First synthesis, isolation and characterization of enantiomerically pure and inherently chiral resorc[4]arenes by lewis acid cyclization of a resorcinol monoalkyl ether

Cyclization of resorcinol monoalkyl ethers with aliphatic aldehydes leads to the corresponding racemic mixtures of C₄symmetric rccc-resorc[4]arenes. Separation of these isomers was achieved by mono-O-functionalization of the rccc2,8,14,20-tetramethylresorc[4]arene (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-resorc[4]arenes were obtained by cyclization of (+)-3-[(2S)-2-methylbutoxy]phenol (6) followed by chromatographic separation. The resulting diastereomeric resorc[4]arenes (+)-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.