Probably noone ever needed to do this before
.
I guess you'll need to (temporarily) shorten the item marked "2" to its endpoint (where you want to snap to). Then - assumed you have "Snap media items to nearby media items" enabled and set to (at least) "up to 1 track away" in the snap settings - item 1 will snap there.
Maybe alternatively there is a possibility to place the cursor to the end of the source of item 2 (and then snap to the cursor)? I guess it would be doable via ReaScript, if SWS doesn't have it already.
I can't hide that I'm curious, what's the goal?