Methyl ethers, as protecting groups

The hrst synthesis of pelargonidin chloride used methyl ethers as protecting groups for the phenolic hydroxyls during the Grignard addition step."" ... 

Silyl Ethers.—Examples of the usefulness of t-butyldimethylsilyl ethers as protecting groups are nicely illustrated in Schemes 17 and 19. Methyl a-D-gluco-pyranoside reacted with a molar equivalent of t-butyldimethylsilyl chloride in pyridine to give the 6-0-(t-butyldimethylsilyl) derivative in virtually quantitative yield, and sucrose reacted with 3.5 molar equivalents of the silylating reagent to give almost exclusively r,6,6 -tri-0-(t-butyldimethylsilyl)sucrose and traces of mono- and di-substituted products. In the presence of an excess of sucrose, a mixture of 6 -, 6,6 -di-, and r,6,6 -tri-0-(t-butyldimethylsilyl)sucroses was obtained. 

Enol ethers of saturated 3-ketones are not usually obtained directly from the ketone and therefore are of little importance as protective groups. However, enol ether (52) has been used instead of the bulkier 3-dimethyl ketal to protect the 3-ketone during angular methylation to (53). ... 

We said earlier that simple methyl ethers are inappropriate as protecting groups for OH because they are too hard to take off again. That is usually true, but not if the OH is phenolic—ArOH is an... 

The stability of ethers and mixed acetals as protecting groups for alcohols varies from the very stable methyl ether to the highly acid-labile trityl ether. However, all ethers are stable to basic reaction conditions. Hence, ether or mixed acetal protecting groups specifically tolerate... 

MetHoxym0thyl ethers of phenols. These ethers are readily prepared by reaction of chloromethyl methyl ether with a suspension of the dry sodium salt of a phenol in benzene or toluene. They are useful as protective groups because they are stable to alkali, to potassium cyanide, to Grignard reagents, and to n-butyllithium, but can be hydrolyzed when desired by very gentle treatment with acid. They are cleaved more easily than the corresponding benzyl ethers. Examples of synthetic uses are as follows. 

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