I'm trying to do a reaction with phenyl piperazine, triphosgene, and 4-bromophenol. However, every time I do this reaction I seem to get the carbonyl di-4-phenylpiperazine as a major product (based on the LCMS masses). I tried to reduce the triphosgene step to 5min, which seemed to yield trace amounts of the intended product, but I still can't get my intended product as the major product. Going by the TLC, it even looks like the starting materials were not consumed (SM1 = phenyl piperazine, SM2 = 4-bromophenol, R = reaction mixture). This should be such a simple reaction - what am I doing wrong?