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Topic: Excercise doubt!!  (Read 596 times)

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Offline xshadow

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Excercise doubt!!
« on: June 03, 2021, 02:03:08 PM »
I have some doubts about what s happen in this multistep synthesis :

(I only know the reagents of each step.)

After ibx there is "heat" : I don't know if it's right my supposition
I thought that two thing could happen:

A) intramolecular dies alder...but I should get a nine-term ring so I exclude it

B) I imagine that the diene acts as nucleophile and gives an 1,4 addition with the ring closure.

But this addition generates a carbocation and I don't have any nucleophole that can react with it....and in the next step I have an acid hydrolysis.... (that I think could open the lactone/ 1,4 additopn)


Some help??
Thanks :)





Offline rolnor

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Re: Excercise doubt!!
« Reply #1 on: June 03, 2021, 04:17:55 PM »
A diene as nucleophile?

Offline xshadow

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Re: Excercise doubt!!
« Reply #2 on: June 03, 2021, 04:22:14 PM »
A diene as nucleophile?

is strange...

The only other thing is that a diels alder actually happens but I can't see it

Could I have the formaton of two ring?. or one ring  plus a 3 terms"bridge".
(Don't think that nothing happens in this step)
« Last Edit: June 03, 2021, 04:37:39 PM by xshadow »

Offline OrganicH2O

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Re: Excercise doubt!!
« Reply #3 on: June 03, 2021, 05:57:32 PM »
If you google intramolecular diels-alder you can find various examples. Long-story short, usually they make fused bicycles.
I have a Master's in organic chemistry and I am exposed to a LOT of different introductory organic chem classes in the course of my work, ranging from very basic to Harvard. I am here to refine my knowledge and consult with other organic chemistry nerds.

Offline xshadow

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Re: Excercise doubt!!
« Reply #4 on: June 04, 2021, 03:02:14 AM »
Can be something like that?


Ps: I forgot a double bond on C5-C4

Offline OrganicH2O

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Re: Excercise doubt!!
« Reply #5 on: June 04, 2021, 10:42:01 PM »
That looks right. You could also predict relative stereochemistry at carbons 1 and 2, the two stereocenters that originate from the diene, because Diels-Alder maintains the relative stereochemistry of each individual part. Stereochem at carbon 3 is trickier. This carbon would determine whether its an endo product or an exo product, which is often beyond the scope of an introductory class. You could certainly draw two diastereomers and point out which one is endo and which one is exo. But if you are currently in the class, the professor would likely accept an answer where carbon 3 has no stereochemistry indicated.

Edit: In this case, it would actually be difficult to call either of them endo, because the dienophile has two different electron withdrawing groups. So it's especially tricky, maybe just making whichever ring fusion is more stable.
« Last Edit: June 05, 2021, 01:14:54 AM by OrganicH2O »
I have a Master's in organic chemistry and I am exposed to a LOT of different introductory organic chem classes in the course of my work, ranging from very basic to Harvard. I am here to refine my knowledge and consult with other organic chemistry nerds.

Offline rolnor

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Re: Excercise doubt!!
« Reply #6 on: June 05, 2021, 05:09:30 AM »
There is a double bond missing after DA

Offline xshadow

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Re: Excercise doubt!!
« Reply #7 on: June 05, 2021, 07:36:11 AM »
There is a double bond missing after DA
yes!

The one  between C5-C4

Offline xshadow

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Re: Excercise doubt!!
« Reply #8 on: June 05, 2021, 07:38:27 AM »
That looks right. You could also predict relative stereochemistry at carbons 1 and 2, the two stereocenters that originate from the diene, because Diels-Alder maintains the relative stereochemistry of each individual part. Stereochem at carbon 3 is trickier. This carbon would determine whether its an endo product or an exo product, which is often beyond the scope of an introductory class. You could certainly draw two diastereomers and point out which one is endo and which one is exo. But if you are currently in the class, the professor would likely accept an answer where carbon 3 has no stereochemistry indicated.

Edit: In this case, it would actually be difficult to call either of them endo, because the dienophile has two different electron withdrawing groups. So it's especially tricky, maybe just making whichever ring fusion is more stable.

thanks :)
Diastereoselecctvity is a bit tricky in dies alder....the easy part is that If I have cis alkene --> syn product
BUt we haven't done very well the  relationship between the alkene and dienophile substituents

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