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Questions tagged [pericyclic]

For questions concerning all aspects of pericyclic reactions, their use in synthesis, and the orbital analyses used to describe them.

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What is the driving force for Claisen rearrangements?

I came across this mechanism (3,3 sigmatropic rearrangement). Why does the allyl vinyl ether have the ability to rearrange itself giving a new product? What drives the reaction? Is it the instability ...
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Cis Orientation of dienophiles orientation of groups maintained in Diels Alder

When I was reading about Diels-Alder reactions, I was confused about the cis and trans rules for dienophiles, as shown below. The text told me that "a cis dienophile will generate a ring with cis ...
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Endo/Exo for same length bridges

I'm looking at a cycloaddition that produces a bicyclic intermediate, there are two different ways of doing the addition which can be described as endo/exo. However, all three bridges are the same ...
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Claisen rearrangement in substituted ring

This is an example of Claisen rearrangement, property of allyl vinyl/phenyl ethers. I believe that the allylic migration should take place to the position ortho to both $\ce{-CH3}$ and $-\ce{OR}$ ...
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Reverse electron demand Diels-Alder

Why is the reverse electron demand Diels-Alder reaction much rarer than the normal one? By reverse electron demand, I mean one with an electron-rich dienophile and an electron deficient diene. In ...
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Is it possible to form an 8 carbon ring using a Diels-Alder reaction?

I need to convert the starting material to the product on the right but I was wondering if it was possible to use a Diels-Alder reaction and use $\ce{KMnO4}$ to cleave the ring.
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Pericyclic Reaction

Does anyone know what PhMe is used for in this reaction (how it contributes to the mechanism?)? I thought pericyclic reactions only needed heat? Thanks!
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Pericyclic Reaction Question [duplicate]

So I read that s-cis conformations with a carbonyl bond react more readily in Diels-Alder pericyclic reactions than those without carbonyl bonds. However, why does this effect of increased reactivity ...
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Diels-Alder reaction question

In class, we learned that Diels-Alder reactions only occurs with s-cis conformations and that conformations like those in cyclopentadiene are permanently locked in a cis-transformation and that is why ...
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Explaining stereochemistry in a sigmatropic 1,3-alkyl migration

I have quite a bit of difficulty in explaining sigmatropic rearrangement reactions. Consider the following reaction: How do I explain the formation of the shown product? When simply moving the ...
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Differentiating between Prins reaction / ene reaction experimentally

The Prins reaction – stepwise addition of an alkene to a carbonyl compound – leads to the same product as a concerted ene reaction. This is illustrated here with tin tetrachloride as a Lewis acid, ...
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Stereoelectronic effects in torquoselectivity of 4π electrocyclic opening

Thermal 4π electrocyclic ring openings of cyclobutenes to form butadienes are known to proceed in a conrotatory manner, consistent with the Woodward–Hoffmann rules. However, there are two different ...
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Why is a racemic mixture formed in the Diels-Alder cycloaddition?

Why is a racemic mixture formed in the Diels-Alder cycloaddition? I note that for both endo and exo products, either enantiomer can be formed. Why is this so?
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Can the Smirnov-Zamkow reaction be described as a pericyclic process?

The Smirnov-Zamkow reaction involves the reaction of 2-butyne and chlorine in the presence of a Lewis acid catalyst to afford a dichlorocyclobutene: At first glance, it appears to be an example of a ...
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Reaction of substituted furan with methyl vinyl ketone with subsequent rearomatisation

I am supposed to provide a mechanism for the above transformation. I observed that the order of substituents on the product is same as that on furan, and since furan undergoes Diels–Alder reactions, I ...
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Treatment of 2-vinylbicyclo[2.2.2]oct-5-en-2-ol with potassium hydride

What happens when this bicyclic compound is treated with KH in THF? Does $\ce{KH}$ simply act as a base here? $\ce{H-}$ from $\ce{KH}$ could potentially act as a nucleophile, but I don't find any ...
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Theoretical basis behind orbital correlation diagram for pericyclic reactions

