[RaInBowDaSh1488]

Recently, I've been trying to synthesize 3-bromo-2-formylthiophene. This seemed super straightforward, but I've managed to run into a wall  . Using 3,4-bromothiophene and 1.1 eqv BuLi, I end up getting multiple formylation products. I am getting primarily the desired product, but also formylation at both bromines and an unknown impurity. I think the unknown is a result of some other dibromothiophene isomers in the starting material. In the course of the reaction, all of the starting material is consumed, I just get a mess that is not possible to purify satisfactorily.

My question is, would LDA possibly give better results or is it likely that both LDA and BuLi will lithiate at either the 2 or 3 bromine with little discrimination? My thinking is that with LDA I might at least be able to get around the double formylation. Does this seem reasonable?

[opsomath]

What is the temperature at which you're reacting? Also, have you tried using magnesium-halogen exchange with iPrMgCl instead? That should be a very mild and clean conversion.

[RaInBowDaSh1488]

What is the temperature at which you're reacting? Also, have you tried using magnesium-halogen exchange with iPrMgCl instead? That should be a very mild and clean conversion.

The temperature was ~ -70 °C but allowed to heat to rt after about 1.5 hr. The magnesium halogen exchange does sound like a good idea actually and I will absolutely look into it. I'm just wondering how selective it would be considering there are halogens on the starting material.

[opsomath]

It should be possible to be selective; the 2-position is much more reactive. I found this:

http://www.ncbi.nlm.nih.gov/pubmed/14629185

[NiceWeatherSunshine]

How concentrated are you running this reaction? Solvent?