Greenland was known to Europe since long before 1492. In fact, Leif Erikson reached modern Canadian lands around the year 1000, coming from Greenland. That journey was forgotten, but he chose a logical exploration path by starting from the westernmost land known.
So why didn't Columbus do the same? Seems a much bigger leap to try the mid-Atlantic first. Surely they knew, via dead reckoning and the like, the Greenland coasts were much more west than Portugal? In the summer and fall, the ocean around south Greenland should be ice-free enough to navigate.
In fact, in the year 1500, Portugal sent someone to Greenland to find a Northwest Passage to Asia. Why didn't they do this first with Columbus?