Methoxymethyl ether protecting alcohols with

Silyl ether protected alcohols (eq 5) have been converted directly into the corresponding bromides with PhaP and CBr4. The reaction works best if 1.5 equiv of acetone are added. Tetrahy-dropyranyl ether protected alcohols have also been directly transformed into the bromides using this reagent combination. The reaction has been reported to proceed with inversion of configuration (eq 6). If unsaturation is appropriately placed within a tetrahydropyranyl (eq 7) or a methoxymethyl (eq 8) protected alcohol, cyclization occurs to afford tetrahydropyrans. The conversion of an alcohol to the bromide without complications with a methoxymethyl protected alcohol in the molecule is possible (eq 9).i ... 

The benzyl ether is prepared in a similar manner to the methoxymethyl ether, that is, by reaction of the conjugate base of the alcohol with benzyl bromide in an SN2 reaction. An example of a sequence that employs a benzyl ether protecting group is illustrated in the following sequence ... 

Protection of tertiary alcohols. Methylthidiiiethyl (MTM) ethers have the advantage that they can be prepared from tertiary alcolols (7,135), but the disadvantage that they are prone to oxidation. They can be convcrtcil into 2-mcthoxycthoxymethyl (MEM) ethers, methoxymethyl (MOM) ethers, or ethoxy methyl (EOM) ethers by reaction with... 

In order to achieve controlled polymerization from die bdk ligand, an ethanol moiety is introduced to the phenol site to provide a primary alcohol site, and a less sterically crowded enviromnent for initiation (Figure 4). The alcohol requires protection in order to prevent deprotonation under die basic reaction conditions required for the ester and ketone condensation. A number of protecting groups were screened for this purpose, and one promising strategy involves methoxymethyl (MOM) protection. The formation of the MOM ether proceeds in nearly quantitative yield. After the condensation, the MOM group can be removed with aqueous HCl in THF. 

The methoxymethyl (MOM) and jS-methoxyethoxymethyl (MEM) groups are used for protecting alcohols and phenols as formaldehyde acetals. These groups are introduced by reaction of an alkali metal salt of the alcohol with methoxymethyl chloride (chloromethyl methyl ether) or -methoxyethoxymethyl chloride. An... 

Different alcohols and protected alcohols (as hemiacetals, silyl, methoxymethyl or phenyl ethers) were lithiated at the d-position to give the corresponding organolithium compounds. In the case of alcohols, a previous deprotonation of the hydroxyl functionality is required. The chiral intermediate 197 was prepared from the phenylsulfanyl derivative 196 first by deprotonation followed by carbon-sulfur bond cleavage with LiDTBB at low temperature. The reaction of the dianionic system 197 with y- and d-lactones in the presence of cerium(III) salts gave, after hydrolysis, spiroketal pheromones 198 (Scheme 2.27) [163]. 

A mild procedure for the appendage of MOM groups to acid-sensitive substrates is illustrated by the protection of the allylic alcohol in Avermectin derivative 259.1 using [(methoxymethyl)thio]-2-pyridine (259 2) sitver(I) Inflate and sodium acetate in THF at room temperature [Scheme 4.259],479 Primary secondary and tertiary alcohols and phenols are methoxymethylated in good yield though phenols are slower to react. Reagent 259.2 (bp 66 °C/0.088 kPa) is easily prepared in 75% yield by the reaction of pyridine-2-thiol with dimethoxy-methane activated by trifluoroborane etherate. 

Challenged by this synthetic problem, our laboratory sought to develop an ether transfer protocol that stereose-lectively generates ether functionality and provides additional synthetic handles enabling the development of strategically novel approaches to the synthesis of structural units common to polyketide natural products." As an extension of Bartlett et al. s carbonate process initiated with IBr, the methoxymethyl-protected homallylic alcohol... 

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