Well, this post needs updating. In it I mentioned never running a Prins reaction again since the 1980s, nor any photochemistry, and today what do I find myself doing? Both of them, although not at the same time.
I am, fortunately, not running the Prins this way. But even bringing it up at all recalls to me a key part of my education. When I first joined my graduate school research group, I was put to making some tetrahydropyran systems. I was handed a synthesis, drawn up before my arrival, of how to make the first one, and like most first-year grad students, I gamely dug and and started to work on it.
I should have devoted a bit more thought to it. I won't go into the details, but it was a steppy route that relied, in the final ring-closure step, on getting the cyclic ether to form where one of the partners was a neopentyl center. The organic chemists in the audience will immediately be able to guess just how well that went.
So I beat on it and whacked at it, getting nowhere as I used up my starting material, until I was finally driven to the library. In the spring of 1984, that was a different exercise than it is now, involving the 5-year Chemical Abstracts indices and an awful lot of page flipping. (I haven't so much as touched a bound volume of CA in I don't know how many years now). If you were a nomenclature whiz, you could try looking up your compound, or something like it, in the name index, but a higher-percentage move was often to look up the empirical formula. That gave you a better shot, because (if it was there at all) you could see how CA named your system and work from there.
To my great surprise, the second set of collective indices I checked (the good ol' 9th), yielded a direct hit on an empirical formula, and the name looked like exactly what I had been trying to make. The reference was in Tetrahedron, which we most certainly had on the shelf, and I zipped over to see if there was any detail on how to make the stuff.
There was indeed. A one-stepper Prins cyclization gave just the ring system I'd been trying to make, and that was one step from the intermediate I needed. I just stared at the page, though. I honestly couldn't believe that this was real (as I mentioned, I was in about my second month of grad school lab work). Surely the synthesis I'd been given was the way to make this stuff? Surely the people responsible for it had checked the literature before drawing it up? (After all, it had only taken my a few minutes to find the stuff myself). Surely I couldn't just make the ring in one afternoon using two starting materials I could buy cheaply from Aldrich?
Well, surely I could. And that's just what I did, and got my project moving along until the next interesting difficulty came up a couple of months later. But I still recall standing there in the Duke chemistry library, looking at that journal article "with a wild surmise" that perhaps I should check things out for myself next time instead of just taking everyone else's word. It took a couple more lessons for me to really grasp that principle (Nullius in verba!, but it's helped me out a great deal over the years. I have the 27-year-old photocopy I made that afternoon in front of me now. It's a good reminder.