Chiral Macrocycles for Enantioselective Recognition

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