[Sergio]

Hello !

I'm desperately trying to achieve that reaction described on the reactional scheme, with the best selectivity on alkyl chains. (my latest synthetic chemistry lesson is 25 y.o. yet)

-R' is anything but -H, atom bonded to aromatic cycle is mandatory carbon
-R and R'' are just linear alkyl chains

Anyone kind enough to help me a bit ?

[rolnor]

I dont understand, do you want to change the whole chain or make changes in the chain?

[Meter]

Maybe you could activate the alkyl chains with something like chromic acid?

[rolnor]

If the sidechain is methyl, you can oxidize to COOH, then make a Curtius rearangement with DPPA/TEA to get the NH2, then diazotise and reduce the diazonium salt with phosphoric acid to hydrogen. Then, somehow, you can introduce another alkyl chain. You need to protect the free OHś with a protection group, othervise they get oxidized. This method is bad and wont work but is somekind of a startingpoint. When you have the OH-s you can not use Friedel Craft to introduce the new sidechain, it will be in the o-position, not the m-position that you want.

[Meter]

If the sidechain is methyl, you can oxidize to COOH, then make a Curtius rearangement with DPPA/TEA to get the NH2, then diazotise and reduce the diazonium salt with phosphoric acid to hydrogen. Then, somehow, you can introduce another alkyl chain. You need to protect the free OHś with a protection group, othervise they get oxidized. This method is bad and wont work but is somekind of a startingpoint. When you have the OH-s you can not use Friedel Craft to introduce the new sidechain, it will be in the o-position, not the m-position that you want.

Won't any alkyl chain be oxidized to COOH? That's what my textbook says.

[Meter]

Or maybe use radical substitution (Cl₂ or Br₂ over UV or heat) and react with an alkyne followed by catalytic hydrogenation. Obviously not great either.

[rolnor]

If the sidechain is methyl, you can oxidize to COOH, then make a Curtius rearangement with DPPA/TEA to get the NH2, then diazotise and reduce the diazonium salt with phosphoric acid to hydrogen. Then, somehow, you can introduce another alkyl chain. You need to protect the free OHś with a protection group, othervise they get oxidized. This method is bad and wont work but is somekind of a startingpoint. When you have the OH-s you can not use Friedel Craft to introduce the new sidechain, it will be in the o-position, not the m-position that you want.

Won't any alkyl chain be oxidized to COOH? That's what my textbook says.

I think it depends on the conditions.

You can block the o-positions by bromination, make a allyl ether of one or both OH-s, then make a Claisen rearangement to get a allylgroup in the vacant position, then cleave the allyl ether/ethers with HCl (aq) and oxidize the allyl group to aldehyde by OsO4/NaIO4. This aldehyde can be transformed to many alkyl groups by Wittig etc. Then hydrogenate the bromo-s.

[Sergio]

I dont understand, do you want to change the whole chain or make changes in the chain?

Thank you for your reply.
I want to change it. Starting with a propyl or pentyl  group and replace it with heptyl, for example...

[Sergio]

Thank you all for your interest, hints and ideas. I'm really grateful !
I will study them (need some time !) and let you know if I manage to do something out of them...

P.S: -R and -R'' are at least 3 C long. No methyl nor ethyl !

[rolnor]

If you start with aldehyde, you can make all other chains from this by Wittig.