[Monoamine]

I'm wondering if anyone knows if MgBr₂ (magnesium bromide) can be used to attach a Br group to an aldehyde?

Also, if I remember this correctly, to make MgBr₂ one has to use dioxane instead of ether as the solvent, since Br₂ reacts with the ether.

This would be useful for making acetal protecting groups.

[Babcock_Hall]

MgBr₂ is a salt, not a Grignard reagent.  This salt is an ionic substance, which is a very different situation from what one has in elemental bromine, Br₂.  Maybe you can draw out the transformation that you would like to do.

[rolnor]

I think you know far to little to be able to design a way to make new protecting groups, you need to learn more.

[Monoamine]

Essentially, what I'm trying to do is halogenate the carbon in formic acid. The reason for this approach, as opposed to the classical approach of using acetic anhydride, is that where I live acid anhydride happens to be schedule 1 precursor (I think they use it in the clandestine manufacture of heroin or something) so unfortunately I can't use acetic anhydride. There are ways to create acetamide protecting groups with acedic acid as a catalyst, but the problem with this specific protecting group is that it isn't very easy to deprotect the amine again late (it can be done, but from what I read the yield is not very good and the process is rather lengthy (i.e. refluxing in HCl for about 24 hours).
That's why it would be more efficient to use something like a t-butyl carbamate protecting group, since it can be deprotected more efficiently.
But to form a t-butyl carbamate, I would essentially have to first form an amine with a formic acid group attached to it, so that I can then esterify it via a Fischer esterification...

[rolnor]

This can be usefull. Again, you need to do some more reading.
https://en.wikipedia.org/wiki/Carbamic_acid
https://en.wikipedia.org/wiki/Di-tert-butyl_dicarbonate