Which of these two pathways is better for Robinson cycloaddition?....

  • Thread starter Thread starter Aristotelis1999
  • Start date Start date
AI Thread Summary
The discussion centers around a question from an organic chemistry exam regarding the synthesis of 4-phenyl-2-cyclohexenone. The main focus is on the retrosynthetic analysis, which identifies one aldol condensation reaction and two potential Michael addition reactions. The preferred pathway involves using 2-phenyl-2-propenal and acetone, as the alternative option reduces the nucleophilicity of the a-carbon due to charge delocalization in the benzene ring. A key point raised is the necessity of a base to generate the active enolate, with emphasis on the stability and ease of generation of the enolates. The discussion concludes with insights from the teacher, highlighting that aldehydes undergo aldol condensation more rapidly than ketones, and the potential side reactions with 2-phenylacetaldehyde complicate the synthesis.
Aristotelis1999
Messages
2
Reaction score
1
TL;DR Summary
Target molecule: 4-phenyl-2-cyclohexenone. 2-phenylacetaldehyde + 3-buten-2-one or 2-phenyl-2-propenal + acetone?
So this was a question on my orgII exam yesterday. The target molecule is 4-phenyl-2-cyclohexenone. By retrosynthetic analysis there is only one possible aldol condensation reaction, but two possible michael addition reactions afterwards. My "guess" was that the best one is 2-phenyl-2-propenal + acetone because in the other case the negative charge is delocalized throughout the benzene ring reducing the nucleophilic character of the a-carbon and also activating the ring in which case EAS could take place with the ring acting as the "Michael Donor". Please correct if I was supposed to post this question in another forum. Thank you a lot in advance.
 
Chemistry news on Phys.org
You need a base to generate the active enolate. Which enolate is easier to generate? Which one is more stable?
 
TeethWhitener said:
You need a base to generate the active enolate. Which enolate is easier to generate? Which one is more stable?
Well, there's an obvious answer for that. But anyway, I went and asked my teacher and it turns out the same exact exercise was solved in the textbook. The answer was what I said, but for very different reasons. Aldehydes undergo aldol condensation in base much faster than simple ketones. So, the issue with using the 2 - phenylacetaldehyde is aldol condensation with another same molecule as a side reaction.
 
  • Informative
Likes TeethWhitener
Very interesting. Good to know.
 

Thread 'Solubility of MgSO47H2O in water'

It seems like a simple enough question: what is the solubility of epsom salt in water at 20°C? A graph or table showing how it varies with temperature would be a bonus. But upon searching the internet I have been unable to determine this with confidence. Wikipedia gives the value of 113g/100ml. But other sources disagree and I can't find a definitive source for the information. I even asked chatgpt but it couldn't be sure either. I thought, naively, that this would be easy to look up without...
View full post »

Thread 'Why does having 8 valence electrons make an element inert?'

I was introduced to the Octet Rule recently and make me wonder, why does 8 valence electrons or a full p orbital always make an element inert? What is so special with a full p orbital? Like take Calcium for an example, its outer orbital is filled but its only the s orbital thats filled so its still reactive not so much as the Alkaline metals but still pretty reactive. Can someone explain it to me? Thanks!!
View full post »

Similar threads

Naming question; Michael Aldol Condensation
Replies
3
Views
5K
Which will give better neuclophilic addition reaction?
Replies
1
Views
2K

Hot Threads

Recent Insights

Back
Top