What are these pericyclic reactions?

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In summary, the conversation revolved around the potential for an intramolecular [2+2] photocycloaddition or an intramolecular Alder-ene reaction with a cyclopropyl ring. The instability of the cyclopropyl ring and its potential role in the reaction were discussed, with the suggestion that it may open and leave a temporary positive charge on the quaternary carbon. The stabilization of this positive charge by the carbonyl oxygen and the potential rearrangement of protons were also mentioned.
  • #1
CrimpJiggler
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First one:
feea75c6577d97b85310a41fb53f06bb.png

is this an intramolecular [2+2] photocycloaddition?

And this one:
aa86e2304119606f2535da3b00648cdc.png

I'm fairly confused about this one. Could it be an intramolecular Alder-ene reaction? Whats confusing me most is that cyclopropyl ring up there. I know they're pretty unstable and I read that they open during electrocyclisations and stuff like that so I'm wondering if it plays a role in this reaction.
 
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  • #2
It's been a while since I studied chemistry, but since no one answered, I'll throw my 2 cents.

For #2:

It's a fairly safe bet that the cyclopropane ring will open, leaving a temporary + on the quaternary carbon. There are two things that make this easier: the carbonyl oxygen can donate electrons through the conjugated double bonds, and the + is stabilized by the methyl group.

Then, I think, the 6-membered ring will close with rearrangement of protons.
 

1. What are pericyclic reactions?

Pericyclic reactions are a type of organic chemical reaction that involves the reorganization of electrons in a cyclic transition state. They are characterized by the simultaneous formation and breaking of multiple bonds, and typically occur through a concerted mechanism.

2. What are the key features of pericyclic reactions?

The key features of pericyclic reactions include: the involvement of a cyclic transition state, the simultaneous formation and breaking of multiple bonds, and a concerted mechanism. They also often exhibit stereoselectivity and regioselectivity, and can be thermally or photochemically induced.

3. What are some common examples of pericyclic reactions?

Some common examples of pericyclic reactions include: the Diels-Alder reaction, the ene reaction, the electrocyclization reaction, and the sigmatropic rearrangement. Other examples include the Cope rearrangement, the Claisen rearrangement, and the Nazarov cyclization.

4. What is the difference between pericyclic and radical reactions?

The main difference between pericyclic and radical reactions is the mechanism by which they occur. Pericyclic reactions occur through a concerted mechanism, involving the reorganization of electrons in a cyclic transition state. Radical reactions, on the other hand, occur through a stepwise mechanism involving the formation of reactive intermediates known as radicals.

5. What are the applications of pericyclic reactions?

Pericyclic reactions have a wide range of applications in organic synthesis, including the synthesis of complex natural products, pharmaceuticals, and materials. They are also used in the production of polymers, dyes, and other industrial products. Additionally, pericyclic reactions play a key role in biological processes, such as photosynthesis and DNA repair.

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