Filter 'login_redirect'
.
Sample code, not tested:
add_filter( 'login_redirect''wp_login', 'wpse_78150_login_redirect' );
function wpse_78150_login_redirect( $url )
{
# uncomment the next line for debugging
# var_dump( wp_get_current_user() ); exit;
if ( ! current_user_can( 'custom_role' ) )
return $url;
return admin_url();
}