Xbox One Games with Gold titles can now be purchased via your Xbox 360
From the Major Nelson blog:
Starting today, Xbox Live Gold Members who don’t have an Xbox One yet can start building their library of Xbox One games directly from Xbox 360 by taking advantage of the Games With Gold program. You have always been able to do it this via the web and my monthly Games With Gold posts. But now, on your Xbox 360 console head to the special Games With Gold section from the link on the home page of the console and you can ‘purchase’ it there.
See the video above that will show you exactly how to do it. And don’t forget to grab your copy of Rayman Legends for Xbox One (along with Tomb Raider for Xbox 360.)