Enantiopure (P)- and (M)-3,14-bis(o-hydroxyaryl)tetrahydrobenzo[5] helicenediols and their helicene analogues: Synthesis, amplified circularly polarized luminescence and catalytic activity in asymmetric hetero-Diels-Alder reactions

Three pairs of enantiopure (P)- and (M)-3,14-bis(o-hydroxyaryl)tetrahydrobenzo[5]helicenediols (ArOH-H[5]HOLs), and enantiomers (P)- and (M)-3,14-bis(o-hydroxyphenyl)benzo[5]helicene-diols (PhOH-[5]HOLs) were designed and synthesized. It was found that compared with ArOH-H[5]HOLs, PhOH-[5]HOLs not only showed obvious red-shifts in both absorption and emission spectra, but also exhibited more intense CPL with amplified g(lum), which might be attributed to the more rigid structure of PhOH-[5]HOLs. However, rigid PhOH-[5]HOLs was less effective in the catalytic asymmetric hetero-Diels-Alder (HAD) reactions than those of ArOH-H[5]HOLs with the flexible tetrahydro[5]helicene backbone that could adjust conformation to suit the substrates. Therefore, the helical chirality amplification and chirality transfer could be efficiently achieved by adjusting the rigid and flexible structures of helical molecules, which might provide a useful strategy to optimize the structure of helicence derivatives for their applications in chiroptical materials and asymmetric catalysis. (C) 2018 Elsevier Ltd. All rights reserved.