Laravel - Querybuilder with join and concat

Question

Im trying to pull all users from the users table who match a certain group in the users_groups pivot table. Im using Sentry 2 from Cartalyst btw.

This works to get all users with first and last name concatenated.

User::select(DB::raw('CONCAT(last_name, ", ", first_name) AS full_name'), 'id')
        ->where('activated', '=', '1')
        ->orderBy('last_name')
        ->lists('full_name', 'id');

when i try to change it to also filter users who do not belong to a certain group I get a syntax error.

User::select(DB::raw('SELECT CONCAT(user.last_name, ", ", user.first_name) AS user.full_name'), 'user.id', 'users_groups.group_id', 'users_groups.user_id')
                        ->join('users_groups', 'user.id', '=', 'users_groups.user_id')
                        ->where('user.activated', '=', '1')
                        ->where('users_groups.group_id', '=', $group)
                        ->orderBy('user.last_name')
                        ->lists('user.full_name', 'user.id');

Any nudge in the right direction would be greatly appreciated.

EDIT: syntax error

SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in
your SQL syntax; check the manual that corresponds to your MySQL server 
version for the right syntax to use near 'SELECT CONCAT(user.last_name, ", ", 
user.first_name) AS user.full_name, `user`.`' at line 1 (SQL: select SELECT 
CONCAT(user.last_name, ", ", user.first_name) AS user.full_name, `user`.`id`, 
`users_groups`.`group_id`, `users_groups`.`user_id` from `users` inner join 
`users_groups` on `user`.`id` = `users_groups`.`user_id` where 
`users`.`deleted_at` is null and `user`.`activated` = 1 and 
`users_groups`.`group_id` = 9 order by `user`.`last_name` asc)

Answer 1

Logan's answer got my started in the right direction. I also had to remove all of the 'user.' prefixes since it was calling the Users model already I suppose. This query worked:

User::select(DB::raw('CONCAT(last_name, ", ", first_name) AS full_name'), 'id')
                        ->join('users_groups', 'id', '=', 'users_groups.user_id')
                        ->where('activated', '=', '1')
                        ->where('users_groups.group_id', '=', $group)
                        ->orderBy('last_name')
                        ->lists('full_name', 'id');

Thanks everyone! Hopefully if someone else runs into this they will find guidance with this question.