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 C-4 symmetry. They possess an inherent chirality due to a propeller-like skeleton. For chiral amines, inherently chiral diastereoisomers are observed.