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Benzyl Group

Benzoyl chloride is a favored source of benzoyl groups, being used to prepare benzoyl ketones, benzamides (benzoyl amides), and benzoate esters. The source of many naturally occurring benzoyl compounds is the thioester benzoyl-CoA. Irradiation of benzil generates benzoyl radicals, which have the formula PhCO.

benzyl group

Benzoyl esters and amides are common in organic chemistry. The esters are used as a protecting groups in organic synthesis,[4] which can be easily removed by hydrolysis in dilute basic solution. Benzoyl-β-D-glucoside is a natural substance that can be found in Pteris ensiformis.

Benzyl groups are occasionally employed as protecting groups in organic synthesis. Their installation and especially their removal require relatively harsh conditions, so benzyl is not typically preferred for protection.[9]

where R is the gas constant (8.314 J/mol K); T is the absolute temperature (K); n is equal to 1 for single chain ionic surfactants displaying only one ionisable group; and dγ/d log C can be calculated from the slope of the straight section before the CMC in the plot of surface tension versus concentration of the surfactant.

A comparison between MICs of leucine-based quaternary ammonium surfactants with and without (values are reported in [14]) the N-benzyl group may indicate the contribution of this substituent to the antimicrobial activity. Overall, the antimicrobial activity is negatively affected by the introduction of the N-benzyl group, as is evident for the C12 and C14 derivatives. Conversely, an enhanced effect by the presence of the benzyl group was observed in the case of the C10 derivative against the two Gram-positive bacterial species Staphylococcus aureus and Enterococcus faecalis (Figure 5).

Comparison between MIC values from leucine-based quaternary ammonium surfactants (C10, C12 and C14) without or in the presence of the benzyl group. The MIC ratio is calculated from the ratio of MIC values for leucine surfactants without and with the benzyl group. MICs for surfactants without the benzyl group are from [14].

In terms of adsorption properties and lowering of surface tension, the substitution of a methyl group with a benzyl group exerts a double effect by increasing the hydrophobicity and the steric hindrance of the ammonium quaternary polar head. Indeed, leucine-based surfactants in the presence of the N-benzyl group have CMC values lower than the corresponding N-methylated compounds due to the higher hydrophobicity. Moreover, only C10 N-benzyl surfactants maintained γCMC values around 30 mN/m, similarly to all N-methylated compounds, while, for the C12 and C14 N-benzyl derivatives, the γCMC values increased up to 40 mN/m, probably due to the combined effect of a larger size of the polar head and the longer hydrophobic tail.

Cytotoxicity studies with these materials were performed on two cell lines relevant to the oral (Caco-2) and respiratory (Calu-3) route of administration. The data showed a clear link between the EC50 values and CMC, similarly to N-methylated compounds and other classes of surfactants [6,24,25]. Slightly lower EC50 values were calculated for the C12 and C14 derivatives of N-benzyl surfactants, while, for the C10 derivatives, these values were comparable to the counterpart N-methylated compound. A clear relationship between EC50 and the other surface parameters (Γmax and Amin) was not found, suggesting that CMC is the most sensitive physicochemical property affecting cytotoxicity.

The following are available online at -4923/11/6/287/s1, Table S1: Chemical structures and H1-NMR interpretation for benzyl quaternary ammonium leucine-based surfactants. Table S2: Selectivity index (EC50/MIC) for the synthesised leucine-based quaternary ammonium surfactants in comparison to BAC. EC50 values are from the MTS assay.

A protocol for the anti-Markovnikov hydrofunctionalization of alkenes has been developed by the use of a benzyl group as a traceless redox-active hydrogen donor. Under copper catalysis and in the presence of CF3 - or N3 -containing hypervalent iodine reagents, a series of homoallylic alcohol derivatives were hydrofunctionalized regioselectivity. A similar principle was also applied to the hydrofunctionalization of alkenols.

New homoscorpionate ligands containing a 3-benzyl substituent, hydrotris(3-benzyl-5-methylpyrazol-1-yl)borate, Tp(Bn,Me), and hydrotris(3-benzyl-4-phenylpyrazol-1-yl)borate, Tp(Bn,4Ph), have been synthesized, and the dynamic behavior of a number of metal complexes was studied by NMR. Structures of the complexes Tl[Tp(Bn,Me)], 1, Tl[Tp(Bn,4Ph)], 2, Co[Tp(Bn,Me)][Tp(Np)], 3, Mo[Tp(Bn,Me)](CO)(2)NO, 4, Co[Tp(Bn,4Ph)][Tp], 5, and Mo[Tp(Bn,Me)](CO)(2)(eta(3)-methallyl), 6, were determined by X-ray crystallography. In the Tp(Bn,Me) ligand, the benzyl group is freely rotating and provides less steric hindrance to the coordinated metal than a neopentyl group, but steric hindrance is increased in the Tp(Bn,4Ph) ligand, where the rotation of the benzyl substituent is restricted by the 4-phenyl substituent.

