Hey guys!
As Part of my master thesis I am supposed to synthesize several Pyridin-(Pincol-) Boronic-acid-esters. The synthesis of them was quite straightforward, but some time ago I ran into a few Problems and I thought I might be able to crowd-source this problem, with the hope that someone, who has experience on the topic will read my post.
My compounds are almost all oils, so recrystallization does not seem to be an option. I tried to distill my compounds, but they seem to be too heavy, or the vacuum too bad, or the Kugelrohr-apparatus not sufficiently airtight. Depending on your point of view.
But still, distillation is still my best bet, if I can get the pressure down sufficiently. The Compounds are quite pure (>90%) but for coming coupling experiments they are supposed to be as pure as possible.
Up to a few days ago I thought that a flash column is out of the question, since with standard-eluent-mixtures I was not able to produce proper, TLCs that do not smear all the way. Then I found a Paper[1] I which they try to saturate the silica with Boric acid to improve the separation. According to the authors this does not necessarily work for Pyridin-Boronic acids. Of course I tried it anyways, and was disappointed. Does anyone know solvent systems where chromatography might still be possible? I thought about reverse phase, but that is probably too expensive.
Is anybody experienced on the topic and would like to share that knowledge? I find it odd, that the whole world is Suzuki-coupling, but there apparently are no standard purification Methods, when distillation and recrystallization are not an option. Or am I just not finding them?
Well, thank you for reading this post, I would be really happy for any kind of answer.
Best regards
Skx
PS.: It might be possible to purify small amounts via Prep-HPLC, but I am to produce >1g, so this might be difficult (yet not completely impossible).
[1] Chem. Lett.
2012,
41, 972-973.