The synthesis of any novel compound is a big discovery be it made by conventional methods or something new.
I have to disagree with that.
Say I have something like, nitrotetrazole, and I alkylate it giving the 2-methyl-5-nitrotetrazole, and the 2-ethyl, 2-propyl, 2-butyl, 2 pentyl, 2-hexyl. Those are then published. then somebody does the same thing with octyl. I would have to argue that this is not a big discovery unless this compound had certain properties of interest.
Or in drug chemistry, when somebody is doing combinatorial chemistry, making hundreds of target drug molecules, only the ones with the desired drug properties are cared about, the remainder fall by the wayside and maybe get a mention in the paper. It would be hard to argue that those wayside structures are "big discoveries"