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[tjanne]

Hi, Im trying to synthesize hypervalent diarylidoniumsalts, Ar1-(I+)-Ar2, using iodoarenes as Ar1 and arenes as Ar2.
To oxidize the iodoarene I use mCPBA and TfOH (triclic acid) is added to act as counterion. Up until this point everything works great. When I add Ar2 however, it becomes a black tar. It works "ok" when employing benzene as Ar2 but if I try for example anisole it´s just a mess. I can detect product but it´s mixed with this inseparable black stuff. I suspect some sort of oxidation of Ar2 due to harsh conditions (the same black precipitate forms by mixing only Ar2 with mCPBA and TfOH). I have tried different addition orders, and slow addition at -78 degrees celsius etc.
I cant really figure out what this black stuff is even though I´ve tried running GCMS and NMR 
Could anyone here help me figure out what happens to the anisole? Is anisole much more prone to oxidation than benzene?
Thanks!

[discodermolide]

Anisole is very prevalent to oxidation due to the methoxy group. It may be worthwhile trying a weaker acid than triflic acid. Acetic perhaps.

[tjanne]

Anisole is very prevalent to oxidation due to the methoxy group. It may be worthwhile trying a weaker acid than triflic acid. Acetic perhaps.

Thanks for the reply, I´ve tried a couple of weaker acids as well (Acetic, TsOH, mCBA for example). Unfortunately, the less aggressive acids gives little or no final product on Aryliodides with EWG-substituents.
Would be fantastic if I could get it to work with another acid since I could easily just make a counterion exchange with TfOH at a later stage. Any suggestions on other acids to try out?

[discodermolide]

Well I would not call the methoxy group attached to a benzene ring an EWG, it pumps electrons in making it quite a reactive molecule.
As for other acids, mCBA, I presume you mean meta-chloroperbenzoic acid, is an oxidant not an acid.
Try going up a series of acids like chloro acetic, dichloro acetic etc. Or the fluoroacetic acids.

[tjanne]

Well I would not call the methoxy group attached to a benzene ring an EWG, it pumps electrons in making it quite a reactive molecule.
As for other acids, mCBA, I presume you mean meta-chloroperbenzoic acid, is an oxidant not an acid.
Try going up a series of acids like chloro acetic, dichloro acetic etc. Or the fluoroacetic acids.

Nah, i mean the other part of the iodoniumsalt, the aryliodide (Ar1-I). On that side I have EWG substituents. Ar2-OMe is of course donating. With mCBA I mean meta-chlorobenzoic acid, not the corresponding peracid (mCPBA).
Ah, good advice. I think I'll try that series tomorrow. Thanks =)