Concept: Concept: Sodium Alkynide Alkylation4m
Part of the synthetic cheat sheet taught you guys how to make carbon-carbon bonds and that's what I want to focus on in this topic. I really just want to destroy the entire concept of organometals and sodium alkynide alkylation.
Basically, you guys know, this is the only way to make carbon-carbon bonds in orgo one is through organometals. Strong sodium alkynides are really commonly used organometals and because they happen to be strong nucleophiles. What that means is that since they're strong nucleophiles, they're often paired or reacted with alkyl halides because those are strong electrophiles.
What we can do is we can get a negative on a carbon to be attracted to a positive on a carbon and bam. You have a new carbon-carbon bond, which is very important because synthesis relies on making bigger molecules from smaller ones. So if you can add carbons, that's really important.
But for these, for sodium alkynides, we're not going to just need to know that it's a nucleophile and attacks an electrophile. We're going to need to know a few more things. How to generate the alkynide. That means alkynide synthesis, making it from scratch. We need to know how to do that. Also, after you've done your reaction, you also need to know how to transform the triple bond afterwards, so there's a lot to know here. We need to know how to make the alkynide. Then how to use it and then how to lose it, how to do different things to it.
Once again, I had this graphic that showed different nucleophiles. The ones that we're going to be dealing with are mostly on this page because I want you guys to get special practice with these are the alkynides and the alkyl halides.
So what we're going to do first is we're going to start from kind of ascending hardness. We're going to start with the easiest problem. It's not easy, but it's not that bad and we're going to work our way to progressively harder and harder problems, where I'm going to take you further and further back in the synthetic process and you're going to have to figure out everything from the very beginning.
But in this case, like I'm telling you right now, this is not such a bad question. Let me coach you through it and see if you can get it. Because notice that right now – first of all, I'm already starting with a triple bond. That's awesome because if you're going to notice, I have three carbons in this molecule. I have four carbons in the other.
What does that mean that must have happened at some point? If I added carbon, if you added carbon that means you must have used an organometal. Like I said, the most common organometal in this chapter is going to be sodium alkynide. I already have a triple bond, so that's a huge giveaway that I just need to use that triple bond.
Basically, what you should be thinking is how many carbons do I need to add to the triple bond to make four and then what do I need to do to that triple bond afterwards so it looks like a double bond. It looks like that. That was enough hint. I'm just trying to coach you guys so this isn't totally like a train wreck. I'm going to stop the video and you guys try to answer it the best that you can.
Problem: Propose a synthesis:3m
Problem: Propose a synthesis:5m
Problem: Practice 3: Propose a Synthesis5m
For the following sequences of reactions, work through all the different reactions and then write the final product(s). Assume only the predominant product is formed at each step. You must indicate stereochemistry with wedges and dashes. You must draw all stereoisomers produced as predominant products and write "racemic" under the structures when appropriate. Assume no rearrangments take place. You do not need to draw any of the molecules synthesized along the way, just the final product(s).
Show how you would carry out each of the following reactions. You do NOT need to draw the mechanisms
Provide the reagents required for the following transformations. Note, that some of these methods will require more than one chemical step. All the steps and reagents must be included.
Give structures for the products of each of the following reactions:
Provide only the major product for the following synthesis. Stereochemistry is not important.