I've been stuck with this for some time. I just don't see it. As the reactant is Pd(0), I think oxidative addition will happen to the bromine. Then I would say an insertion reaction happens. However this would form a 7-membered ring which isn't as stable as a 5-or 6-membered ring and isn't even in the final product.
Then I tried complexating it with the double bond next to the ether. However I don't see what use the Pd could have from there. Maybe deprotonate the alpha-carbon which would give a hapto-3 complexation? But what next, I wouldn't know. Any help would be appreciated!