Near-Infrared Fluorescence from In-Plane-Aromatic Cycloparaphenylene Dications

Cycloparaphenylenes (CPPs) are hoop-shaped conjugated hydrocarbons corresponding to partial structures of fullerenes or armchair carbon nanotubes. Here, we examined the fluorescence properties of a series of [<i>n</i>]­cycloparaphenylene dications ([<i>n</i>]­CPP²⁺, <i>n</i> = 5–9), which have unique in-plane aromaticity. The fluorescence peak positions of the [<i>n</i>]­CPP²⁺s shifted to the longer-wavelength region with increasing ring size, reaching the near-infrared region for those with <i>n</i> > 5. The fluorescence quantum yield of [6]­CPP²⁺ was the highest among the [<i>n</i>]­CPP²⁺s examined in this study, and the value was on the same order as that of carbon nanotubes. The Stokes shifts of [<i>n</i>]­CPP²⁺s were smaller than those of neutral [<i>n</i>]­CPPs, which do not have in-plane aromaticity. Theoretical calculations indicate that [<i>n</i>]­CPP²⁺s undergo smaller structural changes upon S₀–S₁ transition than [<i>n</i>]­CPPs do, and this is responsible for the difference of the Stokes shift. Furthermore, molecular orbital analysis reveals that the S₀–S₁ transition of smaller [<i>n</i>]­CPP²⁺s has an electric-dipole-forbidden character due to HOMO → LUMO/HOMO → LUMO+1 mixing. The relatively high fluorescence quantum yield of [6]­CPP²⁺ is considered to arise from the balance between relatively allowed character and the dominant effect of energy gap

Hitoyol A and B, Two Norsesquiterpenoids from the Basidiomycete <i>Coprinopsis cinerea</i>

Hitoyol A (<b>1</b>), an unprecedented norsesquiterpenoid with an <i>exo</i>-tricyclo­[5.2.1.0^2,6]­decane skeleton, was isolated from the culture broth of Basidiomycete <i>Coprinopsis cinerea</i> along with a novel skeletal hitoyol B (<b>2</b>) containing 4-cyclopentene-1,3-dione. Their structures and absolute configurations were analyzed by single-crystal X-ray diffraction and electronic circular dichroism spectroscopic methods. Compound <b>1</b> is possibly biosynthesized through decarboxylation-induced cyclization of lagopodin B, a known cuparene-type sesquiterpenoid. Compound <b>2</b> showed weak antimalarial activity with an IC₅₀ of 59 μM

Mechanistic Study on Aryl-Exchange Reaction of Diaryl‑λ³‑iodane with Aryl Iodide

Because of its hyper-leaving ability, as well as its strong oxidizing ability, diaryl­(triflato)-λ³-iodane transfers one of the aryl groups to iodoarenes simply upon gentle heating (>85 °C) in nonpolar solvents. We have performed an in-depth mechanistic study of this unusual aryl transfer reaction. A combination of experimental (product analysis, kinetic study, and substituent effects) and density functional theoretical approaches revealed that the reaction proceeds through a concerted bimolecular transition state, in which <i>ipso</i>-carbon binds loosely to both iodine centers. We also evaluated electronic effects on the thermodynamic stability of diaryl-λ³-iodanes

Hitoyol A and B, Two Norsesquiterpenoids from the Basidiomycete <i>Coprinopsis cinerea</i>

Hitoyol A (<b>1</b>), an unprecedented norsesquiterpenoid with an <i>exo</i>-tricyclo­[5.2.1.0^2,6]­decane skeleton, was isolated from the culture broth of Basidiomycete <i>Coprinopsis cinerea</i> along with a novel skeletal hitoyol B (<b>2</b>) containing 4-cyclopentene-1,3-dione. Their structures and absolute configurations were analyzed by single-crystal X-ray diffraction and electronic circular dichroism spectroscopic methods. Compound <b>1</b> is possibly biosynthesized through decarboxylation-induced cyclization of lagopodin B, a known cuparene-type sesquiterpenoid. Compound <b>2</b> showed weak antimalarial activity with an IC₅₀ of 59 μM