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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: JUI on July 22, 2011, 06:47:40 AM

Title: epoxide ring opening
Post by: JUI on July 22, 2011, 06:47:40 AM

 Hi ,
 
 ( My English might be wrong. I am so sorry ! )

 I'm trying to open epoxide ring with deprotonated TMS-acetylene ( with n-BuLi ).

 My starting material is TBS-protected glycidol.

 I tried BF3.OEt2 as the acid catalyst at first but it didn't work.

 On TLC, most of starting materical did not react and just stayed.

 and I got some TBS-deprotected compound.

 I think BF3.OEt2 is not enough to open the epoxide, but I am not sure.

 Because I read the paper doing the exact same experiment and it said BF3.OEt2 did work.

 Maybe I did something wrong but I can't find why.

 Now I am trying HMPA and It works but the yield is very very low

 and I got TBS-deprotected compound again.

 can anybody give me some advice ?

 I am so sorry for my bad English, again.

Title: Re: epoxide ring opening
Post by: opsomath on July 22, 2011, 09:42:16 AM

Can you clarify some things?

1) Why are you using the BF3 complex? It seems to me that lithium TMS-acetylide should be able to ring-open an epoxide by itself.

2) I had a similar situation where I was trying to substitue Li-TMS acetylide onto a primary alkyl halide. It didn't work at all in THF or ether, I had to use HMPA, same as what you are seeing.

3) If the protecting group is really a problem, you can use epichlorohydrin or bromohydrin. The product should be the epoxide-substituted TMS, and you can ring-open gently and protect for the next step.

What is the paper you are going off  of?

Title: Re: epoxide ring opening
Post by: Doc Oc on July 22, 2011, 10:31:03 AM

How old is the glycidol?  I've used that stuff before and it does slowly hydrolyze on its own.