There's really no way to draw an arc in a clockwise direction, even after someone requested it four years ago?
I just tried to draw a 135 degree duct chimney (from the side) in the simplest way possible: a rectangular base with a radiused piece above, pointing to the right. While I'm a 2CAD novice, there doesn't seem to be any straightforward way to do this. None of the various ways to draw an arc will allow it in in one step, because the "end point" is unknown until the arc is drawn. I ended up drawing a 225 degree counter-clockwise arc and then drawing another one starting at the first arc's end point. Then I erase the first arc.