Regardless of whether we'd like Deng or not, why would Chicago deal him to us?
It only makes sense for Chicago to trade him in one of the following scenarios:
1) To a team with cap space / non-guaranteed contracts. This would allow the Bulls to clear his contract, and have enough space to sign two max free agents; or
2) To a team that has a departing free agent, in a sign-and-trade.
The Celtics don't fit under either of the above scenarios, unless the Bulls for some odd reason want to give Ray Allen a big deal. I think the Bulls may instead look to another team that has space / a departing free agent that otherwise might not be able to attract talent as good as Deng. Teams in that category include Minnesota, New Jersey, and Toronto (in a Bosh sign-and-trade).