Which territory controlled by Hitler stretches is the farthest east

The territory that Nazi Germany managed to control at its peak, stretched all the way from the Atlantic coast in Western Europe, to the plains north of the Caucasus Mountains in what is now Russia.

The easternmost part which Germany managed to control, though very shortly, were the plains north of the Caucasus Mountain Range. That happened during the attempt of the Germans to invade Russia. Despite their initial gain of these strategic territory, the Germans didn't managed to keep hold of it for long, as the Russians put all their troops and power in there and eventually won over the German armies. That was the first big blow for Hitler, also marking the start of the end for the domination and militaristic expansion of Nazi Germany.