Perbenzylated cyclodextrins

DIBAL (150 eq.), PhCH, 50°C, 2 h, 82% yield, perbenzylated cyclodextrin as substrate. The method is also applicable to the monodebenzylation of perbenzylated mono and disaccharides.DIBAL in combination with triiso-butylaluminum has also been used successfully to cleave benzyl groups from carbohydrates. ... 

Debenzylation. Perbenzylated cyclodextrins (a-, P-, and y-forms) are partially debenzylated by Dibal-H in toluene in a regioselective manner to provide the mono-6-O-debenzylated or AD-di-0,(9-debenzylated derivative. 

We first describe a synthesis of alpha cyclodextrin. The synthetic plan is shown in Scheme 1. An immediate precxirsor for 1 could be the perbenzylated precursor 5, which could be cleaved to give a linear glucohexaosyl fluoride 6. This key intermediate 6 is obtainable from the maltose derivatives 8 and 9 through the intermediacy of the glucohexaose derivative 7 ... 

Another way to perfunctionalize cyclodextrins is to use the difference of reactivity of each position toward deprotection. Perbenzylated a-cyclodextrin 10a is obtained quantitatively using benzyl chloride and sodium hydride in anhydrous DMSO [18]. 

The selective de-O-benzylation of perbenzylated a-cyclodextrin can go further if different reaction conditions are used [66]. Using more equivalents of DIBAL-H, different solvents, and a longer reaction time, tri- and tetrafunctionaHzed a-cyclodextrins 65 and 66 can be obtained in reasonable yields (Scheme 9.32). To... 

Applying the same conditions as mentioned earlier to perbenzylated P-cyclodextrin 10b also resulted in further de-O-benzylations [67], but only on the primary rim (Scheme 9.33). This gave access to two trifunctionalized fS-cyclodextrins 67 and 68 and a tetrafunctionalized one 69 in moderate yields. The observed regioselectivity is also justified by the stepwise successive de-O-benzylations. The positions 6A and 6D would be the first to react, and then an aluminum derivative would be chelated between the hydroxylate formed and the... 

Double Deprotection of Perbenzylated oc- or -Cyclodextrins Using DIBAL-H... 

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