dioxygen, respectively, thereby, two concerted catalytic routes exist: cobaloxime‐activating‐dioxygen TEMPO‐catalyzed and NO‐activating‐dioxygen TEMPO‐catalyzed aerobic oxidation of alcohols.

ChemInform Abstract: Yttrium Triflate Catalyzed Efficient Chemoselective S‐Benzylation of Indoline‐2‐thiones Using Benzyl Alcohols.

A highly efficient yttrium triflate-catalyzed chemoselective S-benzylation of indolin-2-thiones using variously substituted benzyl alcohols has been developed for the synthesis of indole-based sulfides. This procedure presents a greener approach for the synthesis of S-alkylated indoles. The reaction condition is amenable to primary, secondary, and tertiary benzylic alcohols as the benzyl group donors.

Synthesis and Characterization of the Transition Metal Complexes: Their Alcohol Oxidation and Electrochemical Properties

Five Schiff base ligands, HA1, HA2, H2L1-H2L3, and their Co(II), Mn(III) and Ru(III) complexes, have been synthesized and characterized by analytical, spectroscopic, conductance, magnetic moment, and electrochemical studies. The oxidation of benzylic alcohols to the corresponding carbonyl compounds is described. In the case of some primary benzyl alcohols, high conversions were obtained. Secondary benzyl alcohol (2-hydroxy–1,2-diphenylethanone derivatives) were selectively transformed to the corresponding ketone with satisfactory conversions. The electrochemical properties of all complexes have been recorded in the different scan rates and solvents. The electrochemical properties of the complexes change with scan rates.

ChemInform Abstract: A Green and Efficient Oxidation of Benzylic Alcohols Using H2O2 Catalyzed by Montmorillonite‐K10 Supported MnCl2.

AbstractPrimary and secondary benzylic alcohols are oxidized to the corresponding carbonyl compounds in good yields with the help of the title catalyst, which is found to be reusable at least three times without a significant decrease in its activity.

AlBr3·6H2O catalyzed oxidation of benzylic alcohols

AlBr3·6H2O was found to be an efficient catalyst in the field of oxidation of benzylic alcohols. Primary and secondary benzylic alcohols could be transformed into corresponding aldehydes and ketones with almost complete conversion and high selectivity. The non-transition metal related reaction systems have an incomparable advantage over others, such as easy work-up, excellent selectivity as well as commercial availability.

Readily Accessible Oxazolidine Nitroxyl Radicals: Bifunctional Cocatalysts for Simplified Copper Based Aerobic Oxidation

AbstractUsing a two‐step procedure a range of bifunctional oxazolidine nitroxyl radicals have been prepared. The application of these co‐catalysts to the copper‐based aerobic oxidation of alcohols was then investigated. From these studies it was found that the parent tetramethyloxazolidine nitroxyl radical L1 was competent for oxidation in the presence of 2,2′‐bipyridine, and the bifunctional pyridyl‐containing nitroxyl radicals L2 and L3 could be used in the absence of additional coordinating ligands. Following optimization, the scope of this simplified transformation was explored, demonstrating that a range of primary and secondary benzylic alcohols are readily oxidized. In addition, the oxidation of allylic alcohols and hydroquinone can be achieved.

Yttrium triflate-catalyzed efficient chemoselective S-benzylation of indoline-2-thiones using benzyl alcohols

A highly efficient yttrium triflate-catalyzed chemoselective S-benzylation of indolin-2-thiones using variously substituted benzyl alcohols has been developed for the synthesis of indole-based sulfides. This procedure presents a greener approach for the synthesis of S-alkylated indoles. The reaction condition is amenable to primary, secondary, and tertiary benzylic alcohols as the benzyl group donors.

ChemInform Abstract: Regioselective Synthesis of Phthalans via Cu(OTf)2‐Catalyzed 5‐exo‐Dig Intramolecular Hydroalkoxylation of 2‐(Ethynyl)benzyl Alcohols.

Abstract An efficient, regioselective Cu(OTf)2-catalyzed 5-exo-dig intramolecular hydroalkoxylation of 2-(ethynyl)benzyl alcohol, which provides a concise access to functionalized phthalan in high yields has been developed. A wide range of substrates possessing terminal, internal, and heteroaromatic alkynes can be efficiently transformed into the targeted phthalans. Substrates with primary, secondary, and tertiary benzyl alcohols also proceed well to produce the corresponding phthalans in good yields. Irrespective of the nature of the substrates, the cyclization follows highly selective 5-exo-dig regiochemistry when regioselectivity is an issue.

Efficient and Selective Aerobic Alcohol Oxidation Catalyzed by Copper(II)/2,2,6,6,‐Tetramethylpiperidine‐1‐oxyl at Room Temperature

AbstractA simple and efficient copper(II)/2,2,6,6,‐tetramethylpiperidine‐1‐oxyl (TEMPO)‐catalyzed aerobic oxidation of both primary and secondary benzylic, allylic, and aliphatic alcohols to their corresponding aldehydes and ketones at room temperature using the copper(II) complex [Cu(μ‐Cl)(Cl)(phen)]2 as the Cu(II) source is reported. The conversion of both electron‐rich and electron‐neutral benzyl alcohols is smooth and faster than those of electron‐deficient ones. The chemoselectivity of a primary benzyl alcohol over the secondary alcohol is also observed. Alcohols regarded as difficult substrates for oxidation due to their coordinating ability with transition metal catalyst such as 4‐(methylthio)benzyl alcohol and 3‐pyridinemethanol are also oxidized easily. In addition, a lignin model alcohol is oxidized to the corresponding aldehyde in excellent yield. Conversions of benzylic and allylic alcohols are faster as compared to those of aliphatic alcohols in accordance with their CαH bond strengths. A plausible mechanism of the TEMPO‐based catalytic cycle is proposed.

