Booleans work on solid 3D objects, not on 2D objects.
If you want to perform booleans on 2D objects you're best off using Illustrator, Intaglio, Inkscape, or some similar program -- or a high end modeler that supports operations on 2D geometry (some high end 3D modelers let you do things like slice a 3D form with a 2D scalpel, and so on, too).