Everyone, in this example question, it says that the human body can be highly stereo selective in the types of drugs used to treat illnesses. Now this is true. Remember, when it comes to something like aspirin, one enantiomer of aspirin works on treating our headaches, while the other one doesn't. Now, if a researcher develops a cancer fighting drug, as displayed below, determine which of the following compounds will be best in creating it after reacting with our palladium catalyst, diethyl malonate, and sodium ethoxide.

Alright. So, this is our product. Now, this question looks more complicated than it really is. Remember, in this reaction, we have the retention of our r and s configuration. So if we look, here is our bond that's dashed.

They're telling us it's an s configuration. Before this enolate was attached, we had our palladium catalyst. And before that, we had a good leaving group. That good leaving group was x.

It must have also had an s configuration. When we reacted with our palladium catalyst, that flipped the bond making it r, and then it reacted with our diethyl malonate and sodium methoxide. So, it reacted with the enolate form, and that's how we got back to s. So all we have to do here is: This was our initial reactant. It had an s configuration.

That means that a is out and d is out. So the answer is going to be either c or b. Now what's the difference? Let's see. In b, it says S-3-chloro-3-methoxypentene-1-ene.

And in this one, it is s-5-methoxypent-1-ene-3-ol. Alright. So, if we look at this product, this is positions 1, 2, 3. It's position 3 that's being affected. In position 3 here, we have an OH group.

In position 3 here, we have a Chlorine. Remember, OH is not a good leaving group. We could change it into a good leaving group if we protonated it into water, but here at the moment, OH is not a good leaving group. Chlorine is a great leaving group. Chlorine can be kicked out by our palladium catalyst, and then that can be replaced later on with our enolate.

So the answer here is option B. Again, the question looked more complicated than it really is. Our final product is s, which means our initial reactant also had to be s. That immediately tells you that it's either b or c. C doesn't work because OH is not a good leaving group.

So we wouldn't even be able to get rid of this x with our palladium catalyst. So that means that b is our final answer. Right? So that would be our final answer for this particular example question.