Triisobutylaluminium and Diisobutylaluminium Hydride as Molecular Scalpels: The Regioselective Stripping of Perbenzylated Sugars and Cyclodextrins

Abstract

To explain the remarkable regioselective de-O-benzylating properties of diisobutylaluminium hydride (DIBAL-H) and triisobutylaluminium (TIBAL) towards polybenzylated sugars or cyclodextrins, we propose a plausible mechanistic rationale critically involving the kinetic formation of a product-generating 2:1 Al-benzylated sugar complex. For the reaction to occur, one pair of adjacent oxygen atoms should first be able to form a chelation complex with the first equivalent of aluminium reagent, either a highly fluxional complex with tetracoordinate aluminium species or a pentacoordinate one. The second equivalent then induces the regioselectivity of the de-O-alkylation by coordinating preferentially to one of the oxygen atoms of the selected pair.

Cyclodextrin-based multivalent glycodisplays: covalent and supramolecular conjugates to assess carbohydrate–protein interactions

“…Differences in the steric accessibility and acidity of the three types of hydroxyls in the molecule have been taken into account to conceive efficient position-selective and face-selective chemical functionalization methodologies. [17][18][19][20][21][22][23][24][25][26][27] A variety of multivalent conjugates with diverse architectures becomes then accessible through appropriate ligation chemistries (Fig. 1).…”

Site-selective hexa-hetero-functionalization of α-cyclodextrin an archetypical C6-symmetric concave cycle

“…This reaction is a ARTICLE debenzylation reaction discovered serendipitously 45,46 and operated by diisobutylaluminium hydride (DIBAL-H) leading to CD A,D-diol 3 from perbenzylated CD 1 (ref. 47). The mechanism of the reaction involves the chelation of the aluminium reagent between the primary and the endocyclic oxygen atoms of a glucopyranosidic unit as shown in CD 4 (Fig.…”

Regioselective Double Capping of Cyclodextrin Scaffolds

“…[1,8] The more challenging task of obtaining tetrafunctionalised species in a regioselective manner has been recently addressed by several groups. For example, one-step diisobutylaluminum hydride (DIBAL-H) induced deprotections of perbenzylated [9] CDs have been employed to produce tetrafunctionalised a-, b-and g-CDs in low to moderate yields, but with high regioselectivity. [10] Tetrafunctionalised a-and b-CDs are also accessible through multistep syntheses involving two non-consecutive debenzylation steps.…”