[Rutherford]

In the question, it is said "easily", but transesterification needs catalysts and I don't think that a high yield could be obtained. So, it would be only a).
Your help is really appreciated. Thanks very much.

[Rutherford]

The 1stgeneration pyrethroids are photochemically unstable, which stimulated development of new types of pyrethroids (of the 2nd and 3rd generations). In particular, substitution of the CH=C(CH₃)₂ fragment in chrysanthemic acid by the CH=CHal₂ moiety increases photostability of pyrethroids. Thus, three compounds (cis-permethrin, Y, cypermethrin, Z, and deltamethrin, W) were prepared from cis-2-(2,2-dihalovinyl)-3,3-dimethylcyclopropane-1-carboxylic acid and 3-phenoxybenzaldehyde according to the scheme below.

Write down the structural formulae of S, T, W, Y, Z. Note that the halide content in W, Y, Z is 31.6, 18.1, and 17.0 %, respectively.


I got S and T and they are attached, but I can't get Y, Z and W (the halide content confuses me). I think that it is esterification of acyl chloride with alcohol. Below, in the attachment there are my guesses for Y and Z, but I can't deduce W (it needs to have a bigger halide content). What is W?

[discodermolide]

These structures look Ok.
As for the halides you will just have to run the combinations, 2 x Cl, 2 x Br, Cl, Br for weight of halide.
Chem Draw can do that for you easily.

[Rutherford]

I got a close result only for Y when replacing Hal with Cl. For others there is a bigger mistake than 4%  .
If I replace Hal with Br, for one structure I get little more than 31.6% and for the other I get little less than 31.6%.

[discodermolide]

Yes I get the same errors.

[Rutherford]

I searched the structures on the internet and found that the nitrile group -CN didn't convert to -COOH, which is hardly possible as there was an acid H⁺ in the synthesis that should've turn the nitrile group to carboxylic group. I guessed correct for Y, the two other structures are:
http://en.wikipedia.org/wiki/Cypermethrin
http://en.wikipedia.org/wiki/Deltamethrin
How could the nitrile group survive?

[discodermolide]

The acid was probably there to generate HCN which gives the cyanohydrin.
As they don't supply any reaction conditions it's difficult to say what is going on exactly. If it had said heat/NaCN/H⁺ then one could expect the CN to be hydrolysed.
The CN group is probably metabolised in the insect to the acid.
These people need to be more specific in their question formulation.

[Rutherford]

If it had said heat/NaCN/H⁺ then one could expect the CN to be hydrolysed.

There wasn't the heat, so it probably survived  .

[discodermolide]

As I said they need to be a bit more specific in giving the reaction conditions.
But wait a minute, one of the compounds is the carboxylic acid so the CN must have hydrolysed!

You moving on to the heterocyclic part now?

[Rutherford]

Which one? The two from wikkipedia are made from the nitrile (T), the one that I guessed correctly is made from S, which doesn't have a nitrile or carboxylic group.

The heterocycle problem seems very very tough, so I am not sure if I am going to attempt it soon. I thought more about the problem above.

[discodermolide]

Sorry my mistake.