It would be suicidal for Israel, and totally insane to do it. Logic, pragmatic caution and common sense are needed. Assad certainly isn't going to preemptively attack Israel, in case anyone has not noticed, he's a wee bit busy right now, and it would divide his forces and not be good strategy for him, and so he won't do that.
World Jewish Congress: Nazi train treasures must go to rightful owners (Reuters)
from the article: Israel doubts Assad possesses S-300 system, but has good reason to worry