The answer of your question is little tricky, nothing has been there in cakephp documentation
What I have done in the similar situation was given below:
Step 1: I have define one routing rule in routes.php as
Router::connect('/posts/*',
array('controller' => 'posts',
'action' => 'handleRedirection')
);
Step 2: I have created one function handleRedirection in posts controller
function handleRedirection(){
$url = str_replace('posts','news',$this->request->url)
$this->redirect($url,'301');
}
See in the above example I am using 301 permanent redirection, so you can do something like this.