Coupling benzylic alcohols

Complexation of [Cp IrCl2]2 with iV-heterocyclic carbenes has led to complexes such as 25, developed by Peris and coworkers [107, 108], and 133, developed by Crabtree and coworkers [12]. Complex 24 is activated by the addition of silver triflate and is effective for the iV-alkylation of amines with alcohols and for the iV-alkylation of anilines with primary amines. Complex 25 has also been shown to couple benzyl alcohol 15 with a range of alcohols, including ethanol 134, to give ether products such as ether 135 (Scheme 31). Complex 133 was an active hydrogen transfer catalyst for the reduction of ketones and imines, using 2-propanol as the hydrogen source. It was also an effective catalyst for the iV-alkylation of amines... 

The addition of larger amounts of amylamine does not lead to an increase in the quantity of organics adsorbed to the particle surface. However, when higher amounts of dodecylamine were added to the dispersion, a continuous rise in the amount of bound stabilizer is observed. This points to a higher affinity of the long-chain stabilizer to the particle surface and results in different molar stabilizer-to-particle ratios required to stabilize 100 % of the particles in the system. In detail, the first weight-loss step is attributed to fragile bound volatile solvents the second step is related to the bonnd stabilizer and the third step reflects the desorption of coupled benzyl alcohol from the particle surface [17]. 

Carbocations can also be generated during the electrolysis, and they give rise to alcohols and alkenes. The carbocations are presumably formed by an oxidation of the radical at the electrode before it reacts or diffuses into solution. For example, an investigation of the electrolysis of phenylacetic acid in methanol has led to the identification of benzyl methyl ether (30%), toluene (1%), benzaldehyde dimethylacetal (1%), methyl phenylacetate (6%), and benzyl alcohol (5%), in addition to the coupling product bibenzyl (26%). ... 

Allylic or benzylic alcohols can be symmetrically coupled by treatment with... 

Related to these strategies, Fe(OTf)3/TfOH cocatalyzed the coupling reaction of terminal alkynes with benzylic alcohols in the absence of base by means of a sp-sp C-C bond formation (Scheme 16) [32]. 

Dehydration reactions catalysed by NHC complexes have been reported where a new C-C bond is formed. Peris has used [Ir(OTf)2Cp (NHC)] complexes including compound 35 to benzylate arenes with alcohols and other reagents [14]. For example, the dehydrative C-C coupling of benzyl alcohol 8 with toluene 33 is catalysed by 0.1 mol% of 35 to give a mixture of benzylated products 34 (Scheme 11.8). 

In addition to the reductive coupling reaction of ketones, certain alcohols can also be reductively coupled using active uranium. Benzhydrol is coupled by active uranium to give TPA as the only coupled product. No TPE is seen. Under similar conditions, no coupling of benzyl alcohol is seen. The chemistry of the active uranium is under continued investigation. 

Organolithium reagent 35 was added to aldehyde 31 (Scheme 7.6) to obtain alcohol 36 as an inconsequential 1 1 mixture of diastereomers. The benzylic alcohol was removed using a Barton two-step radical deoxygenation protocol, followed by electrophilic aromatic bromination to provide the desired coupling partner 37. 

Chaudhuri et al. (216) reported that the dinuclear bis(phenoxyl)dicopper(II) species [Cu2(Ls )2]Cl2 (Fig- 30) reacts under anaerobic conditions in dry THF in a stoichiometric fashion with primary and secondary alcohols (ethanol, benzyl alcohol, 2-propanol, diphenylcarbinol, and 2-butanol) with formation of two different products, namely, aldehydes (or ketones) and 1,2-diols (and/or other oxidative C— C coupling products). 

Chromium(II) sulfate is a versatile reagent for the mild reduction of a variety of bonds. Thus aqueous dimethylformamide solutions of this reagent at room temperature couple benzylic halides, reduce aliphatic monohalides to alkanes, convert vicinal dihalides to olefins, convert geminal halides to carben-oids, reduce acetylenes to /raw5-olefins, and reduce a,j3-unsatu-rated esters, acids, and nitriles to the corresponding saturated derivatives. These conditions also reduce aldehydes to alcohols. The reduction of diethyl fumarate described in this preparation illustrates the mildness of the reaction conditions for the reduction of acetylenes and o ,j8-unsaturated esters, acids, and nitriles. 

A number of compounds react rapidly with DDQ at room temperature. They include allylic and benzylic alcohols, which can thus be selectively oxidized, and enols and phenols, which undergo coupling reactions or dehydrogenation, depending on their structure. Rapid reaction with DDQ is also often observed in compounds containing activated tertiary hydrogen atoms. The workup described here can be used in all these cases. 

A mixture of titanium trichloride and 0.33 equivalent of lithium aluminum hydride in dimethoxyethane causes coupling of the benzyl residues benzyl alcohol thus affords bibenzyl in 78% yield [204],... 

Consistent with the results of this study is the outcome of the oxidation of 4-X-substituted phenols by use of PINO, generated from HPI with Pb(OAc)4 at 25 °C in MeCN containing 1% AcOH . The reactivity (fcn) of PINO towards phenolic O—H bonds (BDE 85-90 kcal moC ) was about one order of magnitude higher than that measured towards the C—H bond of benzyl alcohols (cf. Table 4). A p value of —3.1 was obtained from plotting log kn vs. for this reaction, where removal of H-atom from the phenolic O—H bond (which is weaker than the O—H bond of aliphatic or benzyl alcohols) induces an oxidative phenolic coupling with the PINO moiety. In view of the low redox potential of the substituted phenols (in the 0.8-1.1 V/NHE range), and of the substantial value of the kinetic isotope effect = 3.1-3.7 measured, ... 

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