Boss extrude exclude area

I always used Acad and now for a while Solid works.

See my sketch, does anyone have a hint for me how I can exclude the area inside the elbow? The checkbox “merge result” is not selected. And I can’t select only the area outside the elbow. Must I make a plane and intersection, so I can select or create a elipse as contour or area?

SolidworksDrawings And Detailing