Recent advances in sustainable bio-based furanic materials are highlighted with a focus on structural and functional diversity, connected to practical applications of both linear and branched polymer types.

This work reveals ambident nucleophilic reactivity of imidazolium cations towards carbonyl compounds at the C2 or C4 carbene centers depending on the steric properties of the substrates and reaction conditions. Such an adaptive

2-Azidomethyl-5-ethynylfuran, a new ambivalent compound with both azide and alkyne moieties that can be used as a self-clickable monomer, is synthesized starting directly from renewable biomass. The reactivity of the azide group linked to furfural is tested via the efficient preparation of a broad range of furfural-containing triazoles in good to excellent yields using a 'green' copper(I)-catalyzed azide-alkyne cycloaddition procedure. Access to new bio-based chemicals and oligomeric materials via a click-chemistry approach is also demonstrated using this bio-derived building block.

C−H functionalization is one of the most convenient and powerful tools in the arsenal of modern chemistry, deservedly nominated as the “Holy Grail” of organic synthesis. A frequent disadvantage of this method is the need for harsh reaction conditions to carry out transformations of inert C−H bonds, which limits the possibility of its use for modifying less stable substrates. Biomass‐derived furan platform chemicals, which have a relatively unstable aromatic furan core and highly reactive side chain substituents, are extremely promising and valuable organic molecules that are currently widely used in a variety of research and industrial fields. The high sensitivity of furan derivatives to acids, strong oxidants, and high temperatures significantly limits the use of classical methods of C−H functionalization for their modification. New methods of catalytic functionalization of non‐reactive furan cores are urgently required to obtain a new generation of materials with controlled properties and potentially bioactive substances.

An efficient strategy was developed for directing-group-free C–H functionalization of biomass-derived C6 furanic building block. Palladium-catalyzed C–H functionalization of the low-reactive C3 position was successfully performed in 2,5-diformylfuran, an important derivative of the biobased platform chemical 5-(hydroxymethyl)­furfural. The ligand-free catalytic arylation was carried out without using protecting or directing groups, which is of key importance for the studied area to achieve waste-minimized and step-economic biomass processing. The experimental results combined with density functional theory calculations revealed a reaction mechanism and indicated that the presence of the aldehyde group is essential for catalytic reaction. Enolization of the aldehyde group and Pd binding play an important role in governing the overall C–H functionalization pathway. One of the obtained arylated furanic compounds was tested as a model substrate for reduction and oxidation of carbonyl groups to highlight its versatile synthetic potential.

The analysis of products synthesized by Cu-catalyzed click reactions can be complicated due to the presence of metal impurities in isolated substances, which may "selectively" distort some signals in NMR spectra. Such a pronounced impurity effect was found in both 1 H and 13 C NMR spectra for a number of 1,4-substituted 1,2,3-triazoles. Recording of the full undistorted spectra is possible with additional product treatment, with more thorough purification, or by recording the spectra at low temperatures. The reasons for the distortion and disappearance of signals have been thoroughly studied; it was shown that impurities of paramagnetic metal ions in small amounts lead to this effect. Here, we want to deliver a warning message to the community: when all NMR signals in a spectrum are distorted, this situation is easy to detect. However, if only a few signals are "selectively" removed by impurities and the rest of the spectrum appears normal, this situation is much harder to notice. Therefore, incorrect conclusions about chemical structure may be obtained. Here, we demonstrated the example of Cu 2+ ions, but one may anticipate a similar effect for other paramagnetic metal contaminants if the organic molecule has a functional group capable of coordination (heteroatom or a multiple bond).

Ambident nucleophilic reactivity of imidazolium cations at the C2 and C4 carbene centers indicated the dynamic nature of imidazolium‐based organocatalysis proceeding by means of a covalent interaction of imidazolium carbenes with carbonyl substrates and was explained by the generation of the H‐bonded ditopic carbanionic carbenes along with the classical C2 carbenes. Based on these findings, covalent bonding of imidazolium carbenes with carbonyl group of enolizable ketones was investigated. More information can be found in the Full Paper by K. Galkin, B. Karlinskii, V. P. Ananikov, et al. on page 8567.

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