Synthesis and chiral recognition of optically active crown ethers incorporating a helicene moiety as the chiral centre

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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%.