Naphthalenophane formaldehyde acetals as candidate structures for the generation of dynamic libraries via transacetalation processes

Lower cyclic oligomers C2-C5 of a family of naphthalenophane formaldehyde acetals Cn have been isolated and characterized, the dimer being obtained in two atropisomeric forms, syn-C2 and anti-C2, as confirmed by X-ray analysis. The investigated cyclophanes showed interesting recognition properties towards electron-poor guests (K>10^5 M-1 for association of the guanidinium ion with C3 in chloroform). A library of macrocycles was generated by acid catalyzed transacetalation of Cn in chloroform, but the dynamic nature of the system was spoiled by the occurrence of irreversible reaction pathways promoted by the relatively easy formation of extended benzyl-like carbocations I.