Titanocene-catalysed, selective reduction of ketones in aqueous media. A safe, mild, inexpensive procedure for the synthesis of secondary alcohols via radical chemistry

We report here a novel procedure for the reduction of ketones to secondary alcohols using catalytic quantities of commercially available Cp₂TiCl₂, inexpensive Zn dust and water as proton source. Mechanistically the reaction presumably proceeds via titanoxy radicals. In practice this reduction process has significant advantages: it shows an interesting selectivity pattern, takes place under mild conditions using safe, cheap reagents and does not require anhydrous solvents. The proton-donor activity of water under these conditions avoids the use of the frequently poisonous hydrogen-atom donors generally required to reduce free radicals. This procedure is also highly convenient for synthesising deuterium-labelled alcohols employing relatively inexpensive D₂O as deuterium source.     

A Mild and Highly Efficient Method for the Preparation of Silyl Ethers using Fe(HSO4)3/Et3N by Chlorosilanes

A very efficient and mild procedure for preparation of silyl ethers from benzylic, allylic, propargilic alcohols, phenols, naphtoles and some of phenolic drugs with trimethylsilylchloride (TMSCl), triethylsilylchloride (TESCl) and t‐buthyldimethylsilyl chloride (TDSCl) ethers in the presence of Fe(HSO₄)₃/Et₃N in room temperature in excellent yields is reported. This procedure also allows the excellent selectivity for silylation of alcohols and phenols.     

Nickel-catalyzed couplings and cyclizations involving allenes, aldehydes, and organozincs

Cyclizations of allenyl aldehydes and intermolecular couplings of allenes and aldehydes provide a direct procedure for the preparation of homoallylic alcohols. The couplings and cyclizations involve the use of diorganozinc reagents as reducing agents and Ni(COD)₂ as the catalyst.     

Efficient and practical protocol for silylation of hydroxyl groups using reusable lithium perchlorate dispread in silica gel under neutral condition

A very efficient and mild procedure for the trimethylsilylation of a wide variety of alcohols, including primary, allylic, benzylic, secondary, hindered secondary, tertiary, and phenols with hexamethyldisilazane on the surface of silica gel dispersed with LiClO₄ in room temperature at few minutes in excellent yields under neutral conditions is reported. This procedure also allows the excellent selectivity under LP-SiO₂ system for silylation of alcohols in the presence of amine and phenolic hydroxy groups.     

Chemoselective and Catalytic Trimethylsilylation of Alcohols and Phenols by 1,1,1,3,3,3-Hexamethyldisilazane and Catalytic Amounts of PhMe3N+Br3–

 An efficient procedure for the trimethylsilylation of alcohols and phenols is presented. The combination of 1,1,1,3,3,3-hexamethyldisilazane and a catalytic amount of phenyltrimethylammonium tribromide (PhMe3N+Br3?) was found to be effective for the trimethylsilylation of alcohols and phenols. The protection reaction is very simple and homogenously performed in dichloromethane at room temperature and mild conditions.     

Enantioselective reduction of α-substituted ketones mediated by the boronate ester TarB-NO2

A facile and mild reduction procedure is reported for the preparation of chiral secondary alcohols prepared from α-substituted ketones using sodium borohydride and the chiral boronate ester (l)-TarB-NO₂. Direct reduction of substituted ketones bearing Lewis basic heteroatoms generally provided secondary alcohols of only modest enantiomeric excess likely due to either competition between the target carbonyl and the functionalized sidechains at the Lewis acidic boron atom in TarB-NO₂ or the added steric bulk of the α-sidechain. As an alternative method, these substrates were synthesized using TarB-NO₂ via a two-step procedure involving the reduction of an α-halo ketone to a chiral terminal epoxide, followed by regioselective/regiospecific epoxide opening by various nucleophiles. This procedure provides access to a variety of functionalized secondary alcohols including β-hydroxy ethers, thioethers, nitriles, and amines with enantiomeric excesses of 94% and yields up to 98%.     

