Synthesis help!

[stonedcarli]

I have a question about this synthesis problem. I am unable to find a way to solve this.

 

 

2 Benzyl Bromide -> trans-1,2 diphenylethylene

 

 

Hope the picture works

 

This is in the chapter of Alcohols from a introductory organic chemistry book.

There seems to be no limit into what reagents I am allowed to use but I'm sure most of it will be Orgo 1 reagents (grignard, E1, E2, dehydrogenation)

Edited January 20, 2010 by stonedcarli

[BrainWasher]

I wonder if a strong acid could react with the bromine resulting in a covalent bond between the two benzyl groups.

 

I'm not too sure. I figure I would present the simplest thought first.

 

Otherwise, I would recommend digging into Grignard Reagent reactions. That seems to always be the most versatile organic synthesis tool. As soon as I can get to my Schaumm's Outlines I will look it up.

 

I really need to look into Grignard Reagents again.

[Mr Skeptic]

Are you familiar with a reaction between a terminal bromide and a terminal triple bonded carbon?

[stonedcarli]

Yes I am aware of it. If I remember correctly a terminal alkyne can be reacted with a NaNH2 and become a carbene. This carbene can then displace an alkyl halide by Sn2 substitution.

 

However I don't see how this could work in a lab situation..

 

1) React the alkyne with NaNH2

2) distill the conjugate base.

3) pour it into our orginial sample?

[Mr Skeptic]

Well, this forms a carbon-carbon bond, no? So what reagent would you need to react with what you are given, so that it would result in your target molecule? There's your answer.

[Syntho-sis]

You called?

 

(Sorry couldn't resist it.)

[stonedcarli]

 

Clearly it's not working, is my mechanism wrong?

[Mr Skeptic]

Your other reagent is too big.

[UC]

*cough cough* triphenylphosphine. Go from there.

[stonedcarli]

I'm not sure how to use triphenylbenzene, I was never taught it's reaction before.

 

If I used BromoBenzene I would get the target compound but wouldn't it defeat the purpose of the 2 moles of benzyl bromide?

 

If anyone can explain how PPh3 works with this reaction, I'd greatly appreciate it.

[Mr Skeptic]

If I used BromoBenzene I would get the target compound but wouldn't it defeat the purpose of the 2 moles of benzyl bromide?

 

Yeah, they do a lot of stupid things for homework questions. What's important is that you are able to figure out how to make one, and the easiest solution is the best for that purpose, even if it is a dumb reaction in real life. Methinks you're overthinking this one.

[stonedcarli]

Well, thank you all for your help. I guess it's case closed for this problem.

[ChemSiddiqui]

for future reference grignard reagents usually are used if a carbon-carbon bond formation is involved, but of course the conditions are important in choice of reagents!

[akcapr]

the reaction you drew works as far as i can tell. i dont see another viable synthetic approach based on your level of ochem.

Edited January 27, 2010 by akcapr