The review describes the history of the development of adamantane chemistry and shows moments that stimulated rise in the studies, as well as the main lines of research in this field and prospects thereof, on the basis of published data (up to 2024) with an emphasis on the last two decades.

Разработаны методы синтеза симметричных 1,3-ди(3-R-1-адамантил)ацетонов [R = ОН, арен, гетероарен, NHCOR1, NHC(S)NH2] на основе реакции CF3SO3H/(CF3CO)2O-катализируемого самоацилирования 3-гидрокси-1-адамантилуксусной кислоты.

The IR spectra of calix[6]arenes with adamantylacetic acid (1) and adamantyl (2) substituents along the upper rim of the molecule were studied. It was shown that the formation of an intramolecular H-bond between carboxyl groups on the upper rim of the calix[6]arene molecules with adamantylacetic acid fragments does not weaken the cyclic cooperative H-bond at the lower rim of the macrocycle, which is confirmed by DFT calculations. The calculation has shown that molecules 1 and 2 take on the conformation of a compressed cone. The reactivity of adamantylcalix[6]arenes changes due to the association of carboxyl groups. The formation of dimeric complexes due to H-bonds of carboxyl groups along the upper rim of molecule 1 does not lead to a noticeable redistribution of the charges of hydroxyl groups on the lower rim. Heating a sample of 1 to a temperature of 180 degrees C destroys a small part of the H-bonds between neighboring carboxyl groups, as evidenced by the appearance of a weak band at 3535 cm(-1). However, after cooling to room temperature, the H-bonds between the carboxyl groups are restored. Heating up to 355 degrees C-leads to irreversible changes in the H-bonding system, but even at this temperature, structure destruction has not been observed. (C) 2021 Elsevier B.V. All rights reserved.

Methods have been developed for the synthesis of symmetrical 1,3-bis(3-R-adamantan-1-yl)­acetones [R = OH, aryl, heteroaryl, R′C(O)NH, NH 2 C(S)NH] by CF 3 SO 3 H/(CF 3 CO) 2 O-catalyzed self-acylation of 2-(3-hydroxyadamantan-1-yl)acetic acid.

The adamantylation of adenine and N-6-methyl- and N-6,N-6-dimethyladenines with 3-R-adamantan-1-ols (R = H, iso-Pr, CH2COOH, uracil-5-yl) in trifluoroacetic acid gave of 9-(3-R-adamantan-1-yl)adenines. The structures of 9-(adamantan-1-yl)- and N-6-methyl-9-(adamantan-1-yl)adenines were proved by XRD analysis.

5-[3(4)-R-Adamantan-1-yl]salicylic acids [R = H, Alk, Ar, OH, NHC(S)NH2] have been synthesized by electrophilic substitution reactions of hydroxy- and bromoadamantanes with salicylic acid, as well as by reactions of 5-(3-hydroxyadamantan-1-yl)salicylic acid with carbon and nitrogen nucleophiles, in trifluoroacetic acid. The possibility of selective hydroxylation of the adamantane fragment in 5-(adamantan-1-yl)salicylic acid with sulfuric acid in trifluoroacetic anhydride has been demonstrated.

The IR spectra of p-(3-carboxy-1-adamantyl)thiacalix[4]arene (1) were studied. IR spectra of compound 1 do not contain bands of free hydroxyl groups. The νOH value at 3377 cm-1 signifies the formation of an intramolecular H-bond along the lower edge of compound 1. It was found that all the studied calixarene derivatives containing adamantylcarboxylic acid fragments on the upper edge form H-bonds between adjacent carboxyl groups. At the top edge of thiacalixarene, carboxyl groups form dimers or cyclic tetramers through intramolecular H-bonds. The conformation of the cone is preserved, but there is a mutual influence of Hbonds along the lower and upper edges of the thiacalixarene molecules. A structure with dimeric H-bonds between carboxyl groups is 1.5 kJ/mol less preferable than the conformation with tetrameric cyclic H-bonds of compound 1. Comparison of the νOH absorption frequency of alcohol hydroxyl groups in IR spectra of thiacalixarenes shows that the presence of the second H-bond system weakens the H-bonds of alcohol hydroxyl groups slightly.

