The trans,anti,trans- and trans,syn,trans-isomers of dicyclohexyl-18-crown-6 and their complexes

Abstract

The stereospecific synthesis of the trans,anti,trans-(2a) and trans,syn,trans-(2b) isomers of dicyclohexyl-18-crown-6 (2) from the diastereoisomeric (±)-(6a) and meso-(6b) 2,2′-methylenedioxydicyclohexanols has been achieved. A one-step synthesis of the di-trans-isomers (2a and b) from (±)-cyclohexane-trans-1,2-diol (3) is accompanied by the formation of some trans-cyclohexyl-9-crown-3 (10). trans,syn,trans-Dicyclohexyl-18-crown-6 (2b) forms crystalline complexes with alkali metal, ammonium, and primary alkylammonium salts. In methanolic solutions, the stability constants for the complexes with sodium, potassium, and caesium chlorides are greater for the cis,anti,-cis-(2c) and cis,syn,cis-(2d) isomers than they are for either of the di-trans-isomers (2a and b). Also, within each pair of isomers, the syn-isomers (2b and d) form stronger complexes than the anti-isomers (2a and c). All four isomers exhibit selectivity for binding potassium ions.