[Random Coils]

I'm looking for good references or procedures by which to hydrolyze a pinacol protected phenylboronic acid.  I need to obtain the free boronic acid (PhB(OH2)), but I'm having trouble removing the pinacol.  I'm working with a polymer, and it is not water-soluble in its pinacol ester form.  Any ideas?

[sjb]

I'm looking for good references or procedures by which to hydrolyze a pinacol protected phenylboronic acid.  I need to obtain the free boronic acid (PhB(OH2)), but I'm having trouble removing the pinacol.  I'm working with a polymer, and it is not water-soluble in its pinacol ester form.  Any ideas?

Some of the things I've looked at in the past (sorry, old project, don't have the refs to hand) included NaIO4 (sometimes buffered), treating with BCl3, heating with acetone. I'll see if I can find a reference or two in my folder...

S

[lavoisier]

I'm looking for good references or procedures by which to hydrolyze a pinacol protected phenylboronic acid.  I need to obtain the free boronic acid (PhB(OH2)), but I'm having trouble removing the pinacol.  I'm working with a polymer, and it is not water-soluble in its pinacol ester form.  Any ideas?

First, I would advise you to prepare a 'similar' non-polymer bound pinacol boronic ester and try the most obvious hydrolysis methods (such as the ones you can find in Greene's Protective Groups) on that. Then you can transfer the method to your more valuable material.

Second, from the literature one gets the impression that these esters are extremely hard to hydrolyse. Actually, I prepared some pinacol boronates from aryl halides and bis(pinacolato)diboron in dioxane with KOAc as the base, and in some cases the boronic ester spontaneously decomposed to the boronic acid, even in these extremely mild conditions.

I wouldn't start with boron halides and oxidizing agent. I'd try the simplest ones first, like THF/H2O/HCl or THF/H2O/KOH(or LiOH), at room temperature or at reflux if it doesn't work. Of course I'm assuming that your polymer will be soluble in some water-miscible organic solvent. If it isn't, everything becomes more complicated as you may guess...