[Aurelien]

Hi there,

I am trying to prepare the 6-O Tosyl derivative from beta-cyclodextrin.
There was a nice setup described by Zhong and Bittman in 1998 (Tetrahedron Letters 39 (1998) 2919-2920). I have it if you want to give it a read. This paper was cited almost 100 times...
It is interesting because they use Ts2O (the anhydride) claiming the CD forms an inclusion complex with it prior to the start of the reaction by adding NaOH (for just 10 min) and then the addition of NH4Cl (to pH=pKa) promotes the precipitation of huge amounts (9.0 g) of the exepected product.
The point is this reaction already has been pointed out as not giving pure product (I am OK with that) but in my case NOTHING precipitates.
I was wondering if maybe I should concentrate even more the reaction mixture to obtain the precipitate but on one hand it is already fairly concentrated (11 g CD, 5 g NaOH, 13.4g NH4Cl in 300 ml) and on the other hand I am a bit concerned if heating on rotavap could simply destroy my tosylate.
I am on run 3 and a bit worried. THANKS ! (PS: I lack characterisation techniques in my lab)

[kriggy]

Did you cool it overnight as is described in the procedure?

[Aurelien]

Did you cool it overnight as is described in the procedure?

well yes, an extremly small amount of unpure product precipitated after 3 days at 0-4ºC.
There was definitively a problem with the protocol because with a more standard TsCl protocol the expected Tosul derivative precipitated in large quantity at RT.
My only "logical" guess is that the described protocol suffers from commercial Ts2O. Because every people reporting this reaction claim they prepare Ts2O from TsCl and TsOH while I bought a 97% Ts2O (ACROS) and it fails me thrice.

[kriggy]

Yeah that could be the reason. Im not sure how stable it is but its probably very moisture sensitive?