Synthesis of enantiopure planar chiral bis‐( para )‐pseudo‐ meta ‐type [2.2]paracyclophanes

A new type of planar chiral ( R p )‐ and ( S p )‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes was prepared from racemic 4,7,12,15‐tetrabromo[2.2]paracyclophane as the starting substrate. Regioselective lithiation and transformations afforded racemic bis‐( para )‐pseudo‐ meta ‐type [2.2]paracyclophane (4,15‐dibromo‐7,12‐dihydroxy[2.2]paracyclophane). Its optical resolution was performed by the diastereomer method using a chiral camphanoyl group as the chiral auxiliary. The diastereoisomers were readily isolated by simple silica gel column chromatography, and the successive hydrolysis afforded ( R p )‐ and ( S p )‐bis‐( para )‐pseudo‐ meta ‐type [2.2]paracyclophanes (( R p )‐ and ( S p )‐4,15‐dibromo‐7,12‐dihydroxy[2.2]paracyclophanes). They can be used as pseudo‐ meta ‐substituted chiral building blocks.