[Mpatas]

Hello guys,

I tried today to make this compound starting from 6-bromo-2-methyl pyridine by using n-buLi and tributyl tin chloride. Unfortunately  my product is not pure. Is it possible that n-Buli deprotonated the methyl group and i got substitution of tributyltin on the methyl group? Because my proton NMR indicates a twice the number of the proton that i need to have.

[TheUnassuming]

Possible perhaps, but not likely no.  More likely is that you have tin impurities that are showing up in your NMR.  Tin is notorious for streaking all over a column, making purification a bit more tricky.
Now when you say you have twice the number of protons, do you mean you have twice the number of tributyltin protons?  Do you see fewer methyl protons than you would expect relative to the benzyl protons?

[Mpatas]

So when i integrate my spectra i have 57 protons instead of 27 and i also have additional peaks in the aromatic region. One pick that it really makes me wonder is a doublet at 8.4. I did a column and i couldn't purified it. The literature suggests vacuum distillation.

[Mpatas]

I see more methyl protons

[TheUnassuming]

Ok. So try a few things to figure out what is going on:
First, get an NMR of your SnBu3Cl and make sure its clean to start (double check the purity of your starting material as well).   
Next, repeat your lithium halogen exchange reaction, but this time quench with D2O and get an NMR/mass of the product.  If you get a deuterium where your Br used to be and nothing else, then you know the Li-X reaction is going well and its the last step of the reaction causing problems.   
If thats the case why don't you try the suzuki coupling route instead of the stille coupling?  The boronic acids are much easier to make/purify, are less toxic, and the actual coupling in the next step has always worked in higher yields for me.

[Mpatas]

Thanks for you ideas. I will definitely try out a few of them