I think there is something changed in the union between Laravel 4 and Laravel 4.1. I have 2 models.
union
$pho
You can try with DB::query() like below:
DB::query()
DB::query('(Select id,name,created_at from photos) union (Select id,name,created_at from videos) order by created_at ASC');
I guess as of know it will work. Still looking for actual solution!