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Why won't this simple reaction work?

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Spezialemic:
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?

rolnor:
You should mix the triphosgene and bromophenol first, to get the chloroformate, then add the piperazine. You can use carbonyldiimidazole instead of triphosghene but then you need to heat, say 70°C in THF. I love that you post the TLC!

wildfyr:

--- Quote from: rolnor on July 12, 2019, 06:31:18 PM ---I love that you post the TLC!

--- End quote ---

OP is the hero we need. And I agree with Rolnor's suggested addition order.

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