A few years back here on this site when I would write about synthetic photochemical methods, the reaction in the comments section was, well, mixed. There would be interest, but there was always a strain of “Bunch of academic publications that will never amount to anything in the real world” as well. The amount of blue light that I see coming from fume hoods these days, though, seems to indicate that photoredox chemistry has indeed found a home, because it can do things that are very hard to accomplish by other means.
Another method in that category is electrochemistry, and although I have done a fair amount of photochemistry (sensitized and not) over the years, I (like most synthetic organic chemists) had never really done much with the electrodes. The field had a reputation (pretty well-deserved, too) of being very finicky and hard to reproduce. You would see some interesting reaction done with an electrochemical rig and think “Yeah, that would be pretty useful if it weren’t electrochemistry”. That’s what led the Baran group a couple of years back to try to standardize and popularize such techniques. The jury is still out on that one – it’s not like the journals have filled up with electrochemical synthesis, but at the same time you do see more of it than you used to, and colleagues of mine have had some success with it in the med-chem labs. That’s certainly due to the commercially available equipment, which (as was the plan) has lowered the barrier to trying such things out. Indeed, photoredox chemistry and electrochemistry have some synthetic overlap, since they’re fundamentally based on oxidation and reduction potentials.
Inevitably, we’re now seeing more crossovers between these two. Here’s a new paper on electrophotochemical substitution of aryl fluorides. These are reactions that you would draw out as classic nucleophilic aromatic substitutions, heating them up in DMSO or something with base. And there are a number of reactions here that would probably work out fine that way, since the reaction goes best with electron-deficient fluoroaryls, but there are several that would be hard to realize the classic way, too. Similarly, here’s a recent paper on trifluoromethylation and a look at two other such transformations.
It’s not for nothing that drawing organic chemistry mechanisms is referred to as “pushing electrons”, because that’s what we do as we break and form bonds. These newer methods are getting down to that as directly as possible – there is no more “atom-efficient” reaction possible than shoveling electrons directly into a molecule (or better yet, a specific bond). Those electrons can be coming right out of an electrode, or the “electron shovel” can be some catalytically generated species that turns around to deliver another load. But either way, it does make you wonder if organic synthesis is setting out on a different path than the classical reactions have taken. I don’t know if the combination of photochemistry and electrochemistry is going to take off on its own. Neither do its practitioners, of course. It’s a new enough field, though, for there to be some really useful reactions hiding in it that no one has yet come across.
That’s not to say that all the older reactions are going to go away, and especially not any time soon. They’re already being augmented, though, and I would be willing to bet that in the coming decades there will be more and more of these direct electron-pushing processes used. You’d expect to see them especially in process chemistry and specialty chemicals, where some particular molecule’s preparation needs to be optimized and it’s worth spending the time and effort to come up with bespoke conditions. That’s still the reputation that photochemical (and especially electrochemical) methods have, that they need too much tweaking and dinking of conditions to get them to work well, but that’s what the synthesis of high-volume high-value materials is all about. . .