After drawing it out im 90 percent certain that number 4 does not belong i base it on the follwoing judegement: first i was way off in my first estimate the end product cannot have the Ru group therefore that eliminates 3 so that leaves 1,2,4, 2 is correct like you stated it is the intermediate before getting number 3 its the step right before the Ru and the other cH group leave so that leaves number 1 and 4. 4 is incorrect because when the cyclobutane forms with the Ru the next natural step would be for it split away from the molecule however, since this has to be the first step after adding the catalyst that would be out of place so 1 would have to be right also because it is the first step in the progrection of the catalyst. I could be wrong but i just dont see it any other way, is it ok Dan