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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: matman27 on September 09, 2011, 08:45:00 PM

Title: Vinylalumination to beta-substituted olefins
Post by: matman27 on September 09, 2011, 08:45:00 PM

Hello Fellow Chemists,

I am in the process of trying vinylalumination on a methyl propiolate to generate a beta substituted vinyl compound.  I am following the procedure of Ramachandran (J. Org. Chem. 2003, 68, 9310-9316), so I can use NMO instead of HMPA.  They are able to produce beta substituted olefins with phenyl and methyl groups; I am trying isopropyl.  It seems that my reagent may not be getting generated properly because I still see some precipitate after adding the DIBAL-H to the NMO, and my propiolate is still visible on TLC after many hours.  Could my problem be with the quality of my NMO?  I put it on the vacuum for about an hour before I use it because I am afraid moisture is present from being stored in the freezer.  Otherwise, could my issue be sterics?

Thank You,

-Matt

Title: Re: Vinylalumination to beta-substituted olefins
Post by: OC pro on September 10, 2011, 02:42:30 PM

Have never heard of NMO as substitute for HMPA. Did you mean DMPU?
http://en.wikipedia.org/wiki/Hexamethylphosphoramide#Alternative_reagents
With NMO it will not work.

Title: Re: Vinylalumination to beta-substituted olefins
Post by: Honclbrif on September 10, 2011, 03:11:25 PM

Looks like they're using the NMO as a complexing agent for the aluminum species, not as a solvent (mp = 180°C). However, I am a little surprised it doesn't just oxidize the DIBAL, but there's apparently precedent for this sort of thing.

Anyway, sounds like your initiation isn't working. Look at all your reagents and solvents. Is your THF dry? Have your NMO, DIBAL, or propiolate decomposed or become contaminated? Are you rigorously excluding water and oxygen? If those are all good, you could try trapping with an electrophile from the paper. If that works but your substrate doesn't, than this pathway might not be one you can use.

Title: Re: Vinylalumination to beta-substituted olefins
Post by: Doc Oc on September 11, 2011, 08:00:34 PM

I've tried this vinylalumination and so have several of my colleagues and none of us could get it to work, it's a crap reaction.  Try a Baylis-Hillman reaction with MgI₂ to get the B-iodoacrylate, then cross couple that to get the isopropyl compound.  That reaction has been reported and I was able to achieve similar compounds in high yield.

Title: Re: Vinylalumination to beta-substituted olefins
Post by: matman27 on September 12, 2011, 12:11:03 PM

Thank You for the replies.  I will go through the B-iodoacrylate.  -Matt