Synthesis, Structures and Lewis-Acid-Induced Isomerization of 8-Methoxy[2.2]metaparacyclophanes and a DFT Study

Abstract

Methyl substituted 8-methoxy[2.2]MPCPs 8 a–b were obtained via thiacyclophane and its oxidized products. Lewis acid-catalyzed (AlCl 3 -MeNO 2 ) reactions of 5-tert-butyl-8-methoxy-12,13,15,16-tetramethyl[2.2]MPCP 8 b under various conditions led to transannular cyclization and isomerization reactions, affording the considerably less-strained 5-tert-butyl-8-methoxy[2.2]MPCP 9, 5-tert-butyl-8-hydroxy-14,16,17,18-tetramethyl[2.2]metacyclophane 10 and pyrene derivatives 11 and 12. However,on prolonging the reaction time to 3 h for 8 b, the major product is 5-tert-butyl-8-hydroxy[2.2]MPCP 10. These reactions are strongly affected by the size and properties of the C-8 substitutents as well as the methyl substitutents on the para-linked benzene rings, which increase the strain in the molecules. The 1 H NMR spectra and X-ray crystallographic analysis of 8 b revealed that it adopts a syn-conformation both in solution and in the solid state.