Cavity-extended inherently chiral resorein[4]arenes: Synthesis and chiroptical properties of the cycloenantiomers

Inherently chiral resorcin[4]arenes 2 and 3 were prepared from enantiomerically pure C-4-symmetric rccc-2,8,14,20-tetraisobutyl-4,10,16,22-tetra-O-methylresorcin[4]arene (1). The four 2-bromobenzyl ether residues in precursor 2 were introduced as halide moieties to partake in an intramolecular Pd-catalysed C-C cross-coupling reaction to give tetrabiaryl ether compound 3. The absolute configurations could be derived from the starting compounds and were assigned as (M,R)-(-)-2 and (PS)-(+)-2 for the tetrakis(2'-bromobenzyl) ether compounds as well as (M,R)-(-)-3 and (PS)-(+)-3 for the cavity-extended resorcinarenes. The carbon scaffold of 3 contains four new stereogenic axes whose configurations were assigned by single-crystal X-ray analysis. The simulation of the CD spectra by time-dependent Pariser-Parr-Pople calculations (TDPPP) based on the X-ray data gave very good images of the experimental spectra. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).