Current Organic Chemistry - Volume 26, Issue 1, 2022

In recent years, photoredox catalysis has appeared as a new paradigm for forging a wide range of chemical bonds under mild conditions using abundant reagents. This approach allows many organic transformations through the generation of various radical species, enabling the valorization of non-traditional partners. A continuing interest has been devoted to the discovery of novel radical-generating procedures. Over the last ten years, strategies using rare-earth complexes as either redox-active centers or as redox-neutral Lewis acids have emerged. This review provides an overview of the recent accomplishments made in this field. It especially aims to demonstrate the utility of rare-earth complexes for ensuring photocatalytic transformations and to inspire future developments.

The present review discusses a new viewpoint on refractometry as the oldest experimental physical method, whose scientific potential in the estimation of structural effects in organic chemistry has been missed so far. The author demonstrates that upon certain adjustment and redesign of refractometry, this potential can be tapped and successfully used to determine a type of π-electron interaction, delocalization degree of π-electrons in organic compounds, and to perform quantitative estimates of resonance effects in unsaturated, (polycyclic) aromatic, and other polyconjugated systems (e.g., fullerenes). The method for accurate separation of molar refraction into additive and constitutive components was suggested; the method is based on the specially developed additive scheme. It was revealed that the negative deviations from additivity for cycloalkanes depend linearly on the number of carbon atoms in the ring. Excellent linear correlations between renewed optical exaltations, the number of π-electrons in a conjugated system, and experimentally found resonance energy (determined from hydrogenation heat values) were demonstrated. Angular coefficients of the correlation series (ρ-constants) are considered as a criterion of classification, which characterizes the degree of mobility of π-electrons in the conjugated system of a given type. It is emphasized that the development of methods for precise measurement of the constitutive components of molar refraction may become a useful additional source of information about resonance and other effects in organic and polymer chemistry.

CO2 fixation reactions are of paramount interest both from economical and environmental perspectives. As an abundant, non-toxic, and renewable C1 feedstock, CO2 can be utilized for the synthesis of fuels and commodity chemicals under elevated reaction conditions. The major challenge in the CO2 utilization reactions is its chemical inertness due to high thermodynamic stability and kinetic barrier. The carboxylation of unsaturated hydrocarbons with CO2 is an important transformation as it forms high-value reaction products having industrial as well as medicinal importance. This mini-review is mainly focused on the recent developments in the homogeneously and heterogeneously catalyzed carboxylation of alkenes and alkynes by using carbon dioxide as a reagent. We have highlighted various types of carboxylation reactions of alkenes and alkynes involving different catalytic systems, which comprise mainly C-H bond activation, hydrocarboxylation, carbocarboxylation, heterocarboxylation, and ring-closing carboxylation, including visible-light assisted synthesis processes. The mechanistic pathways of these carboxylation reactions have been described. Moreover, challenges and future perspectives of these carboxylation reactions are discussed.

A new class of dendrimers with open-resorcinarenes has been synthesized in good yields (77-85%). The open-resorcinarenes showed a high capacity for functionalization, having eight hydroxyl groups. The Williamson reaction with N,N-bis(2-azidoethyl)-2-bromo acetamide did not show any steric effect, obtaining sixteen azide terminal groups, which gave us the possibility to obtain a high molecular weight dendrimer via the azide-alkyne click reaction with prop-2-yn-1-yl-(ibuprofen)L-serinate derivatives to obtain the triazole ring spacers and the L-serinate(ibuprofen) derivatives as terminal groups. Also, we carried out the deprotection reaction of the L-serinate moiety terminal groups of the dendrimer 10 in good yields (95%). Three novel open-resorcinarene den-drimers with sixteen ibuprofen-L-serinate derivatives and hydroxyl, tert-butyl, and carboxylic acid; therefore, with three different terminal groups, with possible nanomedical activity are reported.