OK, solid chemistry around here today. It looks as if I'll be running a ring-closing metathesis reaction soon. Nobel Prize in 2005, all over the chemistry journals for years. . .and I've never had occasion to use one until now. And when I think about it, there are quite a few other reactions in that category for me.
For example, I'm not at all sure that I've ever done a directed ortho-metalation. I've come close a few times, and I couldn't absolutely swear that I've never done the reaction, but none come to mind. No Fischer indole synthesis for me, because I've always been able to buy the indoles I need, and the same thing applies (fortunately) to the widely disliked Skraup cyclization for quinolines. I've never done an Eschweiler-Clarke reaction, although there have been several times I've needed to form methyl amines, and it probably would have been a good idea.
I've never done any of those multicomponent condensation reactions (Ugi, Passerini, etc.), partly because I've never done much combinatorial chemistry. And I've never done a Rosenmund reduction, but jeez, in this day and age, who has? No Julia olefination, no Fries rearranagements, no Kolbe-Schmitts (or Kolbe anything, come to think of it). And no Paterno-Buchi reactions, because I haven't really done any photochemistry for about twenty years.
I suppose the biggest gaps in my record are the RCM (soon to be filled) and the directed metalation (unless I can think of one that I've blocked from my memory somehow). Most of the other big ones I've done at one point or another, albeit perhaps only once or twice: the last time I ran a Wurtz coupling, on purpose, anyway, was twice in the summer of 1983. I have run a lot of the obscurities as well, of course (Shapiro elimination, anyone?) And I have a lot of fondness for some lesser-known reactions, such as the Prins cyclization, which got me out of a tight spot in my first year of grad school (I've been grateful ever since).
So here's my chem-geek question for the laboratory-bound part of my readership: what famous reactions have you never done? Have you been avoiding it for some reason, or have you just never needed the thing (and wondered why it's so darn famous)? Confess below!