Syntheses and Reactions of Crown Ether-Bridged Stilbenes.

A high-yield synthesis of o, o′ crown ether-bridged stilbenes 3b–e by reductive McMurry condensation of (2-formylphenyl)oligoethylene glycols 2b–e with facile (E/Z) diastereomer separation by selective cation complexation is described. Derivatization of the stilbene double bonds of (E)- or (Z)-3b–e affords dihydroxy crown ethers 4c, d and 5c, d diastereo- and enantioselectively. Likewise, trans- and cis-epoxides 11b–d and 12b–d are stereospecifically obtained. A crown ether-bridged diphenylacetaldehyde 13 is formed by rearrangement of 11c or 12c. Photocyclization of 3e yields large-ring 1,8-phenanthrene crown ether 18. The crystal structures of racemic 5c and of 12d are presented. A high caesium selectivity compared to the other alkali metal and alkaline earth cations is found for ion exchange membranes with incorporated crown ether (Z)-3c.