alpha-ethylstyrene synthesis (organometalic chem.)

Cyrax · October 03, 2002, 12:14:00 AM

I wondered about what would be the most convenient method to make 2-phenyl-1-butene?
This may seem somewhat exotic, but I thought about starting from propiophenone and reacting it with the Tebbe reagens (an èta-2 carbene, that reacts pretty much the same way as the Wittig reagens, with the only difference that it also reacts with esters).

The ordinary way to make it is:

Cp₂TiCl₂ + 2 AlMe₃ --> Cp₂TiMe₂ + 2 AlMe₂Cl
Cp₂TiMe₂ --> Cp₂Ti=CH₂ + CH₄

An improved way to make it is:
Cp₂TiCl₂ + 2 MeLi --> Cp₂TiMe₂ --> Cp₂Ti=CH₂

The Cp₂Ti=CH₂ reacts consequently with the propiophenone in a concerted way (forming a 4 membered ring) with as products the alkene and Cp₂Ti=O

Or mabey a Wittig reaction would be more simple? What do you think about it?

Rhodium · October 03, 2002, 12:19:00 AM

Without a question, I'd say a Wittig reaction would be the answer here.

PPh₃ + MeI -> MeP⁺Ph₃

MeP⁺Ph₃I^- + KOtBu -> CH2=PPh₃ + KI + t-BuOH

CH2=PPh₃ + Propiophenone -> alpha-Ethylstyrene + O=PPh₃

Cyrax · October 03, 2002, 01:07:00 AM

Oeps, forgot to tell:
Cp = cyclopentadienide

Yup Rhodium, the Wittig would probably be better. The starting product for the Tebbe reaction are rather peculiar, one needs to prepare MeLi, and the reaction is normally done in toluene-THF containing a small amount of pyridine (which I guess is watched). I don't know about it, but I think the Cp₂TiCl₂ would not exactly be cheap.

A method to form the Tebbe reagent in situ can be found at J. Org. Chem. (1985) vol 50 p 2386. Mabey I 'll check it out once - as a chemistry curiosity -, but it's not on my priority list right now.

So many things to do, so little time.

Cyrax · October 04, 2002, 01:19:00 AM

I 've got another idea about the application of the Tebbe reagens. It concerns the synthesis of phenyl-2-propanone.

Follow me on this one:
* Benzylcyanide --> Ethyl phenylacetate (Alcoholysis: 86 %)
* Then, we would perform the Tebbe reaction on Ethyl phenylacetate, hereby replacing the oxigen wit a methylene group.
* This yields an enol ether. And, if my memory serves me right, enol ether can be hydrolised (I think by refluxing it with an aqueous HCl solution). Can someone confirm this? Or is my memory playing tricks on me?

What do you think about this synthesis? If it sounds good, I 'll try to work it out in a seperate thread.