When discussing pericyclic reactions, the Woodward-Hoffman rules allow one to predict whether a reaction will be thermally/photochemically allowed. This has been discussed in many questions on chem.SE,...
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Application of the Woodward-Hoffman rules to a [14+2] cycloaddition (follow up)

This is a follow up question to another question I made earlier. I put some of this information into my own notes just so I can get my head around this. So just to clarify. Does the Woodward Hoffman ...
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Application of the Woodward-Hoffman rules to a [14+2] cycloaddition

I am just doing some pericyclic practice problems and I am just trying to understand the Woodward Hoffman rules. The attached picture is a problem I attempted that was checked against the answers but ...
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In an electrocyclic reaction with two pi bonds that result in a trans product, is a mix of products seen?

When I look at the highest occupied molecular orbital, the two methyl groups will end up being trans to each other. I realized based on which conrotation direction both methyl groups take that two ...
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What is the driving force behind sigmatropic reactions?

I am studying sigmatropic reactions in context of pericyclic reactions and I am confused about the overall purpose of this type of reactions. I know that sometimes in sigmatropic reactions, more ...
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Reaction between 1,2-dicyanoethylene and 2-phenylbuta-1,3-diene in toluene and heat

I believe this may be a Diels-Alder reaction, but the benzyl group on the edge does not serve a an electron donating group and more as a stabilizing group. I am at a loss for what reaction would take ...
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Can vinyl alcohol react as a dienophile in Diels-Alder reactions?

For my organic chemistry exam I needed to synthesize cylcohexanone and in one of the steps a Diels-Alder reaction was required. I chose to use vinyl alcohol followed by an elimination reaction to get ...
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Why is the endo product the major product in a Diels-Alder reaction?

I understand that the endo product is, at least in all cases in my textbook, the major product in a Diels-Alder reaction. However, I don't understand why this is the case. The explanation in my ...
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Direction of arrows in electrocyclic reactions [closed]

We recently started learning about pericyclic reactions and this is a step from a mechanism I'm working on for an assignment. I believe that the arrows on the right are better than the arrows on the ...
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Symmetry forbidden cycloaddition in the Wittig reaction?

My textbook (Klein) describes the mechanism for the Wittig reaction as a [2+2] cycloaddition, followed by a collapse of the ring. As far as I'm aware, [2+2] cycloadditions are symmetry forbidden, ...
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Pericyclic Reaction Mechanism

We've been asked to draw the mechanism for the following pericyclic reaction: I know that the tin tetrachloride will act as a Lewis acid and activate the one of the carbonyl groups of the ethyl ...
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Why can't we use orbital correlation diagrams for sigmatropic rearrangements?

In Ian Fleming's Molecular Orbitals and Organic Chemical Reactions book, he describe the use of correlation diagram as a method for predicting whether pericyclic reactions will be allowed/forbidden on ...
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hydrolysis of chlorocyclopropane rings

Why is the hydrolysis of trans-1-chloro-2,3-dimethylcyclopropane more rapid than for the cis-isomer? (Liverpool Poly., Finals 1985) (9-marks) Trans: the projection given had the two methyl ...
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Orbital and state correlation diagram for ring-closure of pentadienyl to a cyclic allyl

This is an exam question. I am to construct the orbital and state correlation diagram for one of the reaction below (disrotation or conratation). Also, I should explain whether the reaction is ...
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Kinetic isotope experiment used to distinguish radical and concerted mechanisms for the Diels Alder reaction

In the Pericyclic Reactions Oxford Primer it is written that: the deuterium substitution of the hydrogen atoms in the diene and dienophile that participate in a possibly Diels-Alder reaction, ...
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Relative rates of two acyclic dienes in the Diels-Alder reaction

As for factors that affect the rate of the Diels Alder reaction, having an s-cis conformation is primary. But in a case as shown below, what makes the second diene react faster compared to the third? ...
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why are cyclic dienes much more reactive?

