Here’s another approach. Begin with a rectangle whose corners are located at the center points for the quarter circles at the corners.

Extrude out from the sides and ends by a distance equal to the radius of the corner quarter circles.

Add a filled circle with a number of sides divisible by 4, and with a radius the size of the extrusions. Remove 3/4 of the cicumferential vertices, leaving the center vertex, and a wedge of less than 90 degrees.

Duplicate the wedge 3 times, (for a total of four instances of the wedge, and move the wedge so that the center vertex is co-incident with the corner of the original rectangle, and the circumferential vertices are between the vertices of the extrusion.

Make edges or faces between the extruded sides and ends, and the wedges.

Takes longer to describe than to do.