Efficient and Selective Halogenation of Allylic and Benzylic Alcohols under Mild Conditions

Summary. A simple, mild, and high yielding procedure for the halogenation of allylic and benzylic alcohols using a combination of SOCl₂, benzotriazole, and potassium halides in DMF is described. The effectiveness of the protocol is manifested in its selectivity towards allylic and benzylic alcohols whereas other simple alcohols such as primary, secondary, and tertiary are found to be unreactive.     

A Facile and Efficient Trimethylsilylation of Hydroxyl Groups Using Silica-Supported Zinc Chloride and Alumina-Supported Sodium Hydrogensulfate as Recyclable Heterogeneous Catalysts

Silica-supported zinc chloride (SiO₂-ZnCl₂) and novel alumina-supported sodium hydrogensulfate (NaHSO₄-Al₂O₃) as recyclable heterogeneous catalysts have been used for the mild trimethylsilylation of hydroxyl groups under ambient conditions. This procedure also allows for the selective protection of primary and secondary alcohols in the presence of tertiary alcohols.     

Determination of mono-alcohols by gas chromatography

A gas chromatographic method is described for the determination of alcohols up to C₂₀H₄₁OH. The procedure is rapid and indicates the molecular weight distribution and the contents of straight-chain and branched-chain alcohols. A programmed temperature control with a silicone substrate was satisfactory. n-C₁₄H₂₀OH and n-C₅H₁₁OH were used as internal standards.     

Tris(pentafluorophenyl)borane catalyzed acylation of alcohols,phenols, amines,and thiophenols under solvent-free condition

The acylation of alcohols, phenols, amines, and thiophenols was accomplished with 0.5 mol % of tris(pentafluorophenyl)borane [B(C₆F₅)₃] at ambient temperature under solvent-free condition. Major advantages of this method include high yield, short reaction time, simple procedure, compatibility with sensitive protecting groups as well as other functional groups, absence of racemization of optical active compounds, and epimerization of sugars.     

Iodination of alcohols using triphenylphosphine/iodine under solvent-free conditions using microwave irradiation

A straightforward and effective procedure for the conversion of benzylic, allylic and aliphatic alcohols to the corresponding iodides using Ph₃P/I₂ under solvent-free conditions using microwave irradiation is reported.     

Novel and Efficient One Pot Condensation Reactions between Ketones and Aromatic Alcohols in the Presence of CrO3 Producing α,β‐Unsaturated Carbonyl Compounds

We report a new, effective and simple method for preparing α,β‐unsaturated carbonyl compounds by reacting ketones and aromatic alcohols at 56°C in the presence of CrO₃ (CrO₃ acts as an oxidant and also a catalyst) for around 10 h. The condensation reactions occurred effectively among a wide combination of ketones and alcohols. The procedure is simple and the yields can be high up to 98%. And a probable mechanism is proposed.     

Mild and efficient silylation of alcohols and phenols with HMDS using Bi(OTf)3 under solvent-free condition

A very efficient and mild silylation of alcohols and phenols with hexamethyldisilazane (HMDS) at rt is developed using Bi(OTf)₃ as the catalyst. Primary, secondary and tertiary alcohols as well as phenols are excellently converted into corresponding TMS ethers in a very short reaction time. This procedure can also be applied to large scale silylation for industrial application.     

A highly efficient room temperature non-organometallic route for the synthesis of α,β,β-trifluorostyrenes by dehydrohalogenation

Various 1-aryl-1,2,2,2-tetrafluoroethanes (ArCHFCF₃, Ar=phenyl, substituted phenyl, naphthyl, heteroaryl) were synthesized by the fluorination of the corresponding alcohols with DAST. Dehydrofluorination of ArCHFCF₃ using lithium hexamethyldisilazide (LHMDS) base in THF at room temperature produced 1,2,2-trifluorostyrenes (ArCF=CF₂) in 61-91% isolated yields. This procedure provides an excellent non-organometallic alternative to the generally used metallation-Pd(0) coupling methods.     

