SYNTHESIS AND CHIRAL RECOGNITION OF OPTICALLY-ACTIVE CROWN ETHERS INCORPORATING A HELICENE MOIETY AS THE CHIRAL CENTER

The synthesis of optically active crown ethers (8), (14), and (18) incorporating helicene molecular frameworks is reported. Their chiral recognition properties have been examined and show that (M)-(-)-(14), although of the same helicity as (M)-(-)-(8) and (M)-(-)-(18), exhibits opposite chiral recognition for the transport of methyl phenylglycinate, 1-phenylethylamine, and 1,2-diphenylethylamine, and that the pentahelicene crown (8) has a higher enantiomer selectivity than the hexahelicene crown (14) and hexa[7]circulene crown (18) towards these substrates. At 6.0-6.2% transport using (8), the optical purity of methyl phenylglycinate and 1,2-diphenylethylamine was as high as 77-82%.