Easier to Twist than Bend: The Scope of the Bridge Formation Approach to Naphthalenophane Synthesis

Abstract

Twisting anthracene and higher acenes can alter their optical, magnetic, and electronic properties. To test the effect of twisting on the lower homologue, naphthalene, we synthesized tethered naphthalenophanes bearing alkyl bridges. Both X-ray structure and DFT calculations show that hexyl and butyl bridges induce a 6° and 12° end-to-end twist on the naphthalene unit, respectively. Attempts to increase the twisting further using shorter tethers resulted in an elimination product. Enantiomerically pure naphthalenophanes display strong chiroptical properties, which intensify with increasing twist. Attempts to induce bending, rather than twisting, using the same synthetic methodology, resulted in intermolecular dimerization, yielding macrocyclic naphthalenes. This work highlights the importance of steric hindrance in the synthesis of curved cyclophanes using the bridge formation approach.