Ruthenium‐Catalyzed Tandem‐Isomerization/Asymmetric Transfer Hydrogenation of Allylic Alcohols

A one‐pot procedure for the direct conversion of racemic allylic alcohols to enantiomerically enriched saturated alcohols is presented. The tandem‐isomerization/asymmetric transfer hydrogenation process is efficiently catalyzed by [{Ru(p‐cymene)Cl₂}₂] in combination with the α‐amino acid hydroxyamide ligand 1 , and performed under mild conditions in a mixture of ethanol and THF. The saturated alcohol products are isolated in good to excellent chemical yields and in enantiomeric excess up to 93 %.     

Preparation,characterization and application of RHA/TiO2 nanocomposites in the acetylation of alcohols,phenols and amines

In this work, anatase-phase nano-titania was prepared by embedding in rice husk ash, and identified using a variety of techniques. The obtained nanocomposite (RHA/TiO₂) was used as a green and inexpensive catalyst for the promotion of the acetylation of alcohols, phenols and amines with Ac₂O at room temperature under solvent free conditions. The procedure gave the products in excellent yields during all reaction times. Also this catalyst can be reused for several times without loss of its catalytic activity.     

Significant Heterogeneous Carbonate Salt Catalyzed Acetylation of Alcohols via a Transesterification Process with Carbonate Salt‐activated Alcohol 1H NMR Evidence

Heterogeneous carbonate salt catalyzed acetylation of alcohols via a transesterification process has been developed. Various esters are furnished up to 97% yield. Established procedure is simple and air‐tolerant with readily available reagents. Ethyl acetate and isobutyl acetate are used as not only acetylating agents, but also reaction solvents in transesterification. Aliphatic linear alcohols, allylic alcohols and benzyl alcohols show high reactivities in the presence of 1 or 5 mol% Cs₂CO₃ at 125°C. Cesium carbonate can be recycled by pumping liquid phase out of reactor after reaction. During four cycle runs for reaction of 2‐phenylethanol and ethyl acetate, high yields of phenethyl acetate are provided (>60% yield). Based on experiments and ¹H NMR investigation, bifunctional catalysis is proposed, alcohol activated by carbonate ion is confirmed, and higher activity of catalytic amount than stoichiometric cesium carbonate is interpreted.     

Facile Conversion of Primary and Secondary Alcohols to Alkyl Iodides

A convenient, simple procedure is described for the conversion of a variety of primary and secondary alcohols to iodides in yields ranging from 60–98%. The method employs the Ph₃P/imidazole/I₂ combination of reagents in the solvent dichloromethane.     

Synthesis and characterization of a novel nano-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-copoly[(styrene/acrylic acid)/grafted ethylene oxide and its application as a magnetic and recyclable phase-transfer catalyst in the preparation of β-azido alcohols and β-nitro alcohols

A facile method was developed for the synthesis of β-azido alcohols and β-nitro alcohols in the presence of a novel nano-Fe₃O₄-copoly[(styrene/acrylic acid)/grafted ethylene oxide (nano-Fe₃O₄-PS-Co-[PAA-g-PEG]) as a phase-transfer catalyst in water. The catalyst was characterized with IR, SEM, and TGA. This procedure offers several advantages, including excellent regioselectivity, high yields, short reaction times, a recyclable catalyst, easy separation of the catalyst through an external magnet, and easy workup.     

Stereochemistry of cyclic ether formation—II : Intramolecular cyclisation of secondary aliphatic alcohols to tetrahydrofuran-type ethers

The mechanism and stereochemistry of δ-C atom functionalisation in the reactions of secondary straight-chain aliphatic alcohols with lead tetraacetate, ceric ammonium nitrate, and heavy metal (Pb⁴⁺, Hg²⁺, Ag⁺) salts (AcO)^?1, O^2?, CO₃^2?-halogen (I₂, Br₂, Cl₂) combinations are discussed. By demonstrating the intermediacy of 5-bromo-2-hexanol, it was confirmed that the dark silver oxidebromine induced cyclisation of 2-hexanol (and alcohols in general) involves (as the other hypohalite reactions) intramolecular 1,5-hydrogen abstraction by alkoxy radicals and formation of δ-bromohydrins. A novel and simple procedure for obtaining tetrahydrofurans from alcohols by way of the hypochlorite reaction, using silver or mercuric salts and chlorine, is described.