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 C 4 ‐symmetric rccc ‐resorc[4]arenes. Separation of these isomers was achieved by mono‐ O ‐functionalization of the rccc ‐2,8,14,20‐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‐[(2 S )‐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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)