I react phenylacetylene with 3-iodoaniline via Sonogashira cross coupling but But I got a second spot on TLC it probably due to the Buchwald-Hartwig reaction What should I do in order to I overcome this problem?
I think reacting the amino group with a sterically hindered protecting group, e.g. Boc, Fmoc or 4-Methoxybenzyl might favour the Sonogashira over the Buchwald-Hartwig coupling. Especially the Fmoc group should be able to easily be dprotected with piperidine. Also at least one spot may occur due to Glaser-coupling of the acetylene if there's some oxygen present. Also I think I saw one spot in one of my Sonogashira-couplings due to dissociated phosphane ligand. Have you tried to analyze the second spot?
dear Lukas Holz, thanks for participating I carry out the reaction under nitrogen so homo-coupling we can exclud it. I shall analyze it after separation.
You're welcome. I have a question though: which precatalyst did you use for the Sonogashira coupling? Palladium(0) or a palladium(II) salt? If I recall correctly I used [Cl2(PPh3)2Pd] as precatalyst which, during activation to form the Pd(0) species, may also have been a viable oxidant for the Glaser coupling. Although the hypothesis of diphenylbutadiyne being formed may easily be discarded by running a TLC with your product and diphenylbutadiyne.
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