Cyrax (Hive Bee)
10-03-02 00:14
No 363414
      alpha-ethylstyrene synthesis (organometalic chem.)  Bookmark   

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 čta-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?
(Chief Bee)
10-03-02 00:19
No 363416
      Wittig gets my vote  Bookmark   

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
(Hive Bee)
10-03-02 01:07
No 363432
      Oeps, forgot to tell: Cp = cyclopentadienide Yup ...  Bookmark   

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. frown
(Hive Bee)
10-04-02 01:19
No 363917
      phenyl-2-propanone  Bookmark   

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.
(Chief Bee)
10-04-02 02:25
No 363957
(Rated as: excellent)

Here are references related to the synthesis of alpha-ethylstyrene:

../rhodium/pdf /alpha-ethylstyrene-1.pdf
../rhodium/pdf /alpha-ethylstyrene-2.pdf
../rhodium/pdf /alpha-ethylstyrene-3.pdf
../rhodium/pdf /alpha-ethylstyrene-4.pdf

Regarding your Tebbe/phenylacetate idea, there is a similar synthesis at my page: ../rhodium/chemistry /phenylacetone.html#ylide
I don't know if the Tebbe works on esters, but if it does, then the hydrolysis would work like a charm.