Readers may remember the incident a couple of years ago where a paper was published claiming the synthesis of some very odd-looking 12-membered ring compounds. Prof. Manfred Christl of the University of Würzburg noticed something odd about this reaction, though, namely that it had already been run over a hundred years ago and was known to give a completely different product. (As I pointed out here, though, you didn’t need to unearth the ancient literature to know this; ten minutes of looking through the modern stuff would have done the trick, too).
Well, Christl’s back with another takedown of some improperly assigned weirdo 12-membered rings. This time, it’s Cheryl Stevenson of Illinois State that gets the treatment, with this paper from last year that claims several interesting ring structures from 1,5-hexadiyne and base. Christl had trouble believing the mechanism, and on closer inspection had trouble believing the NMR assignments. Then, on even closer inspection, he assigned the structure as a simple isomerization of one of the triple bonds, and found that this exact reaction (and product) had first been reported in 1961 (and several times afterwards). Not good.
As it turns out, I almost certainly made some of the compound myself, by mistake, back in mid-1983. That was the summer before I started my first year of grad school, and I was doing work in Ned Porter’s lab at Duke. One of the starting materials I needed was. . .1,5, hexadiyne, which you couldn’t buy. So I made it, in real grad-school fashion. I homocoupled allyl Grignard to get the 1,5-hexadiene (which even if you could buy back then, we didn’t). Then I reacted that with bromine and made the only six-carbon molecule with four bromines on it that I ever hope to make. Reacting that with freshly prepared sodium amide in ammonia gave the smelly di-yne, in crappy yield after distillation. I can still see it: me heating up a column full of glass beads, then turning to Steve, the postdoc in the next hood, and making a bad joke about Herman Hesse while David Bowie’s “Modern Love” played on the radio. . .ah, those days, they will not come again.
At any rate, I went on to react the compound with bases under different conditions, trying (in vain) to alkylate both of those terminal alkynes, and thus passed the last of my summer, in exactly the way my two previous summers of research had passed: unsuccessfully. This latest paper, though, makes me think that I was probably turning my starting material instead into exactly the diene that Christl is talking about. I should have hit the library harder myself, although (to be fair) there are references that tell you that you can do that alkylation, and digging through the literature was a good deal more time-consuming back then that it is now.
That lab accident, you say? Well, that happened when I was making a big batch of sodium amide. You start that prep off like a Birch reduction – condense a bunch of liquid ammonia into a flask, and start chucking sodium metal into it. The big difference is that you add a bit of ferric chloride to the mix, which kicks things over at the end. After you’ve dissolved your sodium, to give you the bronzy purple-blue of solvated electrons, you take the flask out of the cold bath to let the ammonia reflux. At that point, the whole thing suddenly clears, dramatically revealing grey lumps of sodium amide rolling around on the bottom of a pond of plain ol’ ammonia, without a solvated electron in sight. (I have, in years since, seen a couple of people refer to the blue stage of the reaction as sodium amide, which it ain’t, and I can get quite cranky and pedantic about it).
One afternoon I was whipping up a batch of this stuff, when something starting going on inside the flask. I don’t recall what made me take a look at the ammonia solution, but since there was so much bronze gorp on the side of the one-liter three-neck, I had to lean in and look down near the central joint. Whereupon my hair wound itself immediately around the greased shaft of the overhead stirrer, pulling my head in toward the whole setup and jamming my nose into the side of the flask. I fumbled for the switch of the stir motor, feeling like George Jetson as I shouted for someone to give me a hand, and watched with interest as the dry ice bath bubbled along an inch away from my face.
Steve the postdoc came to my aid, shutting off the grinding motor which was doggedly trying to wind me headfirst around the stirrer shaft. We unreeled my hair from the whole contraption, with me cursing foully and Steve merrily making jokes of the “Hair today, gone tomorrow” kind, with side comments about me getting too wrapped up in my work. Those days, as I said, will not come again.