|Yet another chance to critique my structures...|
Conceptual simplicity: While ruthenium-catalyzed metathesis (cross-metathesis or ring closing) is fairly mechanistically complex, the reaction (concept and retrosynthesis) is simple enough to teach to a sophomore. I suspect that its simplicity may be overly tempting to chemists; I've found myself led astray when planning syntheses in attempts to incorporate a RCM into routes.
Operational simplicity: It's pretty hard to think of an easier reaction -- degas, dump, dump, stir and heat. Filter through a silica gel pad, bam, there's your pure product.
Web 2.0: Olefin metathesis may be the only reaction that not only has a company, but it has a blog. All Things Metathesis is a great resources for, uh, all things metathesis.
Silly personal reasons: Like just about every other natural product synthetic route during the time that I graduated, there was a RCM in my thesis research. But there's a much more personal reason I feel a certain bond with Grubbs chemistry -- I found out that Professor Grubbs won the Nobel Prize while I was preparing to get married. (Earlier that month, I remember idly speculating about whether or not olefin metathesis had been around long enough to garner attention for a Nobel.) For some reason, it made my wedding and honeymoon just that much sweeter knowing that
If I could think of a single word to sum up Grubbs' metathesis chemistry, it would be "cool." And that's why I chose it for my favorite reaction.
Runners up: Haufe halofluorination, Fu's sp2-sp3 catalysts, the Finkelstein.