Wataru Ichinose

Optical Resolution of Aromatic Alcohols Using Silica Nanoparticles Grafted with Helicene

Optically active silica nanoparticles, with a 70-nm diameter, grafted with (P)-1,12-dimethyl-8-methoxycarbonylbenzo[c]phenanthrene-5-carboxyamide were synthesized, and their use in the kinetic resolution of aromatic alcohols was examined. Up to 61% ee for (S)-2,2-dimethyl-1-phenyl-1-propanol was obtained by a preferential precipitation of aggregates formed with (P)-nanoparticles.

Multiple States of Dimeric Aggregates Formed by (Amido–ethynyl)helicene Bidomain Compound and (Amido–ethynyl–amido)helicene Tridomain Compound

An (amido-ethynyl)helicene bidomain compound and an (amido-ethynyl-amido)helicene tridomain compound were synthesized. The multidomain compounds were designed on the basis of previous findings that amido and ethynyl oligomers form dimeric aggregates with properties orthogonal to each other. Four aggregate states of multidomain compounds, namely, all-dimer, amido-dimer, ethynyl-dimer, and random-coil states, were obtained in different solvents, which were analyzed by circular dichroism (CD), UV/Vis, (1)H NMR, and IR spectroscopy; vapor pressure osmometry (VPO); dynamic light scattering (DLS); and atomic force microscopy (AFM). The amido and ethynyl domains independently aggregated and disaggregated in a two-state manner. Reversible structural changes occurred for a tridomain compound between the ethynyl-dimer/random-coil state and the all-dimer/amido-dimer state with heating and cooling. Two structural change processes with different properties were obtained using a single compound.

Equilibrium Shift in Solution: Molecular Shape Recognition and Precipitation of a Synthetic Double Helix Using Helicene‐Grafted Silica Nanoparticles

Chiral silica nanoparticles (70 nm) grafted with (P)-helicene recognized the molecular shape of double helix and random coil (P)-ethynylhelicene oligomers in solution. A mixture of the (P)-nanoparticles and double helix precipitated much faster than a mixture of the (P)-nanoparticles and random coil, and the precipitate contained only the double helix. The mixture of the (P)-nanoparticles and (P)-ethynylhelicene pentamer reversibly dispersed in trifluoromethylbenzene upon heating at 70 °C and precipitated upon cooling at 25 °C. When a 10:90 equilibrium mixture of the double helix and random coil in solution was treated with the (P)-nanoparticles, the double helix was precipitated in 53% yield and was accompanied by equilibrium shift.

Heteroaggregation between isomeric amido-ethynyl-amidohelicene tridomain oligomers.

Three isomers, i.e., P4M5P4-1, M4P5M4-1, and M4M5M4-1, of amido-ethynyl-amidohelicene tridomain oligomers were synthesized. P4M5P4-1 formed four homoaggregate states, i.e., all-dimer, amido-dimer, ethynyl-dimer, and random-coil states, by independent aggregation and disaggregation at the ethynyl and amido domains. Then, possible combinations of heteroaggregation were examined between the isomeric tridomain oligomers P4P5P4-1, P4M5P4-1, M4P5M4-1, and M4M5M4-1. When P4P5P4-1 and P4M5P4-1 were mixed in THF, to which trifluoromethylbenzene was added, heteroaggregates with an all-dimer structure were formed without forming homoaggregates. The heteroaggregation initially occurred at the central ethynyl domain, which was followed by the aggregation at the amido domains. Heteroaggregates were also formed using the combinations P4P5P4-1/M4M5M4-1 and P4M5P4-1/M4P5M4-1, and the results indicated an important role for the central ethynyl domain for heteroaggregation.