Triisobutylaluminium and diisobutylaluminium hydride as molecular scalpels: the regioselective stripping of perbenzylated sugars and cyclodextrins.
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.
Lecourt
Thomas
T
Département de Chimie, UMR 8642 CNRS, 24 rue Lhomond 75231, Paris Cedex 05, France.
Herault
Alexandre
A
Pearce
Alan J
AJ
Sollogoub
Matthieu
M
Sinaÿ
Pierre
P
D000535:Aluminum / Q000737:chemistry*; D001593:Benzyl Compounds / Q000737:chemistry*; D002236:Carbohydrate Conformation; D003505:Cyclodextrins / Q000737:chemistry*; D004987:Ethers / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D016339:Spectrometry, Mass, Fast Atom Bombardment
D001593:Benzyl Compounds; D003505:Cyclodextrins; D004987:Ethers; D009942:Organometallic Compounds; D000535:Aluminum; C035719:diisobutylaluminum