[phth]

What about starting with 1-butene, making the bromohydrin with NBS in aqueous DMSO, then oxidizing the alcohol to a ketone?  Offhand, I don't have an oxidant picked out.

This. 1-butene>1,2-epoxybutane>swern oxidation with catalytic MeOH will generate the desired product in one step with decent yield and far less side products.

[Babcock_Hall]

phth,  That looks very interesting.  Is the difference between chlorine and bromine a trivial one?

[AromaticAcrobatic]

Phth,
This looks/sounds like a pretty cool reaction, unfortunately I have never heard of it until now. Do you have any other literature I can read about it or can you post the link to that paper the picture is from? So I can read more about it?

 

[rwiew]

Phth,

Cool reaction, but you're getting halogenation on the more substituted side, which is not what we wanted to do here, no?

[phth]

Babcock Hall: I believe it is a trivial difference, and oxalyl chloride is more stable, so more widely used. I read that reaction from the book called 'Oxidaiton of Alcohols to Aldehydes and Ketones' (http://link.springer.com/book/10.1007%2Fb135954).  The paper referenced is (http://www.sciencedirect.com/science/article/pii/004040209401111C) DOI:10.1016/0040-4020(94)01111-C.  I haven't had a chance to read through the paper because I'm not at the university today.  Rwiew: I doubt the reaction is extremely regioselective, but I think there will be more opening at the less substituted side which we want.  My reasoning behind the result is that the tertiary SN1 transition state requires less energy than the secondary SN2/1 transition state does, and the substituted side leads to a alcohol that cant oxidize.

[zsinger]

Def. use some kind of hindered base to afford a Hoffman product intermediate.
            -Zack

[orgopete]

Def. use some kind of hindered base to afford a Hoffman product intermediate.
            -Zack

Huh? It is an acid catalyzed epoxide opening followed by a DMSO oxidation (Swern in this case). The triethylamine is to make the sulfur ylide.

[rwiew]

Def. use some kind of hindered base to afford a Hoffman product intermediate.
            -Zack

Huh? It is an acid catalyzed epoxide opening followed by a DMSO oxidation (Swern in this case). The triethylamine is to make the sulfur ylide.

Where is that acid coming from if you're working in triethylamine? I'd say the epoxide is most likely not protonated when opened. What I think Zack is saying is using a hindered base to first attack at the less substituted end and then be displaced by the halide - there's no room for a mention of Hoffmann though, this is not an elimination.

I still don't see how this is better than brominating a silyl ether though, especially with the lack of regioselectivity.

[orgopete]

Where is that acid coming from if you're working in triethylamine? I'd say the epoxide is most likely not protonated when opened. What I think Zack is saying is using a hindered base to first attack at the less substituted end and then be displaced by the halide - there's no room for a mention of Hoffmann though, this is not an elimination.

I still don't see how this is better than brominating a silyl ether though, especially with the lack of regioselectivity.

The experiment shows phosgene plus methanol, which should give some HCl and open the epoxide. The alcohol in the presence of the sulfonium salt should give a new sulfonium salt (the ylide precursor) and HCl. So this part of the reaction can be catalytic in HCl. After all of this occurs, the triethylamine is added.

If the reaction is run from an epoxide, I agree acid catalyzed opening of an epoxide should give the wrong isomer.

This same procedure can be run directly on 1-butene by doing the bromination in DMSO, but I didn't look up the reference. That is simply an alternative one pot bromohydrin formation and oxidation. I don't know it is necessarily better than doing it in two steps, or a one step bromohydrin from 1-butyne to the product. This should give the desired regions electricity.

Re: bromination of silly enol either
I'm sure that is a fine method. If this is from air, fire, and water problem, then I don't know which is going to be better, a priori. For the purpose of the original poster's question, probably all of the answers are useful chemistry.

[zsinger]

Sorry….misread post….disregard my invalid comments.  THEY ARE WRONG
       -Z

[orgopete]

Sorry….misread post….disregard my invalid comments.  THEY ARE WRONG
       -Z

Been there, done that too many times!