Weird O Chem question

[euphaire]

Dear SDN members,

I've been trying to figure out the following problem for 2 hours now. I looked at Claisen condensation reactions, 1,2/1,4 reactions, Michael additions, etc, and I still can't figure out the mechanism for the problem below......It's 1am now and I should really sleep :'( Please help!

The solution is A. But why? How? What are the names of the reaction(s) involved? I tried drawing the electron arrows and...usually I can work out the mechanisms quite well but not for this one. I'd really appreciate some help.

Thank you!!

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[Mithril]

You're reacting a malonic ester with a very strong base and an alkyl halide. Remember that the hydrogen atoms attached at the alpha carbon are relatively acidic. You'll also have CO2 as a product. See where you can go from there.

 

[hematosis]

Dear SDN members,

I've been trying to figure out the following problem for 2 hours now. I looked at Claisen condensation reactions, 1,2/1,4 reactions, Michael additions, etc, and I still can't figure out the mechanism for the problem below......It's 1am now and I should really sleep :'( Please help!

The solution is A. But why? How? What are the names of the reaction(s) involved? I tried drawing the electron arrows and...usually I can work out the mechanisms quite well but not for this one. I'd really appreciate some help.

Thank you!!

produce?

C is also a product, but the alpha hydrogens are pretty acidic and can deprotonate.

 

[euphaire]

Yes...I believe the strong base will deprotonate the alpha carbon right in the middle. This alpha carbon becomes negatively charged. I'm not sure where to go next.

Would this anion attack the CH3CH2Br in a E2/SN2 or something else happens? Still, I don't see how in the end, the product is A. It seems that either the original molecule got cleaved or somehow one of the carbonyl was completely removed...


P.S. I only took a first year O-chem course a long time ago. Due to many reasons, I'm teaching myself those new reactions and concepts. That's why I'm stuck on a problem like this without a clue. Please elaborate more because I really can't think of how the reaction would go from there. Thank you in advance.

P.S: Is there a special name for this type of reaction?

 

[hematosis]

Yes...I believe the strong base will deprotonate the alpha carbon right in the middle. This alpha carbon becomes negatively charged. I'm not sure where to go next.

Would this anion attack the CH3CH2Br in a E2/SN2 or something else happens? Still, I don't see how in the end, the product is A. It seems that either the original molecule got cleaved or somehow one of the carbonyl was completely removed...


P.S. I only took a first year O-chem course a long time ago. Due to many reasons, I'm teaching myself those new reactions and concepts. That's why I'm stuck on a problem like this without a clue. Please elaborate more because I really can't think of how the reaction would go from there. Thank you in advance.

P.S: Is there a special name for this type of reaction?

these problems are like puzzles.
Product C can react with itself, with the original starting material. The original starting material can also react with itself after the first detonation. And, also remember that they can also react with the alkylhalide (the ethylbromide). I would draw them all out and see if you can find the product. Also, as mentioned before, look to see if there is a c02 decarboxylation, that usually throws people off.

 

[Mithril]

P.S: Is there a special name for this type of reaction?

It's a nucleophilic substitution, ester hydrolysis, and decarboxylation of a malonic ester. Chances are that if you see a malonic ester, an alkyl halide, and a strong base, you're going to have a final product answer similar to A. They may show you other potential products, but choose the BEST answer, ie. the product that will be formed in the largest quantities.

Reference: http://www.chem.ucalgary.ca/courses/351/Carey/Ch21/ch21-5-2.html

 

[Rabolisk]

This is called malonic ester synthesis and is a standard reaction/set of reactions in Orgo II. Not a weird problem at all.

Deprotonation, alkylation (SN2), hydrolysis, and decarboxylation.

 

[BerkReviewTeach]

Dear SDN members,

I've been trying...

Does the OAT have five choices per question?

 

[loveoforganic]

Yes, for parts, I think

https://www.ada.org/oat/oat_sample_test.pdf

 

[TwoPaddles]

1. base deprotonation
2. attack to the CH2 next to the Br
3. heat it to remove one of the OEt groups.

that simple 😉