I like Jeff Green and I don't think he's overpaid. But if Ainge is going for flexibility, the following might work:
Jeff Green to Washington for Otto Porter and an expiring contract
For the Wizards, they'd have three wings (Green, Ariza, Webster) to go with Wall, Beal, Nene and Gortat. In the East, this might be enough to secure them home court advantage - in the first round...
From the Celts' perspective: Porter was the 3rd pick in the draft; hasn't played much at all. He had some kind of hip issue and he's been buried behind Trevor Ariza and Martell Webster. But he's got potential - on both ends of the floor. He's also half the price of Jeff Green. And because this is most likely an immediate downgrade, it puts us that much closer to Parker/Wiggins - if you're of that bent. If you're not, there's Gordon Hayward. Or maybe Porter can play.