Well from reading this article it seems that the only to play these games is if you already own them digitally or own the disk, doesn't appear to be a market place for them on the Xbox One.

I have bought literally 100s of xbox 360 digital games over the years,i have the exact same gamertag but i don't see a single option to play any of the games i payed for in the past.

To be honest i think they have made it really difficult for this backward thing to work and access easily .

Have you checked you game library, ready to install part?

Yep Nothing there only Xbox One Stuff