Alkylation of Acetylacetone (pls help)

[Guest yessipermana]

Please help...

 

I've been working on alkylating acetylacetone (2,4-pentanedione or Acac) with isopropyl alcohol by means of BF3 for 2 months, but resulting in nothing.

 

I have tried once with my solid zirconium lewis acid catalyst which is good for esterification (almost general) and alcoholysis (specific), but it was also unsuccessful.

 

Well, basically, I just want to get alkylated acetylacetone, substituting one proton situated in its methylene site. It is just fine to get it alkylated by any alkyl. If possible to alkylate it with halide-alkyl, it would be so great.

 

If I'm not mistaken, the alkylation of a substance, like Acac, could be carried out by first creating carbanion in Acac and then attacking the carbanion by carbocation from isopropyl (after releasing the -OH group).

The process is supposed to be possible by the use of conventional lewis acid (organic synthesis reagent), such as BF3, AlCl3 and other type of conventional lewis acid catalysts.

 

I carried out the reaction at low temp ( 0 deg C) to avoid deactivation of BF3. (actually I use BF3-OEt2 or diethylether stabilized boron trifluoride, but it should posses exactly the same activity as gas BF3).

 

Could anyone help me...

 

Thanks a lot...

 

yessi

[blike]

Hrm... I'm not sure off the top of my head, but I think your best bet would be to create the carbanion and carbocation. I'll need to look at it a bit. Any alkyl chain at either of the methylene sites right?

[wolfson]

Why not try 3-cinnamalidene-acetylacetone?

[Guest yessipermana]

Blike, yea, any alkyl chain at either proton of the methylene site. actually I tried also the alkylation of benzoylacetone (1-phenyl-1,3-butanedione), which has one phenyl group (substituting one methyl group). I thought it was successful because I saw physical changes (color and viscosity) of the solution. But I was surprised to see the 1H-NMR result. It's just exactly still a benzoylacetone (although physically it has changed).

I was also thinking of alkylating it with tert-butanol, since it posseses tert-carbocation after releasing -OH group, which is more stable than sec-carbocation of isopropyl group.

What I confused now is where actually the mistake is. The lewis acid reagent or the alcohol?

 

Wolfson, I don't get the substance with that name. Would you specify the IUPAC name for me. Just now I checked the structure with ChemDraw to see what "3-cinnamalidene-acetylacetone" you suggested is, but no such structure is available. Really need your help.

[chemistry]

Use PBR3 to convert the alcohol to an akyl halide.

 

Use a moderately strong base to deprotonate the central activated hydrogen (methylene). You don't want the base to react with either of the carbonyl groups.

 

The alkyl halide and the resonance stabilized enolate compound (the deprotonated dicarbonyl compound) will react by SN2 reaction and you will have your product.