Oxidation of primary and secondary alcohols by 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate in aqueous media

The water soluble oxidant 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate 1 oxidizes primary and secondary aliphatic, primary allylic, and primary and secondary benzylic alcohols to their corresponding aldehydes and ketones in aqueous media in good to excellent yields.

Catalytic Activity and Regeneration Property of a Pd Nanoparticle Encapsulated in a Hollow Porous Carbon Sphere for Aerobic Alcohol Oxidation

A core-shell composite consisting of a palladium (Pd) nanoparticle and a hollow carbon shell (Pd@hmC) was employed as a catalyst for aerobic oxidation of various alcohols. The core-shell structure was synthesized by consecutive coatings of Pd nanoparticles with siliceous and carbon layers followed by removal of the intermediate siliceous layer. Structural characterizations using TEM and N(2) adsorption-desorption measurements revealed that Pd@hmC thus-obtained was composed of a Pd nanoparticle core of 3-6 nm in diameter and a hollow carbon shell with well-developed mesopore (ca. 2.5 nm in diameter) and micropore (ca. 0.4-0.8 nm in diameter) systems. When compared to some Pd-supported carbons, Pd@hmC showed a high level of catalytic activity for oxidation of benzyl alcohol into benzaldehyde using atmospheric pressure of O(2) as an oxidant. The Pd@hmC composite also exhibited a high level of catalytic activity for aerobic oxidations of other primary benzylic and allylic alcohols into corresponding aldehydes. The presence of a well-developed pore system in the lateral carbon shell enabled efficient diffusion of both substrates and products to reach the central Pd nanoparticles, leading to such high catalytic activities. This core-shell structure also provided high thermal stability of Pd nanoparticles toward coalescence and/or aggregation due to the physical isolation of each Pd nanoparticle from neighboring particles by the carbon shell: this specific property of Pd@hmC resulted in possible regeneration of catalytic activity for these aerobic oxidations by a high-temperature heat treatment of the sample recovered after catalytic reactions.

One‐Pot Synthesis of Symmetrical 1,3‐Diarylureas or Substituted Benzamides Directly from Benzylic Primary Alcohols and Effective Oxidation of Secondary Alcohols to Ketones Using Phenyliodine Diacetate in Combination with Sodium Azide

AbstractBenzylic primary alcohols can be directly converted into symmetrical 1,3‐diarylureas or substituted benzamides via an one‐pot oxidative reaction using the combined reagent of phenyliodine diacetate and sodium azide. This new reaction constitutes a step‐economical way to prepare symmetric 1,3‐diarylureas or substituted benzamides depending upon the substituents on the phenyl rings of starting alcohols. The sodium acetate generated in situ from the ligand exchange between phenyliodine diacetate and sodium azide plays the pivotal role in the formation of 1,3‐diarylureas. In addition, it is also found that various secondary alcohols can be readily oxidized to their corresponding ketones in excellent yields using the same reagent system of phenyliodine diacetate and sodium azide. Generally, secondary alcohols are preferentially oxidized to the corresponding ketones in the presence of primary ones with the limited amounts of phenyliodine diacetate and sodium azide.

Oxidation of alcohols mediated by a polymer supported potassium ferrate as an effective mild oxidant

AbstractThe use of polymeric oxidizing agents simplifies routine oxidation of reactions because it eliminates the traditional purification. In this article, the use of the cross‐linked poly (4‐vinylpyridine)‐supported potassium ferrate as an effective mild polymeric oxidizing agent is described. This reagent is capable of oxidizing organic compounds and can be used as a versatile reagent in organic synthesis. Primary and secondary benzylic and allylic alcohols are converted selectively to their carbonyl compounds, and hydroquinone to the 1, 4‐benzoquinone. This polymeric reagent seems to be nontoxic and nonpollutant. Based on our observation during the study, the polymeric reagent is stable and can be stored for months without losing its activity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

A green and efficient oxidation of benzylic alcohols using H 2O 2 catalyzed by Montmorillonite-K10 supported MnCl 2

Primary and secondary benzylic alcohols were oxidized to the corresponding carbonyl compounds in good to high yields by environmentally friendly and green oxidant, H 2O 2 catalyzed by Montmorillonite-K10 supported manganese(II) chloride.

Regioselective synthesis of phthalans via Cu(OTf) 2-catalyzed 5- exo- dig intramolecular hydroalkoxylation of 2-(ethynyl)benzyl alcohols

An efficient, regioselective Cu(OTf) 2-catalyzed 5- exo- dig intramolecular hydroalkoxylation of 2-(ethynyl)benzyl alcohol, which provides a concise access to functionalized phthalan in high yields has been developed. A wide range of substrates possessing terminal, internal, and heteroaromatic alkynes can be efficiently transformed into the targeted phthalans. Substrates with primary, secondary, and tertiary benzyl alcohols also proceed well to produce the corresponding phthalans in good yields. Irrespective of the nature of the substrates, the cyclization follows highly selective 5- exo- dig regiochemistry when regioselectivity is an issue.