Access to the Syn diastereomers of cryptophane cages using HFIP.

Cryptophane cages can adopt either an anti or syn configuration that present different recognition properties. While the synthesis of anti -cryptophanes is well reported, the synthesis of syn -cryptophanes remains a challenge. Herein, we demonstrate that the use of HFIP as a co-solvent during the second ring closure reaction significantly affects the regioselectivity, providing easier access to the syn -cryptophane stereomers.