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Topic: Tetramethrin  (Read 7451 times)

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Offline Rutherford

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Tetramethrin
« on: February 18, 2013, 04:17:40 AM »
Tetramethrin is a key substance of many household insecticides. This compound belonging to pyrethroids of the 1st generation can be obtained by esterification of chrysanthemic acid with alcohol X. Synthesis of the latter is given below.

Write down the structural formulae of O-R, and X. Note that the transformation of O into P is an isomerization with retention of the carbocyclic skeleton leading to the most stable isomer.

What is the first reaction about (anhydride+alkene)?
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Offline discodermolide

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Re: Tetramethrin
« Reply #1 on: February 18, 2013, 04:19:33 AM »
It is a Diels-Alder reaction.
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Offline Rutherford

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Re: Tetramethrin
« Reply #2 on: February 18, 2013, 04:45:30 AM »
Read now about it. Found very scary example, but this one seems fairly easy. I think that O is the compound attached. What happens in O :rarrow: P? It is isomerization, but what is the stablest isomer?
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Offline discodermolide

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Re: Tetramethrin
« Reply #3 on: February 18, 2013, 04:50:24 AM »
That's the correct structure. The next step is a series of C=C migrations catalysed by Pd so what is liable to be the most stable isomer?
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Offline Rutherford

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Re: Tetramethrin
« Reply #4 on: February 18, 2013, 04:54:58 AM »
Don't know. This seems like stable to me. The double bond requires an angle of 120°, and in the ring with 6 C atoms, the angle is perfect. What would be more stable?
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Offline discodermolide

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Re: Tetramethrin
« Reply #5 on: February 18, 2013, 05:00:13 AM »
How about the double bond in this structure?
O=C1OC(C2=C1CCCC2)=O

bloddy Smiles won't draw it how I want!
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Offline Rutherford

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Re: Tetramethrin
« Reply #6 on: February 18, 2013, 05:08:31 AM »
I think it's the delocalization, right?
I think that R is the attached compound. If it is, what happens in the last step with formaldehyde?
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Offline discodermolide

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Re: Tetramethrin
« Reply #7 on: February 18, 2013, 05:10:33 AM »
Yes conjugation
That compound is not R
« Last Edit: February 18, 2013, 05:27:22 AM by discodermolide »
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Offline Rutherford

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Re: Tetramethrin
« Reply #8 on: February 18, 2013, 05:14:23 AM »
What happens then with ammonia? I thought that it is an acid ahydride amonolysis to produce amide and acid.
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Offline discodermolide

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Re: Tetramethrin
« Reply #9 on: February 18, 2013, 05:16:26 AM »
I think it re-cyclises to
O=C1NC(C2=C1CCCC2)=O

You can take
O=C(O1)CCC1=O

with ammonia to give

O=C(N1)CCC1=O
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Offline Rutherford

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Re: Tetramethrin
« Reply #10 on: February 18, 2013, 05:26:28 AM »
Wait, I think it gives the compound I wrote, but on heating (t), a water molecule leaves, and the compound you wrote is made. Is this the final product (attached). I thought that the hydrogen attached to nitrogen is acidic because of nitrogen and it leaves the molecule, then N- is made, and in an nucleophilic addition the compound I attached is made. True?

*Forgot the double bond  ::).
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Offline discodermolide

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Re: Tetramethrin
« Reply #11 on: February 18, 2013, 05:28:32 AM »
That will do.
That is the final compound.

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Offline Rutherford

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Re: Tetramethrin
« Reply #12 on: February 18, 2013, 05:31:34 AM »
Okay, thanks.
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Offline Rutherford

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Re: Tetramethrin
« Reply #13 on: February 18, 2013, 05:41:48 AM »
Which of the following acid derivatives could easily form esters in reaction with alcohols?
a) anhydride; b) methyl ester; c) amide; d) hydrazide

I would say a). Not sure for c) and d). How to determine this? What property to aim for?
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Offline discodermolide

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Re: Tetramethrin
« Reply #14 on: February 18, 2013, 06:25:27 AM »
You need to look for good leaving groups and the reaction conditions.
certainly a), other esters can be formed form methyl esters by transesterification, you can't usually form esters from amides, nor hydrazides
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