Methoxymethyl (MOM) ether group is generally used to protect the hydroxyl group. However it is also used to protect the amino group.
The general scheme of using of this protecting group in organic synthesis is summarized below:
FORMATION OF MOM ETHER GROUP & PROTECTION OF HYDROXYL GROUP
The following reagents and reaction conditions may be used to introduce an MOM group on -OH.
i) Chloromethyl methyl ether, CH3OCH2Cl (abbr. as MOMCl) in presence of N,N-diisopropylethylamine, i-Pr2NEt (DIPEA) at R.T.
ii) Chloromethyl methyl ether (CH3OCH2Cl) in presence of NaH in THF.
iii) Methylal (dimethoxymethane), CH2(OMe)2 + P2O5 in CHCl3 at 25 oC. The yields can be improved if the solvent, CHCl3 is dried over P2O5 overnight prior to the reaction.
iv) CH2(OMe)2 in presence of Trifluoromethanesulfuric acid (TfOH) in CH2Cl2. However tertiary alcohols are not protected in good yields.
STABILITY OF MOM ETHER GROUP
* Stable between pH=4 to pH=12.
* Inert towards variety of oxidizing and reducing agents; bases; nucleophiles; and electrophiles.
* However it is sensitive to acids or reagents containing them. E.g. Undergo dissociation with Zn/HCl.
* Also sensitive to halogens.
REMOVAL OF MOM ETHER GROUP
Since the MOM group is an acetal, it can be cleaved by acid hydrolysis. In general, it can be removed by boiling in methyl alcohol in presence of trace of conc. HCl. Other methods using variety of acids in organic solvents can also be employed to remove the protection.
ILLUSTRATIONS
1) The alcohol group of 3-bromopropan-1-ol is protected using MOM ether group to carry out the conversion of -Br to -CH2OH via Grignard reaction to get 1,4-butanediol as final product. The last step involves both removal of MOM group and decomposition of addition product in the Grignard reaction.
