1,3-Difunctionalization of [1.1.1]propellane through iron-hydride catalyzed hydropyridylation.

Current methodologies for the functionalization of [1.1.1]propellane primarily focus on achieving 1, 3-difunctionalized bicyclo[1.1.1]pentane or ring-opened cyclobutane moiety. Herein, we report an innovative approach for the 1, 3-difunctionalization of [1.1.1]propellane, enabling access to a diverse range of highly functionalized cyclobutanes via nucleophilic attack followed by ring opening and iron-hydride hydrogen atom transfer. To enable this method, we developed an efficient iron-catalyzed hydropyridylation of various alkenes for C - H alkylation of pyridines at the C4 position, eliminating the need for stoichiometric quantities of oxidants or reductants. Mechanistic investigations reveal that the resulting N-centered radical serves as an effective oxidizing agent, facilitating single-electron transfer oxidation of the reduced iron catalyst. This process efficiently sustains the catalytic cycle, offering significant advantages for substrates with oxidatively sensitive functionalities that are generally incompatible with alternative approaches. The strategy presented herein is not only mechanistically compelling but also demonstrates broad versatility, highlighting its potential for late-stage functionalization.

Benzylic Trifluoromethyl Accelerates 1,6-Elimination Toward Rapid Probe Activation.

Activity-based detection of hydrogen sulfide in live cells can expand our understanding of its reactivity and complex physiological effects. We have discovered a highly efficient method for fluorescent probe activation, which is driven by H2S-triggered 1,6-elimination of an α-CF3-benzyl to release resorufin. In detecting intracellular H2S, 4-azido-(α-CF3)-benzyl resorufin offers significantly faster signal generation and improved sensitivity compared to 4-azidobenzyl resorufin. Computed free energy profiles for the 1,6-elimination process support the hypothesis that a benzylic CF3 group can reduce the activation energy barrier toward probe activation. This novel probe design allows for near-real-time detection of H2S in HeLa cells under stimulation conditions.

Site-Selective Pyridine C-H Alkylation with Alcohols and Thiols via Single-Electron Transfer of Frustrated Lewis Pairs.

A unified strategy for the deoxygenative or desulfurative pyridylation of various alcohols and thiols has been developed through a single-electron transfer (SET) process of frustrated Lewis pairs (FLPs) derived from pyridinium salts and PtBu3 . Mechanistic studies revealed that N-amidopyridinium salts serve as effective Lewis acids for the formation of FLPs with PtBu3 , and the generated phosphine radical cation ionically couples with the in situ generated xanthate, eventually affording the alkyl radical through facile ß-scission under photocatalyst-free conditions. The reaction efficiency was further accelerated by visible-light irradiation. This method is conceptually appealing by using encounter complexes in FLP chemistry to promote SET, which provides a previously unrecognized opportunity for the selective heteroarylation of a diverse range of alcohols and thiols with various functional groups, even in complex settings under mild reaction conditions.

Effects of mesiodens on adjacent permanent teeth: a retrospective study in Korean children based on cone-beam computed tomography.

BACKGROUND: Mesiodens can be associated with several complications. The optimal age for treatment, however, remains controversial. AIM: To investigate the three-dimensional (3D) positions of mesiodens using cone-beam computed tomography (CBCT) and determine the association of eruption-related complications of mesiodens with these 3D positions and delayed development of the central incisors. DESIGN: In total, 293 Korean children (383 supernumerary teeth) aged 4-10 years with no history of orthodontic treatment were included. CBCT and panoramic radiography data for all patients were retrospectively investigated with regard to the 3D positions of mesiodens, apical maturity of the permanent first molars, delayed development of the central incisors relative to the apical maturity of the permanent first molars (Nolla's stage), and eruption-related complications of mesiodens. RESULTS: Eruption-related complications were not correlated with any 3D characteristic other than the 'within the arch' position of mesiodens, while they showed a significant correlation with delayed development of the central incisors (P < 0.05). CONCLUSIONS: Mesiodens caused eruption-related complications in 33.7% patients. Moreover, the risk of these complications was higher when mesiodens caused delayed development of the central incisors. These findings can aid clinicians in planning appropriate and timely treatment for mesiodens, with focus on minimising patient discomfort.

Effects of Additional Acid Etching on the Dentin Bond Strengths of One-Step Self-Etch Adhesives Applied to Primary Teeth.

OBJECTIVES: The aim of this study was to evaluate the bond strengths of one-step self-etch adhesives applied to primary tooth dentin with and without additional acid etching. MATERIALS AND METHODS: In total, 154 specimens were prepared using 50 naturally exfoliated primary molars. Four commercial one-step self-etch adhesives were used in this study: Scotchbond™ Universal, All-Bond Universal™, Adper™ Prompt™ L-Pop™, and Clearfil S3 Bond™. Two etch-and-rinse adhesives, Prime & Bond® NT™ and Scotchbond™ Multi-Purpose, served as controls. Microtensile bond strength tests were performed for specimens treated with the one-step self-etch adhesives with and without additional acid etching and those treated with the two etch-and-rinse adhesives. RESULTS: All one-step self-etch adhesives except Adper Prompt L-Pop exhibited increased microtensile bond strength values (p < 0.05) with additional acid etching. A nonsignificant interaction was observed between the type of self-etch adhesive and additional acid etching (p = 0.056). Bond strength comparisons between the self-etch adhesives used without additional acid etching and the etch-and-rinse adhesives revealed significantly higher values for Prime & Bond NT than for All-Bond Universal® (p < 0.05). However, there were no significant differences between any etch-and-rinse adhesive and self-etch adhesive used with additional acid etching, although Clearfil S3 Bond showed greater strength than Adper Prompt L-Pop. CONCLUSIONS: Our results suggest that additional acid etching increases the bond strength of most one-step self-etch adhesives applied to primary tooth dentin. CLINICAL SIGNIFICANCE: Additional acid etching of enamel and dentin can be recommended to increase the bond strength of one-step self-etch adhesives applied to primary teeth. (J Esthet Restor Dent 29:110-117, 2017).

Hierarchically assembled one-dimensional TiO2 nanostructures: echinoid- and labyrinth-shaped TiO2 crystals for dye sensitized solar cell.

TiO2 nanostructures have been studied intensively for decades for their photocatalytic properties. Recently, several interesting TiO2 nanostructures with controlled surface facets or shapes were reported. However, systemic approaches to obtain designed nanostructures are still rare. Here, various hierarchical 1D TiO2 nanostructures, including TiO2 nanorods, echinoid-shaped TiO2, and labyrinth-structured TiO2, were fabricated by a one-pot hydrothermal process. Concentrated HCl was added to a solution having a Ti4+/H+ ratio that ranged from 1/4 to 1/8. The highly concentrated acid stabilized hydrolysis and hindered condensation, thereby balancing nucleation and growth of TiO2 nanostructures in the hydrothermal treatment step. Dye-sensitized solar cells prepared using the hierarchical 1D TiO2 nanostructures have shown higher photon to current conversion efficiency in the wavelength over 600 nm compared to those prepared with TiO2 nanoparticles.