Many of my readers are professional chemists, but many aren't. For those who've only had sophomore organic (or less), it sometimes comes as a surprise to find out that we actually use a lot of those reactions that you have to learn.
That's a strange thing about chemistry as compared to most of the other hard sciences. I don't think that much that you learn in a second-year physics class comes up in the day-to-day life of a physicist, and the same goes (and how) for most biologists. But I'm here to tell you: we professional organic chemists really do Fischer esterification, the Knoevenagel condensation, and a lot of those other ancient reactions. Not just once in a while, either - we do 'em every day of the week. My lab, for example, has been wrestling the last few days with forming and using a particular Grignard reagent, and Grignards have been a standard part of undergraduate labs for generations.
Why do we stick with these moldy reactions? Because they work, for one thing. Reducing an aldehyde with sodium borohydride, for example, is a procedure that's been around for a good forty years. But it's a mighty rare aldehyde that won't reduce cleanly with the stuff. It's fast, it's cheap, and it's generally easy to clean up the reaction, so why not?
Another reason is that these reactions are close to the fundamental principles of organic chemistry. If you're going to make an ether from an alcohol, for example, it's hard to see how that's going to happen without an oxygen attacking a carbon center somewhere along the line. I mean, you're forming an oxygen-carbon bond, so you can't avoid it. And oxygen is so electronegative, you have to figure that it's going to have some sort of negative charge built up on it, so it's going to be attacking something with a partial positive charge. . .and there's the good ol' Williamson ether synthesis, the classic nucleophilic substitution. To have a completely different ether synthesis, you'd almost have to have a completely different form of oxygen.
And that brings me to an observation that I've made before - that you can be a fine medicinal chemist using nothing but reactions from a sophomore organic textbook. It's a bit humbling to realize that, because catching on to that fact tells you where chemistry stands in drug discovery: not as an end in itself, but as a means to an end. And if those means turn out to be reactions that an eighty-year-old grandmother could learn to run, and that are older than she is on top of it, well, fine. We're not here to use the latest hot reaction, unless it can speed up making a drug. Because that's the point.