Iron-catalyzed cross etherification of alcohols to form unsymmetrical benzyl ethers

Eco-Friendly Homo- and Cross-Etherification of Benzyl Alcohols Catalyzed by Iron(II/III) Chloride in Propylene Carbonate as a Green and Recyclable Solvent

A new catalytic approach toward the symmetrical and nonsymmetrical etherification of benzyl alcohols was developed. The symmetrical etherification reaction was carried out in the presence of FeCl3·6H2O (5 mol %) as the catalyst and propylene carbonate as a green and recyclable solvent and led to the corresponding symmetrical ethers in 53 to 91% yields. The nonsymmetrical etherification of benzylic alcohols was achieved by using FeCl2·4H2O (10 mol %) in the presence of a pyridine bis-thiazoline ligand (12 mol %) and allowed for high selectivity and in 52 to 89% yields. These methods take advantage of eco-friendly conditions.

The Bis(indolylmethyl) ethers: Design, Prototypical Synthesis, and Scope Studies

The design, prototypical synthesis, isolation, and characterization of bis(indolylmethyl) ethers from corresponding indolylcarbinols is described. This approach involves very mild conditions and exhibits good scope for indolylcarbinols (both N-electron withdrawing group and N-electron donating group). Cross etherification between two electronically different indolylcarbinols is also demonstrated for the generation of unsymmetrical ethers. For the first time, the intermediacy of the bis(indolylmethyl) ethers for the formation of bis(indolyl)methanes from indolylcarbinols is proved experimentally and by 1H NMR analysis.

Iridium-catalyzed reductive etherification of α,β-unsaturated ketones and aldehydes with alcohols

An iridium complex-catalyzed reductive etherification of α,β-unsaturated ketones and aldehydes with primary alcohols is presented, affording allyl ethers in excellent yields. Deuterated and control experiments showed that this etherification transformation proceeded through a cascade transfer hydrogenation and alcohol condensation process. Moreover, the utility of this protocol is evidenced by the gram-scale performance.

Hydrogen-bond donor and acceptor cooperative catalysis strategy for cyclic dehydration of diols to access O-heterocycles

Dehydrative cyclization of diols to O-heterocycles is attractive, but acid and/or metal-based catalysts are generally required. Here, we present a hydrogen-bond donor and acceptor cooperative catalysis strategy for the synthesis of O-heterocycles from diols in ionic liquids [ILs; e.g., 1-hydroxyethyl-3-methyl imidazolium trifluoromethanesulfonate ([HO-EtMIm][OTf])] under metal-free, acid-free, and mild conditions. [HO-EtMIm][OTf] is tolerant to a wide diol scope, shows performance even better than H₂SO₄, and affords a series of O-heterocycles including tetrahydrofurans, tetrahydropyrans, morpholines, dioxanes, and thioxane in high yields. Mechanism investigation indicates that the IL cation and anion serve as hydrogen-bond donor and acceptor, respectively, to activate the C─O and O─H bonds of alcohol via hydrogen bonds, which synergistically catalyze dehydrative cyclization of diols to O-heterocycles. Notably, the products could be spontaneously separated after reaction because of their immiscibility with the IL, and the IL could be recycled. This green strategy has great potential for application in industry.

Zirconium-catalysed direct substitution of alcohols: enhancing the selectivity by kinetic analysis

Kinetic analysis was used as a tool for rational optimization of catalytic direct substitution of alcohols to enable selective formation of ethers, thioethers, and Friedel–Crafts alkylation products using a moisture-tolerant and commercially available Zr complex.

Development of a Storable Triazinone-Based Reagent for O- p-Methoxybenzylation under Mild Heating Conditions

A new triazinone-based reagent for O- p-methoxybenzylation has been developed. In spite of its stability in solid form, this reagent converts a free alcohol into the corresponding p-methoxybenzyl ether with mild heating (50-60 °C) in a solution. High functional group tolerance can be achieved because the reaction does not require the addition of an acidic or basic activator.

Cp*CoIII -Catalyzed Efficient Dehydrogenation of Secondary Alcohols

A novel, well-defined molecular Cp*Co^III complex was isolated and structurally characterized for the first time. The efficiency of this cobalt catalyst was demonstrated in the alcohol dehydrogenation and dehydrative coupling of secondary alcohols under mild conditions into ketones and ethers, respectively.

Iron-Catalyzed Selective Etherification and Transetherification Reactions Using Alcohols

Simple and readily available iron(III) triflate turned out to be a cheap, environmentally benign, and efficient catalyst for the direct etherification of alcohols. The use of ammonium chloride as an additive (5 mol %, 1 equiv relative to catalyst) suppressed the side reactions completely and ensured the selective ether formation even on challenging substrates containing electron-donating substituents. This method allows the selective synthesis of symmetrical ethers from benzylic secondary alcohols and unsymmetrical ethers directly from secondary and primary alcohols. Moreover, transetherification of symmetrical ethers using primary alcohols is attained. The reaction progress of symmetrical ether and unsymmetrical ether formation followed zero-order and first-order kinetics, respectively. Electron paramagnetic resonance (EPR) measurements of the reaction mixture and simple iron(III) triflate clearly indicated that oxidation state of the metal center remains same throughout the catalysis. Mechanistic studies confirmed that the unsymmetrical ether formation occurs via the in situ formed symmetrical ethers.

B(C6F5)3 catalyzed direct nucleophilic substitution of benzylic alcohols: an effective method of constructing C–O, C–S and C–C bonds from benzylic alcohols

An efficient and general method of nucleophilic substitution of benzylic alcohols catalyzed by non-metallic Lewis acid B(C₆F₅)₃ was developed. The reaction could be carried out under mild conditions and more than 35 examples of ethers, thioethers and triarylmethanes were constructed in high yields. Some bioactive organic molecules were synthesized directly using the methods.

An efficient and general method of nucleophilic substitution of benzylic alcohols catalyzed by non-metallic Lewis acid B(C₆F₅)₃ was developed.