Piv esters are usually hard to deblock beacuse of steric hindrance. Have you tried LAH in THF?

Look at this link:

http://ion.chem.usu.edu/~tchang/Chem7300/Carbohydrate/Chapter%203%20Protecting%20Groups.pdf

There are some examples of Piv group deprotection

Perhaps you can find another examples in " Protective groups in Organic Synthesis" Theodora W.Green, Peter G.M. Wuts, Wiley, 1999.

Sincerely,

AD

Rapid and efficient deprotection of pivaloyl esters can be achieved by absorption onto alumina and microwave irradiation as reported earlier by

--- Ley, Steven V.; Mynett, Donna M. Synlett (1993), (10), 793-4.

Good luck