Unprecedented Encapsulation of Carbonyl Guest with Designer Lewis Acid Receptor.

A reaction chamber is formed by a cage compound in which a dicarbonyl guest molecule is encapsulated by two bowl-shaped aluminum tris(2,6-diphenylphenoxide) molecules through Lewis acid-base interactions (structure of complex with 1,4-dimethylpiperazine-2,5-dione depicted). The carbonyl compound held inside the molecular capsule is effectively protected against the approach of external nucleophiles. On the other hand, the chamber is large enough to allow Diels-Alder cycloadditions to take place under mild conditions and with high selectivity.