Chiral Macrocycles\nfor Enantioselective Recognition

The efficient synthesis of chiral macrocycles with highly\nenantioselective\nrecognition remains a challenge. We have addressed this issue by synthesizing\na pair of chiral macrocycles, namely, <i>R</i>/<i>S</i>-BINOL[2], achieving total isolated yields of up to 62% through a\ntwo-step reaction sequence. These macrocycles are readily purified\nby column chromatography over silica gel without the need for chiral\nseparation, thus streamlining the overall synthesis. <i>R</i>/<i>S</i>-BINOL[2] demonstrated enantioselective recognition\ntoward chiral ammonium salts, with enantioselectivity (<i>K</i><sub><i>S</i></sub>/<i>K</i><sub><i>R</i></sub>) values reaching up to 13.2, although less favorable separations\nwere seen for other substrates. <i>R</i>/<i>S</i>-BINOL[2] also displays blue circularly polarized luminescence with\na |<i>g</i><sub>lum</sub>| value of up to 2.2 × 10<sup>–3</sup>. The <i>R</i>/<i>S</i>-BINOL[2]\nmacrocycles of this study are attractive as chiral hosts in that they\nboth display enantioselective guest recognition and benefit from a\nconcise, high-yielding synthesis. As such, they may have a role to\nplay in chiral separations.