Sort post by last commented

For this you can use WP_Comment_Query.

The query will be

    $comments_query_args = array(
        'post_type' => 'post',
        'number' => 5,
        'status' => 'approve'
    );
    $comments_query = new WP_Comment_Query();
    $recent_comments = $comments_query->query($comments_query_args);