Because of the peculiar dynamic covalent reactivity of boronic acids to form tetraboronate derivatives, interest in using their aryl derivatives in materials science and supramolecular chemistry has risen. Nevertheless, their ability to form H-bonded complexes has been only marginally touched. Herein we report the first solution and solid-state binding studies of the first double-H-bonded DD·AA-type complexes of a series of aromatic boronic acids that adopt a syn-syn conformation with suitable complementary H-bonding acceptor partners. The first determination of the association constant (K) of ortho-substituted boronic acids in solution showed that K for 1:1 association is in the range between 300 and 6900 M. Crystallization of dimeric 1:1 and trimeric 1:2 and 2:1 complexes enabled an in-depth examination of these complexes in the solid state, proving the selection of the -B(OH) syn-syn conformer through a pair of frontal H-bonds with the relevant AA partner. Non-ortho-substituted boronic acids result in "flat" complexes. On the other hand, sterically demanding analogues bearing ortho substituents strive to retain their recognition properties by rotation of the ArB(OH) moiety, forming "T-shaped" complexes. Solid-state studies of a diboronic acid and a tetraazanaphthacene provided for the first time the formation of a supramolecular H-bonded polymeric ribbon. On the basis of the conformational dynamicity of the -B(OH) functional group, it is expected that these findings will also open new possibilities in metal-free catalysis or organic crystal engineering, where double-H-bonding donor boronic acids could act as suitable organocatalysts or templates for the development of functional materials with tailored organizational properties.

Cyclic diaryl ethers are present in multiple natural compounds, organic pollutants as well as in π-conjugated organic molecular materials. This short review aims at overviewing the main synthetic advances in the O-annulation methods for preparing five-, six-, and seven-membered rings through C–H cleavage.1 Introduction2 Five-Membered Rings: The Dibenzofuran (DBF) Motif2.1 Palladium-Catalysed C–H Activation2.2 Copper-Catalysed C–H Activation2.3 Non-CH Activation Oxidant-Mediated Cyclisation2.4 Light-Mediated Cyclisation2.5 Acid-catalysed C–O Cleavage/C–O Formation3 Six-Membered Rings: DBX, PXX, Xanthone, and Their Derivatives3.1 Dibenzoxanthene (DBX)3.2 Peri-Xanthenoxanthene (PXX)3.3 Xanthones3.4 Miscellaneous4 Seven-Membered Rings: Cularine5 Conclusion

Through application of an external magnetic field upon jellification of PHBV polymer in different solvents, an anisotropic organogel is obtained. This material presents two alignment steps in an external magnetic field, in the liquid phase and during the jellification, both phenomena measured by magnetic field induced linear birefringence. Remarkably, the organogel developed in this study presents a strong level of birefringence, 80 % of its maximum, in an external magnetic field as low as 2 T resulting from the magnetic alignment of the fibres of the material. This anisotropic material shows changes of absorbance upon rotation of a polarizer switching from transparent to opaque .)n addition, its suprastructure does not influence the luminescent properties of encapsulated chromophores, allowing the formation of coloured anisotropic materials.