Really lots of delusional arsenal fans in this thread. Hopefully the United, Swansea and Anderlecht games reminded you of why current Arsenal is not a contender for EPL/CL, and won't be one IMO as long as Wenger's in charge there.
Dortmund won more titles and got a lot further in the CL than Arsenal recently.
Sanchez/Ozil were FORCED OUT of their clubs, which is why they HAD to move. None of the huge clubs were in for them, so they went for Arsenal as the best option available (Sanchez could choose with Juventus and Liverpool, not exactly huge clubs nowadays).
The situation with Reus is different. He won't be forced out, his contact isn't expiring and the clause isn't going away. I believe that if Real/Barca/Chelsea/Bayern won't come for him in the summer, he'll stay another year at Dortmund and move next summer. A move to Arsenal is a move sideways at best and will ensure he'll be without a major trophy for a while.
BTW I will be very surprised if Sanchez will stay in Arsenal more than 2-3 seasons, if he continues being that good. He's too good for them, just like Suarez and Bale were.