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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: Mark on June 26, 2007, 10:13:00 PM

Title: Dianionic Claisen
Post by: Mark on June 26, 2007, 10:13:00 PM

Anyone have advice for doing a dianionic claisen rearrangement? I've tried LiHMDS in THF at -78 to form the chelate and enolate, then reflux for >12hrs. Most of the starting material doesn't react and the small amount that does react just splits my ester back to an acid and alcohol. Solvents are dry, reagents are dry, flasks are dry.....is there some trick I'm missing? 

Title: Re: Dianionic Claisen
Post by: kiwi on June 29, 2007, 02:04:33 AM

not familar with that one - is it something like the Ireland-Claisen rearrangement?

http://www.organic-chemistry.org/namedreactions/ireland-claisen-rearrangement.shtm

Title: Re: Dianionic Claisen
Post by: Mark on June 29, 2007, 11:11:53 AM

It's similar but there's a beta hyroxy group which helps out the selectivity. It's been done by Kurth in the 1980s.

Title: Re: Dianionic Claisen
Post by: kiwi on July 01, 2007, 07:22:06 PM

ah ok, have you tried other bases? those HMDS bases seem to not store well in my experience, some freshly generated LDA might do the trick.

Title: Re: Dianionic Claisen
Post by: Mark on July 04, 2007, 01:51:36 PM

I generate the LiHMDS fresh each time I run the reaction rather than buy it. But switching to LDA is worth a shot.