MEM protection of carbohydrates

[gravenewworld]

Would this work? I can't seem to find any examples in Scifinder of carbohydrates where all the -OH groups are protected with either MEM or MOM. Is there a reason why? Will this not work? I know using MEM and MOM are pretty standard for protecting alcohols, why in the case of carbohydrates does there seem to be little or no examples? There are examples in the literature of where people have added methyl groups n-butyl groups to make the ethers on all of the -OHs, would a MEM or MOM group work as well?

 

[MrSid]

Remember that the sugar is a hemiacetal and the MEM and MOM ethers are acetals so there will be reactivity issues if the cleavage reactions are needed later. Most of the reactions on sugar OH's are based on reactions that can be run in water since the sugars are largely insoluble in other polar aprotic solvents- it limits the electrophilic functions that can be used to react with the OH to ones that are able to be catalyzed and run in H2O. The common one is to make the acetates, and then use these (because they are differently soluble from the starting sugars) in ways that allow removal of a few groups and replace the protecting groups in aprotic solvents.

The sugar's hemiacetal is always targeted first for changing the solubility to make it a relatively stable acetal. It will usually allow for switching to MeCN or DMSO as a solvent, and a targeting of the OH's according to steric availability, and primary OH reactivity.