It depends which isomer of a pyrrole boronic acid you are interested in - alpha or beta. The most common methodolgy requires a lithiation of an alpha position and then reaction with i.e. trimethyl borate. The complication that has to be sorted out before starting lithiation is a reactivity of NH group which will react in the same fashion as the C-H, but more efficiently. The solution is a protection of nitrogen by a BOC group (t-butyloxycarbonyl) which is rather labile in acidic conditions but robust for basic media. In the above condtions you are obtaining a boronic acid not an ester. When we were syntesizing this compound we adapted conditions from the reference below:

S. W. Haynes, P. K. Sydor, A. E. Stanley, L. Song, G. L. Challis, Chem. Commun. 2008, 1865.

For deprotection conditions you can have a look here:

Angew. Chem. Int. Ed. 2015, 54, 1906–1909.

You can also consider running a palladium catalyzed process starting from a bromo derivative of pyrrole and pinacol borane. It also requires protection of nitrogen because of a compteting process of C-N bond formation. For some details about this approach please look here: J. Am. Chem. Soc., 2007, 129 (11), pp 3358–3366.

Hope it will be useful. Good luck with your synthesis.

Milosz.

Milosz pawlicki

Thanks a lot for your feedback

I am trying to synthesize at alpha position by first iodonation and then reaction with pincol borane

the other alpha position has ethyl ester.

I can't proceed with lithiation process as there is presence of ester group. 

The problem I am currently facing is the dehalogenation and not boronation at all. 

I will look in the articles you mentioned and get back to you if I get something positive out of it

Hydrogenation instead of borylation is a normal side product for this reaction, the way the reaction goes depends on your substrate and the Pd catalyst used. You can screen some commercial Pd catalysts to avoid it. Another route is to try bis(pinacolato)diboron instead of pinacolborane.

http://www.organic-chemistry.org/namedreactions/miyaura-borylation-reaction.shtm 

  If it is possible for you to protect the N atom, you can use I-Mg exchange, developed by Knochel, and quench with trialkylborate:

https://www.heterocycles.jp/newlibrary/downloads/PDF/23148/88/2

and references there.

Its price is 100$/gram.

I would protect the nitrogen with Boc and use iPrMgCl-LiCl at -50 °C, then quench with B(OMe)3 and add pinacol. That seems to be easier to me and has got better chance for success than the coupling.

you can use PdCl2(PPh3)2 catalyst and Bis(pinacolato)diboron in PEG solvent. The procedure gives the best results in formation of boronic ester. Go through the following reference for more details.

Lu, J.; Guan, Z.-Z.; Gao, J.-W.; Zhang, Z.-H. Appl. Organomet. Chem. 2011, 25, 537–541.

I have attached the reaction Scheme I am trying at the time. The desired product is not formed rather dehalogenated product is synthesized. I can't use lithation chemistry as there is ester.

You can easily use halogen-magnesium exchange at low temperatures, there are dozens of examples with esters. Iodine on heterocycles can be exchanged for Mg even at -60 °C, so esters are not attacked. Another variant is here, even at RT: http://www.organic-chemistry.org/abstracts/lit1/111.shtm

you did not mention what Pd catalysts did you use,  exactly we follow the Lu procedure. (Lu, J.; Guan, Z.-Z.; Gao, J.-W.; Zhang, Z.-H. Appl. Organomet. Chem. 2011, 25, 537–541). I think this procedure will work for you, I have made complicated boronic esters using this procedure.

@avula 

I used PdCl2(PPh3)2 catalyst. I tried with pinacol borane and B2(pin)2 respectively.

Did you make with pyrrole ? I have synthesized pyrrole aldehyde boronic acid using lithation chemistry but I am unable to prepare the above mentioned pyrrole. 

you would try to convert the pyrrole boronic acid into ester simply by mixing the pyrroly boronic acid(with N-protected) that you synthesised through llithiation or Grignard reaction with pinacol in dry ether, it would be purified by column.