If by "folder" you're talking about a folder on a file server, then you will need to make use of groups. You can't use OUs or containers as security principles in the Microsoft world.
You would need to look at the concept of a shadow group to achieve what you're after if you wanted to persist with your current strategy.
Shadow groups are more of a concept than a particular item. They're just normal group into which you maintan a list of users found within an OU (with or without including members of subtrees). Typically, the group membership is synchronised periodically
via a script set up as a schedule task.
I'm not sure how familiar you are with Powershell, but it's the easiest way to achieve this sort of basic administrative task - assuming you're running Server 2008 R2 or later (or Windows 7 or later, but you wouldn't typically schedule something like
this on a workstation).
Using Powershell, you can do this with three lines:
Import-Module ActiveDirectory
$users = Get-ADUser -SearchScope onelevel -SearchBase "OU=Users,OU=Company,DC=YourDomain,DC=com" -Filter *
Add-ADGroupMember -Identity "YourGroup" -Members $users
Obviously, you'd have to make sure the content in red is changed to suit your environment.
Cheers,
Lain
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