Explaining R. B. Woodward to a non-chemist, via jazz. And they were probably right, too. But that brings up an interesting question, one that applies to organic synthesis as well as every other human activity. At what point does a field become incapable of supporting Titans?
Consider organic chemistry. There were many major discoveries that had to be made before we (as a civilization) even understood what was going on. Atomic theory itself, valences, tetrahedral carbons, spectroscopy: without these and similar foundational work, you're not going to get very far. But at some point you've got enough material for the next genius to come along and make the most out of it, and I'd put Woodward in that category. He had just enough tools to make his work barely possible, and he had to invent quite a few more along the way. This gave him plenty of room to demonstrate just how good he was at organic synthesis. Complex molecules that would have been beyond structural determination in years past were now there (in theory) for the taking, but these were still well out of reach for all but the most inspired.
To switch fields of achievement, I recall reading someone's opinion once that Bach wasn't all that good, all things considered. I didn't care for that when I saw it (I like Bach very much), but the argument was that he got there "firstest with the mostest", as they said in the Gold Rush, and did such a thorough job on the musical styles of his day (counterpoint, the fugue form, etc.) that no one could ever stand on his level again. You couldn't, because Bach had already Been There and Composed That. Now, that undermines the author's original point, I think, because only a musical genius could have covered so much ground so well, but his second point stands: once Bach had done it, it was done. Anyone who composes a theme-and-variations in contrapuntal style will be compared to him, and probably unfavorably.
Similar arguments can be made across the arts and sciences. But the sciences have the advantage of not being subject so much to the whims of fashion. Picasso, I've long thought, helped create the art world in which he would be considered a great painter. (It reminds me of the way that successful organisms set up a positive feedback loop with their environment, helping to induce the conditions in which they can thrive). There are catastrophic events in both ecologies, of course, that change the requirements of fitness - Burne-Jones (to pick one example) went so far out of fashion by the 1950s and 60s that people were throwing his paintings away with the trash. But the art world has set itself up with fashion as part of its motor. Styles of painting come and go, because styles of painting have to come and go. But Newton's discoveries stand right where they were when he made them - si monumentum requiris, circumspice. Newtonian mechanics do not go out of fashion.
The only thing that can be done to alter great scientific discoveries of the past is to show how they fit into previously-unrealized larger contexts (as Einstein did with Newton). That, naturally, tends to get harder and harder as time goes on. Once the brush is cleared in science, it tends to stay cleared. That process can uncover new problems, but those are the tougher ones. This line of thought brings on talk of the End Of Science, as John Horgan put it, with which you may contrast Vannevar Bush's "Endless Frontier" (which helped establish the modern funding system for academic science in the US. My own take is that the frontier is endless for practical purposes for the foreseeable future, but not similarly endless in every direction at once.
There will, I'd say, never be another R.B. Woodward. Heraclitus aside, we have stepped into that river already, and crossed it. That's not to say that there are not great challenges in synthetic organic chemistry - there are - but it means that there is much less scope for a sky-filling fireworks display like Woodward's career. Anyone trying to recapitulate it is wasting time and effort that could be better applied.
Update: Wavefunction has thoughts on the issue here.