Benzyl ethers can by generated using theWilliamson Ether Synthesis, for example, where initial deprotonation of the alcohol and subsequent reaction with benzyl bromide delivers the protected alcohol. Use of NaH as base for the deprotonation is convenient, but when selective substitution is needed - for example, protection of one hydroxyl group in diols or selective protection of a more accessible group - mild bases such as Ag2O allow a more selective reaction. For substrates that are not stable to basic conditions, the use of benzyl trichloroacetimidate allows protection under acidic conditions. As an example of a new benzylating reagent, 2-Benzyloxy-1-methylpyridinium triflate allows protection even under neutral conditions (see recent literature).

Deprotection is normally performed as palladium-catalyzed hydrogenation, delivering the alcohol and toluene. In the presence of other reducible groups, a hydrogen transfer source such as 1,4-cyclohexadiene can be used to limit the availability of hydrogen.

Cleavage of benzyl ethers is also possible using strong acids, but this method is limited to acid-insensitive substrates. Alternatively, oxidation to the benzoate allows a subsequent hydrolysis under basic conditions. Some substituted benzyl ethers enable more specific, high yielding deprotection methods. For example: p-methoxybenzyl ethers can also be cleaved using single electron oxidants such as DDQ, because the attached methoxy group stabilizes intermediates better due to resonance. Recently, a more reliable method for the use of DDQ with simple benzyl ethers has been reported using photoirradiation.

Another substituted version, the 2-nitrobenzyl group, has shown utility as a photoremovable protecting group, particularly in biochemical systems where chemical removal is impractical or impossible. This group can be removed by irradiation at 308 nm, and proceeds via oxidation of the benzylic position. (P. Kociensky, Protecting Groups, 3rd Edition, Thieme Verlag, Stuttgart 2006, 252.)

Inexpensive stable crystalline 2,4,6-tris(benzyloxy)-1,3,5-triazine (TriBOT) can be used as an acid-catalyzed O-benzylating reagent. The reaction of various functionalized alcohols with 0.4 equiv of TriBOT in the presence of trifluoromethanesulfonic acid afforded benzyl ethers in good yields. TriBOT, which is the formal trimerization of the smallest unit of benzyl imidate, offers high atom economy.K. Yamada, H. Fujita, M. Kunishima, Org. Lett., 2012,14, 5026-5029.

A fast, quantitative benzylation of hindered sugar hydroxyls with NaH/THF is possible in the presence of a catalytic amount of the quaternary ammonium salt IN(Bu)4. A sample procedure with catalyst produces quantitative yield after 10 - 165 min at r.t. versus 24 h at reflux with excess benzyl bromide and no catalyst.S. Czernecki, C. Georgoulis, C. Provelenghiou, Tetrahedron Lett., 1976,17, 3535-3536.

2-Benzyloxy-1-methylpyridinium triflate is a stable, neutral organic salt that converts alcohols into benzyl ethers upon warming. Benzylation of a wide range of alcohols occurs in very good yield.K. W. C. Poon, G. B. Dudley, J. Org. Chem., 2006,71, 3923-3927.

A bench-stable chiral 9-hydroxy-9,10-boroxarophenanthrene catalyst is applied in a highly enantioselective desymmetrization of 2-aryl-1,3-diols using benzylic electrophiles under operationally simple, ambient conditions. Nucleophilic activation and discrimination of the enantiotopic hydroxy groups on the diol substrate occurs via a defined chairlike six-membered anionic complex.C. D. Estrada, H. T. Ang, K.-M. Vetter, A. A. Ponich, D. G. Hall, J. Am. Chem. Soc., 2021, 143, 4162-4167.

A catalytic amount of Pd(η3-C3H5)Cp and DPEphos as ligand efficiently converted aryl benzyl carbonates into benzyl-protected phenols through a decarboxylative etherification. Alternatively, the nucleophilic substitution of benzyl methyl carbonates with phenols proceeded in the presence of the catalyst, yielding aryl benzyl ethers.R. Kuwano, H. Kusano, Org. Lett., 2008,10, 1795-1798.

Facile reductive etherification of carbonyl compounds can be conveniently performed by reaction with triethylsilane and alkoxytrimethylsilane catalyzed by iron(III) chloride. The corresponding alkyl ethers, including benzyl and allyl ethers, of the reduced alcohols were obtained in good to excellent yields under mild reaction conditions.K. Iwanami, H. Seo, Y. Tobita, T. Oriyama, Synthesis, 2005, 183-186.

A regioselective reductive ring opening of benzylidene acetals in carbohydrate derivatives using triethylsilane and molecular iodine is fast and compatible with most of the functional groups encountered in oligosaccharide synthesis, and offers excellent yields. The reaction conditions are equally effective in thioglycosides.R. Panchadhayee, A. K. Misra, Synlett, 2010, 1193-1196. 041b061a72

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