In Organic Chemistry, Diels-Alder reactions are a great way to make carbon-carbon bonds
Many of you have probably seen this reaction before. But if not…just wait! It is sooo cool!
Alright – Let’s get to it!
I pulled this question for my “student request list.” Someone asked if I could do a Diels-Alder (DA) reaction. Well, here it is..
But before we jump right in, let’s take a general look at the DA reaction.
The Diels-Alder reaction forms a 6-membered ring
In every DA reaction, at the heart of it, you will be forming a 6-membered ring. Not only that…but you can get multiple stereocenters at the same time. Yea…it is a powerful reaction!
We will not worry about the stereochemistry today. Just focus on the ring.
This is what you are looking to make with each DA reaction. And the best way to figure this out is by numbering all your carbons.
You want to start by numbering all your carbons in your organic molecule
Find the carbon chain that has all the double bonds you need and number it – #1 to whatever you need.
If you want to use IUPAC numbering…go for it! Basically, you are numbering to keep track of everything.
Now, look for your “key players” in the reaction
Start by “pulling out” the carbon structures you need to form your 6-memebered ring:
Diene – Two double bonds in conjugation (right next to each other)
Dienophile – The isolated double bond. And it will not be a carbonyl (C=O); these are only used with specific reactions.
So far…not too bad, right?
Next, line everything up and make your 6-memebered ring
Now, we need to get everything lined up so we can see how to put our “key players” together.
Why did I put carbon 1 and 10 close to each other? Why not the other way? Think about a stiff wire. It is easiest to put the ends together.
Now, Start drawing your arrows…
..and then simply draw your bonds between carbons 1 and 10 and carbons 4 and 9.
But what about the rest of our carbons?
This is why we numbered all our carbons. We know what numbers need to go together.
Form the top structure we see that carbons 4 and 5 go together and carbons 8 and 9 go together. But I am pretty sure you did not need me to tell you that.
Now, arrange them so they fit.
What would it look like if we had the whole molecule?
Great question! And here it is…
This time I am only labeling the carbons that form the main 6-membered ring (our “key players”). So…what will the final structure look like?