A tellura-Baeyer-Villiger oxidation: one-step transformation of tellurophene into chiral tellurinate lactone

Spiro-Buckybowls: Synthesis and Selective Transformations Toward Chiral and Nonlinear Optical Polycycles

Integration of spirocycles with buckybowls is a promising strategy to construct three-dimensional (3D) curved π-systems and to endow distinctive physicochemical features arising from buckybowls. Herein, a series of carbon-bridged spiro-type heterosumanenes (spiro-HSEs) were synthesized by combining 9,9'-spirobifluorene and dichalcogenasumanenes (DCSs). It is found that spiro-conjugation plays an important role in the geometric and electronic structures of spiro-HSEs. The bowl depth of DCSs moiety becomes larger in the spiro-HSEs. Owing to the Jahn-Teller (J-T) effect, two DCSs segments of spiro-HSEs have different bowl depths accompanied with the unequal distribution of charge in radical cation state. Taking advantage of the typical reactions of DCSs, selective transformations of spiro-HSEs have been adopted in accordance to the nature of chalcogen atoms (S, Se, Te) to bestow the value-added functionalities. The emissive property is enhanced by converting the thiophene rings of S-doped spiro-HSE into thiophene S,S-dioxides. A chiroptical polycycle could be produced by ring-opening of the edge benzene of Se-doped spiro-HSE. The covalent adduct of Te-doped spiro-HSE with Br2 forms non-centrosymmetric halogen-bonded networks, resulting in the high performance second-order nonlinear optics (NLO).

Radical Cation Salts of Hetera-Buckybowls: Polar Crystals, Negative Thermal Expansion and Phase Transition

Radical cation salts of π-conjugated polycycles are rich in physical properties. Herein, two kinds of hetera-buckybowls, ethoxy-substituted trithiasumanene (3SEt) and triselenasumanene (3SeEt), are synthesized as electron donors. Galvanostatic oxidation of them affords radical cation salts (3SEt)5 (TTFMPB)3 , (3SeEt)5 (TTFMPB)3 , (3SEt)4 PMA, and (3SeEt)4 PMA, where PMA is Keggin-type phosphomolybdate and TTFMPB is tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate. In these salts, 3SEt/3SeEt are partially charged and show distinct conformation change with the site charge and counter anions. In TTFMPB salts, (TTFMPB)- forms hexagonal channels that accommodate the packing columns of 3SEt/3SeEt. In particular, (3SEt)5 (TTFMPB)3 adopts the R3c space group and is a polar crystal with the columns of 3SEt all in the up-bowl direction. The PMA salts of 3SEt/3SeEt are polar crystals (C2 space group) with 3SEt/3SeEt being planar and forming columnar stacks. (3SeEt)4 PMA shows a structural modulation below 200 K, namely, negative thermal expansion (NTE) of the unit cell volume and enlargement of the intermolecular distances between neighboring 3SeEt molecules. The four salts are semiconductors with an activation energy of 0.18-0.38 eV. The conductivity of (3SeEt)4 PMA shows a reversible transition upon cooling and heating, in accordance to the NTE structural modulation. This work paves the way toward conducting materials based on hetera-buckybowls.

Transforming Hetera-Buckybowls into Chiral Conjugated Polycycles Incorporating Epoxycyclooctadiene: a Two-Step Approach

Chiral π-conjugated polycycles have garnered increasing attention due to versatile applications in optoelectronic materials and biological sciences. In this study, we report the synthesis of chiral π-conjugated polycycles incorporating a chiral epoxycyclooctadiene moiety. Our synthetic strategy capitalizes on the novel reactions of hetera-buckybowl triselenasumanene (TSS) and is achieved in two-step manner. Firstly, the TSS is regio-selectively transformed into its ortho-quinone form. Subsequently, the nucleophilic addition reactions of TSS ortho-quinone by phenylethynides are metal ion-dependent. When utilizing (phenylethynyl)magnesium bromide as the nucleophile, two phenylethynyls are furnished onto the edged benzene ring of TSS. When the nucleophile is (phenylethynyl)lithium, a cascade of nucleophilic addition, intermolecular electron-transfer, ring-opening, and tetradehydro-Diels-Alder (TDDA) reactions occur sequentially in one-pot, ultimately affording chiral π-conjugated polycycles featuring the epoxycyclooctadiene moiety as an integral part of their backbones. This work represents a step forward in the synthesis of chiral π-conjugated polycycles using TSS as synthon.

Synthesis of the C70 Fragment Buckybowl, Homosumanene, and Heterahomosumanenes via Ring-Expansion Reactions from Sumanenone

Bowl-shaped aromatic molecules, buckybowls, are attractive molecules because of the unique properties derived from their curved-π scaffolds. Doping heteroatoms into buckybowl frameworks is a powerful method to change their structural and electronical properties. Herein, we report the synthesis of C₇₀ fragment buckybowl, homosumanene, and heterahomosumanenes having a lactone moiety and a lactam moiety via three ring-expansion reactions using sumanenone as a common intermediate. X-ray diffraction analysis of the single crystals reveals their columnar packing structure with a shallow bowl-depth. The lactam moiety is readily derivatized to give azahomosumanene derivatives, nitrogen-doped analogues of homosumanene possessing a pyridine ring at the peripheral carbon. The synthetic application of the α-phenyl azahomosumanene as a cyclometalating ligand with platinum also revealed its utility for preparing a metal complex bearing a buckybowl ligand.

Transforming electron-rich hetero-buckybowls into electron-deficient polycycles

Oxidation of trichalcogenasumanenes (TCSs) with NO species results in the simultaneous formation of ortho-quinone and diester groups. This reaction enables the transformation of electron-rich TCSs into electron-deficient polycycles.