Dedicated to the memory of Professor Masahiko Iyoda, who passed away on September
21, 2023.
Abstract
Highly symmetrical and aesthetically pleasing molecules have attracted the attention
of organic chemists. We synthesized new highly symmetric stereogenic π-conjugated
macrocycles with planar or axial chirality. Macrocyclic oligomers synthesized by Yamamoto
coupling or Suzuki–Miyaura cross-coupling from the π-unit containing chirality. These
cyclization reactions gave multiple oligomers in relatively high yields. We then elucidated
their structures and investigated their chiroptical properties, including circular
dichroism (CD) and circularly polarized luminescence (CPL). Because of the selection
rule for rigid and symmetric structures, these macrocycles exhibit a high dissymmetry
factor (g
abs or g
lum) for circularly polarized light in CD or CPL. Several rigid cyclic compounds retain
a highly symmetric structure in the excited state and exhibit higher g
lum values than common chiral organic compounds. This Account provides a brief background
regarding chiroptical properties, followed by a summary of the various macrocycles
synthesized in this study. We are glad if this Account will be a source of ideas not
only for chemists working with π-conjugated compounds, but also for synthetic chemists
working with chiral compounds, especially those engaged in asymmetric synthesis.
1 Introduction
2 Brief Description of Chiroptical Properties
3 Stereogenic Macrocycle Based on [2.2]Paracyclophane
3.1 Stereogenic Double-decker Oligothiophene
3.2 Stereogenic Biselenophene Macrocycle
3.3 Helical Oligophenylene Linked with [2.2]Paracyclophane
4 Stereogenic Macrocycle Based on Binaphthyl
4.1 Cyclic Oligomer of Chiral Binaphthyl
4.2 Doubly Twisted Binaphthyl Dimer
4.3 Cyclic Oligomer of Binaphthyl Extended with Paraphenylene
4.4 Curved Helical Paraphenylene Anchoring Chiral Binaphthyl
4.5 Binaphthyl-Hinged [5]-Helicene
5 Summary
Key words
macrocycle - chirality - circularly polarized luminescence - [2.2]paracyclophane -
binaphthyl - oligothiophene - paraphenylene - helicene