Benzyl Protective Groups
Benzyl groups are frequently used in organic synthesis as protective group for alcohols and carboxylic acids.
Two common methods for benzyl ether protection:
- reaction of alcohol with benzyl bromide and a strong base such as sodium hydride as in a Williamson ether synthesis
- reaction of alcohol with an imidate such as benzyl trichloroacetimidate (C6H5CH2OC(CCl3)=NH) promoted by trifluoromethanesulfonic acid. An example forming a p-methoxybenzyl (PMB) ether in total synthesis:
The benzyl group can be removed by hydrogenation. PMB ethers can be cleaved by magnesium bromide –dimethyl sulfide, CAN or DDQ.
One study employs a benzyloxy pyridinium salt as a benzyl transfer reagent for alcohols:
Trifluorotoluene was used as the solvent in the presence of magnesium oxide as an acid scavenger. The reaction type for this conversion is believed to be SN1 based on the detection of trace amounts of Friedel-Crafts reaction side-products with toluene as a solvent.
Read more about this topic: Benzyl
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