I'm trying to brominate pyrrole at the 2 position using AIBN and DBDMH and put a T-boc on the pyrrole nitrogen in situ. The Org Synth prep says to filter the 2-bromopyrrole solution, which is at -78 C, into a new flask which is also cooled to -78. To this solution you add the reagents to install the tboc. I tried filtering with a cannula having filter paper secured on one end, but I got a bunch of what looks to the tribrominated product. I think i let it get too warm in the transfer.
Does anyone know a way to filter a cold solution under inert conditions? I am trying to find something on it in my lab techniques book but there doesn't seem to be any well known ways of doing it.