How do I traverse CakePHP relations?

I´m trying to traverse the relations on CakePHP models. This is the database:

I can access product attributes (product-> attributes) on a product model but I cannot access the product attributes on Ad model (ad->product->attributes).

Here is my code:

//Product Model
class Product extends AppModel {
    public $useTable = 'products';
    public $displayField = 'name';
    public $hasAndBelongsToMany = array(
        'Attributes' =>
            array(
                'className' => 'Attribute',
                'joinTable' => 'product_has_attributes',
                'foreignKey' => 'products_id',
                'associationForeignKey' => 'attributes_id',
                'unique' => true,
                'conditions' => '',
                'fields' => '',
                'order' => '',
                'limit' => '',
                'offset' => '',
                'finderQuery' => '',
                'with' => 'product_has_attributes'
            )
    );
    public $hasMany = array(
        'Ads' => array(
            'className' => 'Ad',
            'foreignKey' => 'Products_id',
            'conditions' => '',
            'order' => '',
            'limit' => '',
            'dependent' => true
        )
    );
//Ad Model
class Ad extends AppModel {
    public $displayField = 'Name';
    public $belongsTo = array(
        'Product' => array(
            'className' => 'Products',
            'foreignKey' => 'products_id',
            'conditions' => '',
            'fields' => '',
            'order' => ''
        )
    );
//Attribute Model
class Attribute extends AppModel {
    public $displayField = 'name';
    public $hasAndBelongsToMany = array(
        'Products' =>
            array(
                'className' => 'Product',
                'joinTable' => 'product_has_attributes',
                'foreignKey' => 'attributes_id',
                'associationForeignKey' => 'products_id',
                'unique' => true,
                'conditions' => '',
                'fields' => '',
                'order' => '',
                'limit' => '',
                'offset' => '',
                'finderQuery' => '',
                'with' => 'product_has_attributes'
            )
    );

// Products controller -> Action View
class ProductsController extends AppController {
    public function view($id = null) {
        if (!$this->Product->exists($id)) {
            throw new NotFoundException(__('Invalid product'));
        }
        $options = array('conditions' => array('Product.' . $this->Product->primaryKey => $id));
        $this->set('product', $this->Product->find('first', $options));
    }
}

// Ads controller -> Action View
class AdsController extends AppController {
    public function view($id = null) {
        if (!$this->Ad->exists($id)) {
            throw new NotFoundException(__('Invalid ad'));
        }
        $options = array('conditions' => array('Ad.' . $this->Ad->primaryKey => $id));
        $this->set('ad', $this->Ad->find('first', $options));

}

And here is what I do in the views:

//Products Views: snipet of view.ctp
print_r ($product);
// this prints rhe product and all associated attributes

//Ads Views: snipet of view.ctp
print_r ($ad['Product']);
//this will print only the product fields, but not the attributes associated to the product

What is wrong? How do I access the relation Ad->product->attribute from my Ad model ?