Unexpected regioselective debenzylation leading to modification of both rims of α-cyclodextrin

Diisobutylaluminium Hydride (DIBAL‐H) Promoted Secondary Rim Regioselective Demethylations of Permethylated β‐Cyclodextrin: A Mechanistic Proposal

“…These remarkable results appear to be in sharp contrast to the case of benzylated CDs in which debenzylation occurs on the primary rim of the CD and on two diametrically opposed sugar rings. Furthermore, we showed that such a bis-debenzylation reaction was a stepwise process because we could isolate alcohol 2 and resubmit it to the action of DIBAL-H to obtain diol 1 [5][6][7] (Scheme 1). In the case of permethylated CDs, and in spite of our efforts, we were unable to isolate a mono-alcohol on the secondary rim, which suggests a subtly different mechanism.…”

“…cessfully applied to benzylated sugars and CDs, [4,5] allowing access to polyhetero-functionalized CDs containing two, three or even four different functionalities [5][6][7] (Scheme 1). This approach allowed us to synthesize complex CD dimers used as supramolecular cross-linkers of biopolymers.…”

Diisobutylaluminum Hydride Mediated Regioselective O Desilylations: Access to Multisubstituted Cyclodextrins

“…For example, in the cases of α/β CDs, only benzyl group(s) attached to O6 positions of the A and D units (see Scheme for labeling of a CD) are affected. We later found that this methodology could also be used to synthesize triply and quadruply O‐debenzylated products in gram quantities 4b,c. A downside of the methodology is that a large excess (>30 equiv) of DIBAL‐H is required.…”

Efficient regioselective O3-monodesilylation by hydrochloric acid in cyclodextrins

“…27e29 a,a-Dibromo-o-xylylene can also be regioselectively introduced to O2 and O3 of one glucose unit of CDs 30,31 to form O2,O3-capped derivatives (28e33% yields), and the o-xylylene can be advantageously removed by hydrogenation. More recently, diisobutylaluminum hydride (DIBAL-H) has been shown to reductively remove either methyl groups from both O2 and O3 positions of per-O-methylated CDs 32 or benzyl groups from per-2,3,6-O-benzylated a-CD; 33 in the latter case, the benzyl groups were removed in a sequential fashion to form 3 A ,6 A ,6 D -tri-O-debenzylated a-CD derivative. In this paper, we report a general, practical and efficient method to monofunctionalize O3-position of CDs by taking advantage of the easily accessible per-3-O-silylated CD 34,35 derivatives as well as the acid-sensitivity of O-silyl ether group.…”