Portals do not "render only the object visible through the portal."
They simply cull the room if the camera is outside the room or if it's looking away from the portal.
So In your example it should look like this:
A camera has to be in a room for portals/rooms to work.
You can also do something like this if you want to create a cave/outside inside system:
Rather than having two rooms next to each other, this has one room surround another and have portals look into the two rooms, like looking into a cave from outside.