(use srfi-1)

(define mylist '((key1 . peanut) (key2 . butter) (key3 . jelly) (key4 . time) (key5 . (1 2 3 4))))

(define (non-nested-keys alist #!optional fields keep?)
  (let ((keys (remove null? (map
			     (lambda (curr-key)
			       (if (not (list? (alist-ref curr-key alist)))
				   curr-key '())) (map car alist)))))
    (if (null? fields)
	keys
	(if keep?
	    (lset-intersection eq? fields keys)
	    (lset-difference eq? keys fields)))))

;; Get keys
(non-nested-keys mylist)

;; Get only keys matching desired
(non-nested-keys mylist '(key2 key234565 key4) #t)

;; Remove the following keys and return everything else
(non-nested-keys mylist '(key2 key234565 key4) #f)