The IR spectra of p-(3-carboxy-1-adamantyl)thiacalix[4]arene (1-AdCOOHTC4A) have been studied. IR spectra of crystalline 1-AdCOOHTC4A obtained at room temperature or upon heating to 250 °C or its dilute solutions lack bands of free hydroxyl groups. The frequency of hydroxyl groups at 3377 cm−1 indicates the formation of an intramolecular H-bond along the lower rim of the 1-AdCOOHTC4A molecule. On the top edge of thiacalixarene, the carboxyl groups form dimeric or cyclic tetrameric complexes via intermolecular H-bonds. The conformation of the cone persists, but there is a mutual influence of H-bonds along the upper and lower rims of the thiacalix[4]arene molecule. The structure with dimer H-bonds between carboxyl groups is 31.9 KJ/mol less preferable than the conformation with tetramer cyclic H-bonds for 1-AdCOOHTC4A. Comparison of the absorption band of νOH alcohol hydroxyl groups in the IR spectra of 1-AdCOOHTC4A at 3377 cm−1, with the corresponding band of 1-AdTC4A at 3372 cm−1, suggests that the presence of the second system of H-bonds of carboxyl groups in the first molecule does not affect the H-bond of alcohol hydroxyl groups.

The IR and Raman spectra of p-(3-carboxymethyl-1-adamantyl)calix[4]arene (1) and tetrapropoxy-p-(3carboxymethyl-1-adamantyl)calix[4]arene (2) were studied. In the IR spectra of crystals and solutions of calixarenes, there is no band of stretching vibrations of free OH groups. In the IR spectrum of compound 1 in the crystalline state, an intense wide band is observed at 3187 cm & minus;1. In the IR spectrum of a dilute solution in CCl4, this band shifts to 3118 cm & minus;1. The carboxyl groups form cyclic dimer or tetramer complexes.& nbsp; The formation of dimers of carboxyl groups is more favorable than for cyclic tetramers. The energy difference is 33.8 and 53.0 kJ/mol in compounds 1 and 2, respectively. The calculation showed that molecules 1 and 2 of dimeric and tetrameric complexes assume the cone conformation. The molecules of compound 2 are in the cone conformation even in the absence of hydrogen bonds along the lower rim.& nbsp; (c) 2021 Elsevier B.V. All rights reserved.

Trifluoroacetic anhydride was used as an efficient activator of the acylation of aryl methyl ketones with carboxylic acids in the presence of Brønsted and Lewis acids (SF3SO3H, MeSO3H, 4-MeC6H4SO3H·H2O, BF3·Et2O). In all cases, the products were the corresponding β-diketones. In the reactions in the presence of boron trifluoride–diethyl ether complex, the products were isolated as BF2-chelates with high yields.

A rapid and efficient method for ‘one-pot’ synthesis of pyrazoles from (hetero)arenes and carboxylic acids via successive formation of ketones and β-diketones followed by heterocyclization with hydrazine has been developed.

The IR spectra of p-(3-carboxy-1-adamantyl)-calix[4]arene (AdC4A) were studied. Using IR spectroscopy, it has been shown that in calixarene in dilute solution in CCl4, there was no free hydroxyl absorption band. The hydroxyl group band was characterized by a very low frequency, which indicates a strong intramolecular hydrogen bond on the lower rim of the calixarene molecules. On the upper rim of the calixarene, the carboxyl groups form cyclic dimer or tetramer complexes via intermolecular hydrogen bonds. The cone conformation persists, but there is a mutual influence of the hydrogen bonds along the top and bottom rims of the calixarene molecule. The structure with dimeric hydrogen bonds between the carboxyl groups is 16.5 KJ/mol more preferable than the structure with tetrameric cyclic hydrogen bonds for AdC4A. The reactivity depends on the type of association on the upper rim, whether these are hydrogen-bonded dimers or cyclic tetrameric association.

