Lecourt Thomas, Herault Alexandre, Pearce Alan J, Sollogoub Matthieu, Sinaÿ Pierre
Département de Chimie, UMR 8642 CNRS, 24 rue Lhomond 75231, Paris Cedex 05, France.
Chemistry. 2004 Jun 21;10(12):2960-71. doi: 10.1002/chem.200305683.
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.
为了解释二异丁基氢化铝（DIBAL-H）和三异丁基铝（TIBAL）对多苄基化糖或环糊精具有显著的区域选择性脱O-苄基化性质，我们提出了一个合理的机理依据，该依据关键涉及生成产物的2:1铝-苄基化糖络合物的动力学形成。为使反应发生，一对相邻的氧原子首先应能够与第一当量的铝试剂形成螯合络合物，该络合物要么是与四配位铝物种形成的高度易变络合物，要么是五配位络合物。然后，第二当量试剂通过优先与所选氧原子对中的一个氧原子配位来诱导脱O-烷基化的区域选择性。
