How to use TODO tags in org-mode without defining headings?

When I'm writing down a few notes in org-mode :

note 1
note 2
note 3

And then want to make 'note 2' a TODO item, I need to turn it into a headline, as such :

note 1
* TODO note 2
note 3

But now, 'note 3' belongs to the 'note 2' headline. The only solution I know is to turn the other notes into headlines as well.

* note 1
* TODO note 2
* note 3

But that's tedious.

I've tried

# TODO note 2

But that doesn't work either.

How to get todo-keyworded items without actually changing the outline ?