Vladimir Iashin

Regioselective modifications of cellulose using activated cellulose derivatives such as 6‐halo‐6‐deoxycelluloses provide a convenient approach for developing sustainable products with properties tailored to specific applications. However, maintaining precise regiochemical control of substituent distribution in 6‐halo‐6‐deoxycelluloses is challenging due to their insolubility in most common solvents and the resulting difficulties in precise structure elucidation by modern instrumental analytical techniques. Herein, an accessible NMR‐based approach toward detailed characterization of 6‐halo‐6‐deoxycelluloses, including the determination of the degrees of substitution at carbon 6 (DS₆), is presented. It is shown that the direct‐dissolution cellulose solvent, tetrabutylphosphonium acetate:DMSO‐d₆, converts 6‐halo‐6‐deoxycelluloses to 6‐monoacetylcellulose, enabling in situ solution‐state NMR measurements. A range of 1D and 2D NMR experiments is used to demonstrate the quantitivity of the conversion and provide optimum dissolution conditions. In comparison with other NMR‐based derivatization protocols for elucidating the structure of 6‐halo‐6‐deoxycelluloses, the presented approach offers major advantages in terms of accuracy, speed, and simplicity of analysis, and minimal requirements for reagents or NMR instrumentation.

Nucleophilic ionic sources of fluoride are essential reagents in the synthetic toolbox to access high added-value fluorinated building blocks unattainable by other means. In this review, we provide a concise description and rationale of the outstanding features of one of these reagents, tetramethylammonium fluoride (TMAF), as well as disclosing the different methods for its preparation, and how its physicochemical properties and solvation effects in different solvents are intimately associated with its reactivity. Furthermore, herein we also comprehensively describe its historic and recent utilization, up to December 2021, in C-F bond-forming reactions with special emphasis on nucleophilic aromatic substitution fluorinations with a potential sustainable application in industrial settings, as well as its use as a base capable of rendering unprecedented transformations.

Organoboron compounds are essential reagents in modern C−C coupling reactions. Their synthesis via catalytic C−H borylation by main group elements is emerging as a powerful tool alternative to transition metal based catalysis. Herein, a straightforward metal‐free synthesis of aryldifluoroboranes from BF₃ and heteroarenes is reported. The reaction is assisted by sterically hindered amines and catalytic amounts of thioureas. According to computational studies the reaction proceeds via frustrated Lewis pair (FLP) mechanism. The obtained aryldifluoroboranes are further stabilized against destructive protodeborylation by converting them to the corresponding air stable tetramethylammonium organotrifluoroborates.

C‐6‐substituted thymidines are biochemically important compounds. The thymidine (6–4) photoproduct [i.e., 5‐hydroxy‐6‐(thymidine‐4‐yl) dihydrothymidine], in particular, is a DNA lesion that is triggered by the UV irradiation of sunlight. Herein, we report a metal‐freecis‐diastereoselective ring opening of thymidine 5,6‐epoxides by using mildly nucleophilic organofluoroborates in the presence of BF₃·Et₂O to provide facile access to (6–4) photoproduct analogues. A broad range of aryl and alkynylfluoroborates are compatible with the reaction conditions, which also tolerate various protecting groups. Furthermore, the epoxide addition products can undergo a thionyl chloride/pyridine promoted dehydration process to give the respective pharmaceutically attractive C‐6‐substituted thymidines in high yields, thus providing a new and straightforward method for their synthesis.

A sterically demanding amine, 1,2,2,6,6‐pentamethylpiperidine (PMP), forms a highly reactive Lewis acid–base pair with boron trifluoride. This pair reacts with terminal acetylenes to give the products of C(sp)−H borylation, previously unknown tri‐ and tetraalkynylboron compounds. Trialkynylfluoroborates can serve as surrogates of alkynyltrifluoroborates for C−C coupling reactions. Using aqueous NaOH, PMP can be recovered from its tetrafluoroborate salt, which is formed as a C−H borylation byproduct. Combining the discovered borylation reactivity with the PMP recovery provides a straightforward and atom‐efficient approach to synthetically useful alkynylfluoroborates.

In this study we have explored the influence of mutual position of chlorin electron donor and fullerene C₆₀ electron acceptor on photoinduced electron transfer. Two zinc-chlorin-aza-[18]crown-6 compounds and three pyrrolidino[60]fullerenes with alkyl aminium and varying coordinative moieties were synthesized and used for self-assembling of a set of complexes via two-point binding. The aza[18]crown6 moieties were connected to chlorins via amide linker either at 13⁴ or 17⁴ position, hence, being attached on different sides of the chlorin plane. Furthermore, in the former case, the linker holds the crown closely spaced, whereas, in the latter, the linker gives more space and conformational freedom for the crown with respect to the chlorin macrocycle. The coordinative moieties at fullerene site, 3-pyridine, 4-pyridine, and 3-furan, were built by utilizing the Prato reaction. The two-point binding drove the molecules into specific complex formation by self-assembling; aminium ion was chelated by crown ether, while zinc moiety of chlorin was coordinated by pyridine and furan. Such pairing resulted in distinct supramolecular chlorin-fullerene dyads with defined distance and orientation. The performed computational studies at DFT level in solution, with TPSS-D3/def2-TZVP//def2-SVP, indicated different geometries and binding energies for the self-assembling complexes. Notably, the computations pointed out that for all the studied complexes, the donor–acceptor distances and binding energies were dictated by chirality of pyrrolidino ring at C₆₀. The selective excitation of chlorin chromophore revealed efficient emission quenching in all dyads. The ultrafast spectroscopy studies suggested a fast and efficient photoinduced charge transfer in the dyads. The lifetimes of the charge separated states range from 55 to 187 ps in o-dichlorobenzene and from 14 to 60 ps in benzonitrile. Expectedly, the electron transfer rate was found to be critically dependent on the donor–acceptor distance; additionally, the mutual orientation of these entities was found to have significant contribution on the rate.

Chlorophyll derivatives were functionalized with a trifluoroamide (TFA) group to obtain colorimetric ion sensors. Prior to this, a NO₂BF₄*pyridine based, chlorin nitration method was developed. The base strength dependent sensing of AcO⁻, F⁻ and CN⁻ ions was detected in aqueous media, which was enhanced in nonprotic solvents by an integration of the ditopic chelation capable amine crown-6 moiety.