Cyclic dienes are very reactive, for example cyclopentadiene in room temperature, it even dimerizes. What is the factor that indicates such reactivity of cyclic dienes ?
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Why can anthracene, but not phenanthrene, take part in Diels–Alder reactions?

Both anthracene and phenanthrene seem to be structurally similar, with three aromatic rings. The middle rings in particular seem to be similarly activated towards cycloadditions.
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What is the difference between Fukui FMO approach and Woodward-Hoffmann rules?

If I understand correctly Frontier MO-theory is based on the perturbation theory of reactivity and the Woodward-Hoffmann rules consider conservation of orbital symmetry. Does FMO use symmetry ...
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Deciphering stereochemical notation in electrocylization reaction

I not agree with this solution, for me the red bond formed must be a dotted line in the drawing, and the hydrogen atom musn't be represent with a dot. Am I right or not?
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Orbital correlation diagram for the cleavage of cyclopropylmethylene carbene

In the last exam we were asked to rationalize the mechanism of the cyclopropylmethylene carbene cleavage into acetylene and ethylene. In the lecture we discussed pericyclic reactions (cycloadditions, ...
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How to classify the hydride shift in the following diazacyclopenta[cd]pentalene system?

How is this hydride shift reaction type called? I think it's not one of following types: cycloaddition (Diels Alder) electrocyclic ring opening sigmatropic rearrangement ene reaction cheleotropic ...
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Stereoselectivity of 1,3-dipolar cycloadditions

How do the 1,3-dipolar cycloadditions follow the endo rule as in the reaction below, where the anti diastereoisomer is formed predominantly?
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Singlet/triplet oxygen cycloadditions

Why can singlet oxygen participate in cycloaddition reactions while triplet oxygen, on the other hand, can't?
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Grubbs, Wittig & hydroboration reactions and Woodward-Hoffmann rules

Several organic mechanisms I know involve [2+2] cycloadditions and retro-[2+2] cycloadditions, namely: The Wittig reaction Hydroboration of an alkene Olefin metathesis (using Grubbs' catalyst) How ...
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Why is it the middle ring of anthracene which reacts in a Diels–Alder?

I'm wondering why maleic anhydride adds to the middle cycle of anthracene, and not the outer two. I would have expected that a Diels–Alder with the outer ring would be better, because I expected a ...
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Torquoselectivity: Disrotatory ring opening

In organic chemistry lecture we discussed the beginning of the Woodward Hoffmann Rules with a key step of the vitamin B12 synthesis. (The initial paper from their work can be found here: http://pubs....
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Is ozone an electrophile in the ozonolysis reaction?

From the above mechanism it is clear to see that the electrons from the double bond attack one of the terminal oxygens in ozone, thus meaning it's an electrophile. How can this be? If you draw the ...
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What is the mechanism of a 1,2-hydride shift?

What is the mechanism of a 1,2-hydride shift? I read that there is an aromatic intermediate, in that the intermediate obeys Hückel's rule. However, Wikipedia doesn't offer any further explanation. ...
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Exceptions to motif: nucleophile attacks electrophile

I hear this motif - nucleophile attacks electrophile - all the time with regard to organic chemistry. Are there any exceptions? I think this statement is always true in general because it's a ...
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Why is the exo product formed in the Diels–Alder reaction between furan and maleic anhydride?

For most Diels–Alder reactions, the major product is endo because there are favourable interactions between the newly forming pi bond and the electron withdrawing groups of the dienophile. Why is the ...
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Do eta-4 benzene ligands participate in Diels Alder or other cycloadditions?

While refreshing myself on denticity to answer another question, I started to read about hapticity, which is the coordination of a ligand through multiple continuous atoms. A famous case is ferrocene (...