You need this as a cutting path, right?
You need to duplicate the layer. And then lock the original layer just to be sure.
Then select all and apply the Pathfinder "Unite" from the pathfinder panel (might be called differently, it's the top left one)
The result will leave you with a couple of very small elements. You might need to delete those - unless you also want to offset the cutting path, so it has some distance to the original objects. In that case you can use Effect > Path > Offset path. Do the offset. Then Object > Expand appearance. Then Pathfinder Unite again.