Inherently Chiral Iminoresorcinarenes through Regioselective Unidirectional Tautomerization

Tetraformylresorcin­[4]­arene
is obtained in 48% yield via a chromatography-free
Duff reaction. The formylated resorcinarene reacts easily with primary
aliphatic and aromatic amines. The resulting imines exist exclusively
in keto-enamine forms. Owing to a system of intramolecular hydrogen
bonds, the reaction selectively leads to regioisomers with C4 symmetry. They possess an inherent chirality
due to a propeller-like skeleton. For chiral amines, inherently chiral
diastereoisomers are observed.