Intra- and intermolecular Se...X (X = Se, O) interactions in selenium-containing heterocycles: 3-benzoylimino-5-(morpholin-4-yl)-1,2,4-diselenazole

Isoselenocyanates: Synthesis and Their Use for Preparing Selenium-Based Heterocycles

Isoselenocyanates (ISCs) are a class of organoselenium compounds that have been recognized as potential chemotherapeutic and chemopreventative agents against cancer(s) and infectious diseases. ISC compounds are chemically analogous to their isosteric relatives, isothiocyanates (ITCs); however, they possess increased biological activity, such as enhanced cytotoxicity against cancer cells. ISCs not only serve as significant products, but also as precursors and essential intermediates for a variety of organoselenium compounds, such as selenium-containing heterocycles, which are biologically active. While syntheses of ISCs have become less difficult to accomplish, the syntheses of selenium-containing heterocycles are often difficult due to the use of highly toxic selenium reagents. Because of this, ISCs can serve as versatile reagents for the preparation of these heterocycles. In this review, the classical and recent syntheses of ISCs will be discussed, along with notable and recent synthetic work employing ISCs to access novel selenium-containing heterocycles.

1 Introduction

1.1 Selenium and Health

2 Isoselenocyanates

2.1 Preparation of Isoselenocyanates

3 Selenium-Containing Heterocycles

3.1 Notable Synthetic Work

3.2 Recent Synthetic Work

3.2.1 Synthesis of N-(3-Methyl-4-phenyl-3H-selenazol-2-ylidene)benzamide­ Derivatives

3.2.2 Synthesis and X-ray Studies of Diverse Selenourea Derivatives

3.2.3 Synthesis of Heteroarene-Fused [1,2,4]Thiadiazoles/Selenadiazoles via Iodine-Promoted [3+2] Oxidative Cyclization

3.2.4 2-Amino-1,3-selenazole Derivatives via Base-Promoted Multicomponent Reactions

4 Conclusion

Zero-, one-, two- and three-dimensional supramolecular architectures sustained by Se…O chalcogen bonding: A crystallographic survey

The Cambridge Structural Database was evaluated for crystals containing Se…O chalcogen bonding interactions. These secondary bonding interactions are found to operate independently of complementary intermolecular interactions in about 13% of the structures they can potentially form. This number rises significantly when more specific interactions are considered, e.g. Se…O(carbonyl) interactions occur in 50% of cases where they can potentially form. In about 55% of cases, the supramolecular assemblies sustained by Se…O(oxygen) interactions are one-dimensional architectures, with the next most prominent being zero-dimensional assemblies, at 30%.

Synthesis of side-chain regioregular and main-chain alternating poly(bichalcogenophene)s and an ABC-type periodic poly(terchalcogenophene)

Three unsymmetrical diiodobichalcogenophenes SSeI2, STeI2, and SeTeI2 and a diiodoterchalcogenophene SSeTeI2 were prepared. Grignard metathesis of SSeI2, STeI2, SeTeI2, and SSeTeI2 occurred regioselectively at the lighter chalcogenophene site because of its relatively lower electron density and less steric bulk. Nickel-catalyzed Kumada catalyst-transfer polycondensation of these Mg species provided a new class of side-chain regioregular and main-chain AB-type alternating poly(bichalcogenophene)s-PSSe, PSTe, and PSeTe-through a chain-growth mechanism. The ring-walking of the Ni catalyst from the lighter to the heavier chalcogenophene facilitated subsequent oxidative addition, thereby suppressing the possibility of chain-transfer or chain-termination. More significantly, the Ni catalyst could walk over the distance of three rings (ca. 1 nm)-from a thiophene unit via a selenophene unit to a tellurophene unit-to form PSSeTe, the first ABC-type regioregular and periodic poly(terchalcogenophene) comprising three different types of 3-hexylchalcogenophenes.

Supramolecular insight into the substitution of sulfur by selenium, based on crystal structures, quantum-chemical calculations and biosystem recognition

Statistical analysis of data from crystal structures extracted from the Cambridge Structural Database (CSD) has shown that S and Se atoms display a similar tendency towards specific types of interaction if they are part of a fragment that corresponds to the side chains of cysteine (Cys), methionine (Met) selenocysteine (Sec) and selenomethionine (Mse). The most numerous are structures with C-H...Se and C-H...S interactions (∼80%), notably less numerous are structures with Se...Se and S...S interactions (∼5%), and Se...π and S...π interactions are the least numerous. The results of quantum-chemical calculations have indicated that C-H...Se (∼-0.8 kcal mol^-1) and C-H...S interactions are weaker than the most stable parallel interaction (∼-3.3 kcal mol^-1) and electrostatic interactions of σ/π type (∼-2.6 kcal mol^-1). Their significant presence can be explained by the abundance of CH groups compared with the numbers of Se and S atoms in the crystal structures, and also by the influence of substituents bonded to the Se or S atom that further reduce their possibilities for interacting with species from the environment. This can also offer an explanation as to why O-H...Se (∼-4.4 kcal mol^-1) and N-H...Se interactions (∼-2.2 kcal mol^-1) are less numerous. Docking studies revealed that S and Se rarely participate in interactions with the amino acid residues of target enzymes, mostly because those residues preferentially interact with the substituents bonded to Se and S. The differences between Se and S ligands in the number and positions of their binding sites are more pronounced if the substituents are polar and if there are more Se/S atoms in the ligand.

New insight into the chemistry of selenoureas: synthesis and single crystal structural study of diverse derivatives

A series of new heteroatom derivatives of N-acylselenoureas was obtained through the reaction of KSeCN with acyl chloride and primary amines, followed by the cyclisation reaction with phenacyl bromides.

Diverse Derivatives of Selenoureas: A Synthetic and Single Crystal Structural Study

Reacting aroyl chlorides with an equivalent of potassium selenocyanate, followed by treating with an equivalent of 1,2,4-tri-tert-butylaniline at room temperature, resulted in the expected selenoureas and unusual diselenazoles. The selenation of selenourea by Woollins Reagent gave a new selenoformamide. Nucleophilic addition of selenoureas with acyl bromides led to the formation of new carbamimidoselenoates rather than the expected 1,3-selenazoles. The novel compounds prepared were characterised spectroscopically and crystallographically.

Crystal structure of 1-{2-[(2-meth-oxy-phen-yl)selan-yl]phen-yl}-4-phenyl-1H-1,2,3-triazole

In the title compound, C21H17N3OSe, the dihedral angles between the central five-membered ring and the C- and N-bound rings are 17.89 (10) and 42.35 (10)°, respectively, indicating the mol-ecule is twisted. The dihedral angle between the Se-bound rings is 85.36 (10)°. A close intra-molecular Se⋯O contact of 2.8507 (13) Å is noted. In the crystal, C-H⋯O, C-H⋯N and C-H⋯π inter-actions lead to the formation of supra-molecular layers parallel to (011); these stack with no specific inter-molecular inter-actions between them.