Efficient and chromatography-free methodology for the modular synthesis of oligo-(1 H -pyrazol-4-yl)-arenes with controllable size, shape and steric bulk

Dissecting Porosity in Molecular Crystals: Influence of Geometry, Hydrogen Bonding, and [π···π] Stacking on the Solid-State Packing of Fluorinated Aromatics

Porous molecular crystals are an emerging class of porous materials that is unique in being built from discrete molecules rather than being polymeric in nature. In this study, we examined the effects of molecular structure of the precursors on the formation of porous solid-state structures with a series of 16 rigid aromatics. The majority of these precursors possess pyrazole groups capable of hydrogen bonding, as well as electron-rich aromatics and electron-poor tetrafluorobenzene rings. These precursors were prepared using a combination of Pd- and Cu-catalyzed cross-couplings, careful manipulations of protecting groups on the nitrogen atoms, and solvothermal syntheses. Our study varied the geometry and dimensions of precursors, as well as the presence of groups capable of hydrogen bonding and [π···π] stacking. Thirteen derivatives were crystallographically characterized, and four of them were found to be porous with surface areas between 283 and 1821 m² g^-1. Common to these four porous structures were (a) rigid trigonal geometry, (b) [π···π] stacking of electron-poor tetrafluorobenzenes with electron-rich pyrazoles or tetrazoles, and

Synthesis of 4-substituted pyrazole-3,5-diamines via Suzuki-Miyaura coupling and iron-catalyzed reduction

A general and efficient synthesis of 4-substituted-1H-pyrazole-3,5-diamines was developed to access derivatives with an aryl, heteroaryl, or styryl group, which are otherwise relatively difficult to prepare. The first step is based on the Suzuki-Miyaura cross-coupling reaction utilizing the XPhos Pd G2 precatalyst. The coupling reactions of 4-bromo-3,5-dinitro-1H-pyrazole with the electron-rich/deficient or sterically demanding boronic acids enabled the production of the corresponding dinitropyrazoles. The subsequent iron-catalyzed reduction of both nitro groups with hydrazine hydrate accomplished the synthesis. The additional demethylation of the 4-methoxystyryl derivative allowed the production of the carboanalog of CAN508 reported as a selective CDK9 inhibitor.

Solventless Synthesis of Poly(pyrazolyl)phenyl-methane Ligands and Thermal Transformation of Tris(3,5-dimethylpyrazol-1-yl)phenylmethane

The solventless synthesis of tris(pyrazolyl)phenylmethane ligands of formula C₆H₅C(Pz^R2)₃ (R = H, Me), starting from PhCCl₃ and 3,5-dimethylpyrazole (Pz^Me2) or pyrazole (Pz) was performed. The sterically crowded C₆H₅C(Pz^Me2)₃ is thermally transformed into the bis(pyrazolyl)(p-pyrazolyl)phenylmethane ligand Pz^Me2-C₆H₄CH(Pz^Me2)₂. In this compound both Pz^Me2 rings are linked through the N-atom to the methine C-atom. At higher temperatures, the binding mode of Pz^Me2 changes from N1 to C4. All transformations occurred via quinonoid carbocation intermediates that undergo an aromatic electrophilic substitution on the 4-position of Pz^Me2. Reaction conditions were established to obtain five tris(pyrazolyl)phenylmethane ligands in moderate to good yields. ¹H- and ¹³C-NMR spectroscopy and X-ray diffraction of single crystals support the proposed structures.