During long meetings, my thoughts turn to all sorts of useful topics - pressing things like, "If we ever meet intelligent aliens, what will they know about chemistry compared to us?" (I'm having to make some assumptions with that thought, of course, because any aliens that can send us so much as a ham sandwich from another star system already have us totally outclassed). But the question doesn't have to involve any space travel; you could just as easily ask what we'd be doing now if the history of the science had gone differently. Did it have to evolve the way it did?
For example, there are an awful lot of old carbonyl-condensation reactions - aldol, Claisen, Dieckmann, etc. Are these inevitable early discoveries? You could make a case for "yes", because the starting materials are often such basic organic chemicals (aldehydes, esters), and their reactions would probably be among the first things explored. Besides, the reactions of stabilized carbanions are a cornerstone of organic chemistry, and even if things got a bit out of order you'd think that this would have to still be the case, The same goes, and more so, for nucleophilic substitution. I don't see any sort of organic chemistry getting very far without the discovery of things like the Williamson ether synthesis and the Finkelstein reaction, and the principles behind them.
The wild cards would probably be organometallic reactions. Grignard reagents might be an example of things were discovered earlier than they should have been. We still don't know all the details of their formation and reactivity, a hundred years on. And on the other side, did it have to take so long for the palladium couplings we all use to be discovered? After all, palladium was already known to do a lot of interesting organic chemistry, even fifty years ago. But as late as the 1980s, palladium-catalyzed carbon-carbon couplings were a bit exotic. Think, though, of what the field would look like if someone had stumbled over the Suzuki coupling in, say, 1949. . .
The history of oxidation and reduction, though, could easily be moved around, since there are so many means to accomplish similar ends. It's possible to imagine a world where the early organic synthesis papers aren't so full of Jones reagent and the other chromiums, but where some sort of permanganate or ruthenium reagent was the favorite. As for reduction, like him or hate him, where would boron reagents have been without H. C. Brown? ("Probably more widely used", I can hear some people muttering. . .)
That brings up the whole topic of personality. Historians frown on the "great man" viewpoint, but inside one scientific discipline it's hard to ignore it. Organic synthesis would certainly exist if R. B. Woodward had never been born, but it's for certain that it wouldn't look the way it does now. . .