Valerii Z. Shirinian

Copper(II)-Mediated Aerobic Synthesis of Imidazo[1,2-a]pyridines via Cascade Aminomethylation/Cycloisomerization of Alkynes.

A single copper(II)-catalyzed three-component cascade aminomethylation/cycloisomerization of propiolates to form imidazo[1,2-a]pyridines was explored. A straightforward method was developed for the practical synthesis of functionalized imidazo[1,2-a]pyridines from benzaldehydes, 2-aminopyridines, and propiolate derivatives catalyzed by Cu(OAc)2 hydrate in the presence of air. The protocol is marked by excellent yields, functional group tolerance, and, above all, adaptability to synthesize imidazo[1,2-a]pyridine-based drug molecules such as Alpidem.

Photoinduced skeletal rearrangement of diarylethenes comprising oxazole and phenyl rings.

A novel photochemical rearrangement of diarylethenes bearing oxazole and benzene derivatives as aryl moieties that results in the formation of polyaromatic systems was investigated. The mechanism of the transformation includes photocyclization, sequential [1,9] and [1,3]-hydrogen shifts, as well as a lateral oxazole ring-opening process. It was shown that this reaction can be an effective synthetically preparative method for the preparation of naphthalene (polyaromatic) derivatives.

Merocyanines: Synthesis and Application

The rapid progress of information technology continues to stimulate the exploration of innovative materials and architectures for digital processing. Merocyanine dyes appear to be potential candidates for the realization of future data-elaboration, -storage, and -communication devices. While the early stages of this research have been mainly concerned with applications in the fields of photography and medicine, most of the current work on these dyes involves investigation of moderate-to-large intermolecular aggregates, including both red-shifted “J” and blue-shifted “H” aggregates, optical and fluorescent sensors, and applications in solar engineering and medicine. This review summarizes advances in the synthesis, structure, and applications of merocyanine dyes over the last decade.

General Photoinduced Sequential Electrocyclization/[1,9]-Sigmatropic Rearrangement/Ring-Opening Reaction of Diarylethenes.

A novel and efficient photochemical transformation of diarylethenes comprising a five-membered heterocyclic ring and phenyl moiety is described. This reaction provides a simple method for the preparation of functionalized naphthalene derivatives via photorearrangement reaction of diarylethenes, and the process is characterized by high efficiency that was determined by NMR monitoring. Some mechanistic aspects of this process have been also explored. It was found that the reaction includes tandem transformation of three basic processes: the photocyclization of the hexatriene system, [1,9]-sigmatropic rearrangement, and heterocyclic ring opening. Diarylethenes with different heterocycle moieties (thiophene, benzo[b]thiophene, furan, indole, imidazole, thiazole, oxazole, pyrazole) have been involved into this process, and the target naphthalenes with good yields have been obtained. The opportunity for use in the transformation of diarylethenes with different heterocyclic residues permits synthesis of naphthalenes with desired functional groups. The general character and high efficiency of the reaction promise that the transformation can be an effective synthetic route for the annulation of benzene rings to various aromatic systems, including heterocycles.

Photochromic dihetarylethenes. 14. Synthesis of symmetrical and unsymmetrical dihetarylcyclobutene-1,2-diones

A procedure was developed for the synthesis of symmetrical and unsymmetrical cyclobutene-1,2-dione derivatives bearing thiophene and thieno[3,2-b]thiophene substituents by the Friedel—Crafts reaction of the corresponding heterocyclic compounds with squaric acid dichloride in the presence of AlCl3. In addition to the target dihetarylcyclobutenediones, monoacylation products of methyl (2,5-dimethylthiophen-3-yl)acetate and methyl 5-methylthieno[3,2-b]thiophene-2-carboxylate with squaric acid dichloride were isolated and characterized.

A comparative study of the spectral and kinetic properties of photochromic dihetarylethenes based on maleic anhydride and maleimide

A comparative spectral-kinetic study of the photochromism of a number of new thermally irreversible 1,2-diarylethenes, considered as possible candidates for 3D optical data storage, is performed. The diarylethenes studied contain as bridges either maleic anhydride or maleimide derivatives. A relation between the structure of the bridges and substituents of these compounds and their photochromic properties is established.

Structural and Spectral Properties of Photochromic Diarylethenes: Size Effect of the Ethene Bridge

The effect of the size of the ethene bridge on the structural and spectral properties of photochromic diarylethenes, which remains a poorly understood phenomenon, was studied as applied to diarylethenes containing unsymmetrical (cyclohexenone and cyclopentenone) and symmetrical (cyclohexene and cyclopentene) ethene bridges. Thiophene, oxazole, and imidazole derivatives were used as aryl moieties. An increase in the size of the ethene bridge in the cycloalkenone series was found to be accompanied by a hypsochromic shift of the absorption maximum of the photoinduced form, whereas no difference was found for cycloalkenes. A detailed analysis of the NMR spectra (including 2D experiments) revealed previously unknown effects associated with the existence of an intramolecular hydrogen bond (CH···N) between the six-membered ethene bridge and the azole substituents. The NMR experimental data obtained were confirmed by DFT quantum chemical calculations and X-ray analysis. It was found that an intramolecular hydrogen bond favors an increase of the quantum yield of the photocyclization reaction.

New thermally stable photochromic di(het)arylethenes of the cyclopentenone series

Oxidation of 2,3-diarylcyclopent-2-en-1-ones with m-chloroperoxybenzoic acid gave new thermally stable sulfone derivatives of photochromic diarylethenes. The spectral properties of the compounds obtained (the wavelengths of the maxima of the absorption bands of their initial and cyclic forms, the quantum yields of photocyclization and photobleaching reactions) as well as their thermal stability and fatigue resistance were examined. The relationship between the structures of the synthesized compounds and their photochromic properties was determined. The energy differences between the ground-state molecules of the starting and photoinduced isomers of 2,3-diarylcyclopent-2-en-1-ones were calculated by the DFT/B3LYP1 method with the 6-31G(d) basis set. The calculated energy differences can be used to predict and explain such spectral characteristics of photochromic diarylethenes as the thermal stability of photoinduced isomers and the quantum yields of cycloreversion reactions.

Photochromic dihetarylethenes. 13. Optimization of conditions for the acylation of 2,5-dimethylthiophene with squaric acid dichloride

The conditions for acylation of 2,5-dimethylthiophene with squaric acid dichloride were optimized, and 3,4-bis(2,5-dimethylthiophen-3-yl)cyclobut-3-ene-1,2-dione was obtained in good yield. X-ray diffraction analysis demonstrated that the by-product has the structure of 1a,1b-dichloro-5-(2,5-dimethylthiophen-3-yl)-3-hydroxy-4,5a-dimethyl-1b,4a,5,5a-tetrahydro-1aH-1-thiacyclopropa[a]pentalen-2-one.

Facile synthesis of photoactive diaryl(hetaryl)cyclopentenes by ionic hydrogenation

A facile synthetic approach to photoactive diarylethenes comprising a cyclopentene ring as an ethene bridge was developed based on reduction of 2,3-diaryl(hetaryl)cyclopent-2-en-1-ones through an ionic hydrogenation reaction. The method provides access to unsymmetrical photoswitchable diarylethenes containing benzene, thiophene, or azoles (thiazole, oxazole, imidazole) as aromatic moieties in 40–71% yields. Diarylethenes comprising two heterocyclic moieties show typical photochromic properties, with absorption maxima of the photoinduced form in the blue region (yellow photochromes).