Structural elucidation of two [1.4]metacyclophanes isomers by 2D NMR analysis

Abstract

The acid-catalysed condensation of diethyl benzene-1,3diyldioxy diacetate and p-methyl-benzaldehyde provides an hydroxy-derivatised resorcinarene or [1.4]metacyclophane as a mixture of two isomeric compounds ( IIa and IIb), which were separated by recrystallisation and column chromatography. Under homogeneous as well as under heterogeneous acidic conditions, we obtained the same isomer ( IIa) as the main product of the reaction. The 1H NMR assignments were made with the help of 2D COSY-45 and HC COSY. The 13C-multiplicities were established by carrying out DEPT experiments whereas the stereochemistry has been determined by a series of NOESY and NOE difference experiments. The results revealed that IIa isomer has a cis– trans– trans configuration (in a chair like conformation) and IIb isomer has a cis– cis– cis configuration (in a boat like conformation). The spectral properties (MS, IR and UV) are also presented.