[Embark04]

Hi guys/ladies:

Some time ago I made a post about having difficulties with a Grignard reaction using vinylmagnesium bromide. A couple of you (I want to thank, but I forget exactly whom it was) suggested making my own and running the reaction again. Well, I can now tell you this was a complete success. Making the vinylmagnesium bromide was not fun, but well worth the effort. The reaction was complete at -78 C within 10 min (as opposed to 1h at 25 C with Grignard from Aldrich). However, my yield only improved slightly. I am now concerned that the previous step, that of synthesizing the aldehyde substrate via oxidation of a 1,2-diol by NaIO4 may be an issue.

The problem is, the aldehyde is very volatile, and susceptible to decomposition on a silica column. I usually separate the org layer of the reaction and dry with MgSO4, remove solvents, then use immediately in the next step (vinylation). My question is then, is there another good way of oxidizing the diol to the aldehyde via another method other than Pb(OAc)4 or Na periodate....I cannot be sure if this is even the problem. The paper I got the procedure from claims a 80% yield over these two steps I am writing about to you now. I am starting to believe the yield is BS and inflated (surprise). I follow the protocol to a T. Just not working as described.

I know this isn't too much details, but if anyone can see some problem, or has experienced similar problems with this type of chemistry (the oxidation, etc) the advice is appreciated.

Thanks.

[azmanam]

I've made 3-butenal by oxidative cleavage of the corresponding symmetrical diol using NaIO₄ before.  This aldehyde's volatile and susceptible to isomerization to the conjugated enal.  Reaction works as described in this paper.  Only change to my procedure, was I didn't purify the aldehyde product by distillation.  I washed with water, then stirred the DCM solution over sodium sulfate until I was ready to use the aldehyde.  Then I cannulated the aldehyde/DCM solution into my reaction flask and continued with the reaction (I was using the aldehyde as an electrophile in an aldol addition).  In my hands, I got an 80% yield, >20:1 dr for my enantioselective aldol using this freshly-cleaved aldehyde in my reaction.