Despite the various attractive properties of γ-pyrones, there are still some deficiencies in their synthetic approaches such as lower atom economy, multistep processes, and prefunctionalization of the reagents. In this work, an efficient and simple (CF3CO)2O/CF3SO3H-mediated “one-pot” approach was realized to produce γ-pyrones by applying aromatic ketones/heteroarenes and carboxylic acids as the starting materials. The target products were isolated in moderate to excellent yields. The reaction mechanism was studied by density functional theory calculational methods. The results of experimental and theoretical investigations not only helped us explain the reason of high selectivity formation of β-diketones but also proved that 1,3,5-ketones might be important intermediates for the cyclization to afford γ-pyrones.

The hydrogen bonds and the conformations of calix[8]arene molecules with p-tert-butyl and p-1-adamantyl substituents were studied by infrared spectroscopy in different states. The conformations, the reactivity, the charge distribution and the IR spectra of the calixarenes were calculated by the DFT method with the PBE functional and a TZVP basis set. We compare the IR spectra of calix[8]arene molecules in the conformation of the pleated loop and the chair. The optimized geometry of the molecules reproduces the experimental X-ray data. The conformation chair is 20 kcal/mol less preferable than the conformation pleated loop. The conformation of a pleated loop is the most stable in the solid state and solution. Hydrogen bonds determine the stability of this structure. In the p-1-adamantylcalix[8]arene, stronger hydrogen bonds are realized compared to p-tert-butylcalix[8]arene. The observed IR spectra were interpreted using the calculated potential energy distribution with the quantum-chemical force constants. The theoretical absorption curves calculated for the pleated loop conformation correspond to the experimental IR spectra of the calix[8]arenes.

Thiacalix [4]arene (TC4A), p-tert-butylthiacalix [4]arene (t-BuTC4A) and p-(1-adamantyl)thiacalix [4] arene (1-AdTC4A) IR spectra were studied. Calculated energies and IR spectra of the various conformers (cone, partial cone, 1,2-alternate, and 1,3-alternate) were compared. The cone is the most stable conformation for all studied thiacalix [4]arenes. Theoretical IR spectrum of adamantylthiacalix [4]arene molecule in the form of a cone is consistent with experiment. Classification of bands in the IR spectrum of adamantylthiacalix [4]arene has been implemented. The strength of H-bonding in the thiacalix [4] arenes depends on the type of the substituent. In the conformation of the cone cyclic system of H-bonds are implemented for all the studied thiacalix [4]arenes. Introduction of adamantyl substituents leads to convergence of oxygen atoms in molecules of thiacalix [4]arene and H-bonds are strengthened. Conformation cone of molecules of thiacalix [4]arenes does not change when heated to a temperature of 180 degrees C and dissolving in a neutral solvent. (C) 2018 Elsevier B.V. All rights reserved.

The IR spectra of p-tertbutylcalix[6]arene and adamantylcalix[6]arenes were investigated. The influence of heating and dissolution on the system of hydrogen bonds in calix[6]arenes was studied. The theoretical IR spectrum of adamantylcalix[6]arene in the conformation of a compressed cone agrees with experiment. Classification of bands in IR spectrum of adamantylcalix[6]arene was performed. Structure and strength of the H-bonding in calix[6]arenes depends on the type of substituent. In all calix[6]arenes studied, the cyclic H-bonds in the conformation of the compressed cone is realized. Under the action of adamantyl substituents, there is a convergence of oxygen atoms in the calix[6]arene molecules and the strengthening of H-bonds. Heating to a temperature of 180 degrees C and the dissolution of calix[6]arenes in neutral solvents does not lead to a change in their conformation. (C) 2018 Elsevier B.V. All rights reserved.

The review summarizes and analyzes data on unusual transformations of camphor and its derivatives, reported in the past 20 years. The results of studying biological activity of compounds containing a camphor fragment are also given.

Biological test results for a series of adamantane-containing pyrimidines, purines, and their derivatives that were synthesized and studied in 1999 – 2001 are reviewed.