Easy Access to Planar-chiral Induction of Paracyclophanes

Paracyclophanes are macrocyclic compounds which include an aromatic ring directly para-substituted with an alkyl chain. 1,11-Dioxa[11]paracyclophane (1) has the structure with both terminals of a nine-membered alkyl chain moiety bound at the para-position of two atoms of oxygen on a phenyl group. Chiral lithiation of 1 successfully proceeds by treatment with sec-butyllithium and (-)-sparteine in ether at -78 ^oC. Subsequent reactions with electrophiles afford the desired mono-substituted planar-chiral paracyclophanes with excellent enantioselectivities. After mono-lithiation of 1 at -78 ^oC, further lithiation of it can be accomplished by the addition of sec-butyllithium and rising to -20 ^oC. The generated di-lithiated intermediate reacts with electrophiles to give the di-substituted C₂-symmetrical planar-chiral paracyclophanes with nearly pure optical activities. So, it is expected that 1 is applicable to use for the synthesis of optically active compounds and functional material science.