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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: AlphaScent on April 19, 2015, 05:22:13 PM

Title: Diels Alder
Post by: AlphaScent on April 19, 2015, 05:22:13 PM

Do you think I can get this reaction to go to completion?  Maybe heat and Lewis acid??  Is the diene reactive enough?

(I know cyclopentadiene is very reactive and will be more so with a activating methyl group)

The homoketone (unconjugated) bothers me a bit but it is the only way to get the synthesis I want.  I can show the rest if someone would like.

Title: Re: Diels Alder
Post by: discodermolide on April 19, 2015, 08:42:37 PM

You probably don't need the catalyst. That will tie up the 2 carbonyls.
But you need to think about the stereochemistry of the product. That chiral auxiliary will have some effect.

Title: Re: Diels Alder
Post by: AlphaScent on April 19, 2015, 08:52:09 PM

Hmm... I was going off of notes from class and worked out the TS and believe I have the right stereochemistry.

I have been known to be wrong though haha.

Attached is what is in the notes given by the professor.

Cheers!

Title: Re: Diels Alder
Post by: AlphaScent on April 19, 2015, 08:55:52 PM

Wait....The diene will approach from the opposite face of the auxillary....The notes and I are wrong!!!

The auxillary should be the other way, correct??

The fact the double bond is trans also makes me think.  Is that the Endo product...seems to me it is.

Title: Re: Diels Alder
Post by: discodermolide on April 19, 2015, 09:22:13 PM

which C=C are you talking about, the one in the first scheme or the second one?

Title: Re: Diels Alder
Post by: AlphaScent on April 19, 2015, 09:52:09 PM

The C=C from the second scheme is straight from my notes given by the professor. 

The first is my method for a reaction in a synthesis. 

I have to think if the C=C with the methyl (methylcyclobutadiene) will be on the correct side (regiochemistry).

I am referring to the first scheme.  I may have my regiochemistry wrong.

Title: Re: Diels Alder
Post by: discodermolide on April 19, 2015, 10:04:37 PM

OK, well is the top face of the C=C not blocked by the auxiliary?

Title: Re: Diels Alder
Post by: orgopete on April 20, 2015, 10:28:26 AM

I have little faith in my ability to predict a reaction's enantioselectivity, so I cannot make those predictions. I'd simply use the example from your notes as a guide. However, you've made a significant change in the dienophile by moving the double bond. I'd doubt you'd get that product.

Title: Re: Diels Alder
Post by: AlphaScent on April 20, 2015, 12:40:47 PM

Orgopete,

I agree. The dieneophile is no longer electron poor.  Some thought must be taken. 

I will post my answer to the question.  It may be completely wrong.