Cyclization of resorcinol monoalkyl ethers with aliphatic aldehydes leads to the corresponding racemic mixtures of C4symmetric rccc-resorcarenes. Separation of these isomers was achieved by mono-O-functionalization of the rccc2,8,14,20-tetramethylresorcarene (2) with (S)-(+)-10-camphorsulfonyl chloride leading to a diastereomeric mixture of (+)-5a and (-)-5b. After removal of the chiral auxiliary the inherently chiral pure enantiomers (+)-2 and (-)-2 were obtained. Further enantiomerically pure rccc-resorcarenes were obtained by cyclization of (+)-3-[(2S)-2-methylbutoxy]phenol (6) followed by chromatographic separation. The resulting diastereomeric resorcarenes (+)-7a and (-)-7b were examined by CD spectroscopy, showing a perfect mirror image in all solvents examined. This indicates that the resorcarene cavities of (+)-7a and (-)-7b are essentially enantiomers of each other.
- Asymmetric synthesis
- Circular dichroism