Benzyl ethers group protection

Selective hydrogenolysis of the benzyl ether group was performed in the presence of an N-Boc protecting group. In this case, 10 Pd/C (0.45 mol/mol) and HC02NH4 (6.5 mol/mol) was warmed at reflux in acetone for 30 minutes (Scheme 4.55).258... 

Notes This is often used as a protecting group for alcohols, where it is observed that primary alcohols form more readily than secondary hydroxy groups, which in turn are more reactive than tertiary alcohols. As with most benzylic ethers, this protecting group can be removed by hydrogenolysis over Pd or by metal-ammonia reduction.1 Examples ... 

The typical reactions of the alcohol group include their conversion to ethers and esters by reaction with alkyl halides and with acid chlorides or anhydrides, respectively (Scheme 6.2). The benzyl ether group is readily cleaved by hydrogenolysis and is often used as a protecting group for alcohols. Primary alcohols are oxidized initially to the aldehyde and then to the carboxylic acid. 

General problems, as compared to the formation of 0-glycosides, are the incompatibility between catalytic hydrogenolysis and sulfur functions, which complicates the use of benzyl ethers as protecting groups, although Birch reduction might be an alternative, and the easy formation of disulfides from thiols, irrespective of if they are used as donors or acceptors. 

For a rational synthesis of 1,2-diethers as syn or arUi isomers using benzyl ether groups as protective groups see K. Iwamoto, H. Shimizu, K. AraM and S. Shinkai, J. Am. Chem. Soc., 115, 3997 (1993). 

In this way hydroxyl groups can be protected during synthetic work by conversion into benzyl ether groups and can be regenerated later under mild conditions. 

Nucleosides are formed from benzyl ethers of ribose or deoxyribose by replacement of the acetal benzyl groups by bromide and coupling with the mercury salts of nucleic bases. The benzyl ether groups are removed by treatment with ammonia (Fischer-Helferich method not shown). In the case of pyrimidine nucleosides, one usually converts the lactams first to aromatic di-trimethylsilane ethers, which then react in high yields with protected halogenoses (Scheme 8.5.4)... 

The combination of TMSOTf and EtsN in dichloromethane (DCM) allows the direct conversion of p-methoxybenzyl ethers into silyl-protected alcohols, thus affording an expedient way to replace the benzyl ether-type protective group with the sUyl ether-type one (eq 35). ... 

So far, methods are available for saturated monoacylphosphoglycerides. These are discussed by Slotboom and Bonsen (1970). For production of a 1-monoacyl compound, the 2 position of glycerol can be protected with a benzyl ether group. Slotboom et al. (1963, 1967) prepared rac-l-stearoyl lysophos-... 

Apart from the acyl function, the protection of hydroxyl groups has also been carried out by etherification. The benzyl ether group has been the group of choice, because it can be cleaved either by acidolysis or by catalytic hydrogenation. Protection of the hydroxyl group by methylation... 

In order to avoid the degradation of the dendrimer, a benzyl ether group was used as the protecting group to obtain the carborane synthon shown in Scheme 27.6. In addition, the core of the... 

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