Synthesis of Cage-Shaped Aluminum Aryloxides: Efficient Lewis Acid Catalyst for Stereoselective Glycosylation Driven by Flexible Shift of Four- to Five-Coordination. 
Monomeric cage-shaped aluminum aryl oxides 1Al were synthesized using tripodal triphenolic ligands.  The Lewis acidity and catalytic activity of the obtained 1Al·py were investigated.  The Lewis acidity of 1Al·py originates from the flexible change in the coordination number of the aluminum center, allowing the catalytic O-glycosylation to occur with a high efficiency and an unusual stereoselectivity.