Synthesis of Thiol, Selenol, and Tellurol Esters by the Reaction of Organochalcogeno Mercurials with Acid Chlorides

Synthesis of Selenium Derivatives using Organic Selenocyanates as Masked Selenols: Chemical Reduction with Rongalite as a Simpler Tool to give Nucleophilic Selenides

The chemical reduction within a family of organic selenocyanates, as masked selenols, using reducing agents, such as Rongalite, sodium dithionite, and sodium thiosulfate is investigated. Using Rongalite, the corresponding diselenides were obtained quantitatively and selectively in very good to excellent yields (51-100 %) starting from alkyl, aryl, and benzyl selenocyanates. The scope of the reaction is unaffected by the electronic nature of the substituents. Furthermore, the reducing agent, Rongalite, is compatible with hydrolysable and reducing-sensitive functional groups. Additionally, a simple methodology employing the in-situ generated benzyl selenolate anion (PhCH2Se-) to promote aliphatic nucleophilic substitution, epoxide ring opening, and Michael addition reactions has been developed; thus, extending the structural diversity of the synthesized selenium derivatives.

Metal-free synthesis of selenoesters directly from carboxylic acids using bifunctional selenoureas under batch and continuous-flow conditions

A new metal-free method for the synthesis of selenoesters directly from carboxylic acids in a flow reactor is reported. The carboxylic acids, Michael acceptors, and bifunctional selenoureas (source of selenium and nucleophile, activator of carbonyl group) were reacted to obtain selenoesters (up to 70% yield). An evidence-backed plausible mechanism is also presented.

Palladium-Catalyzed Carbonylative Synthesis of Aryl Selenoesters Using Formic Acid as an Ex Situ CO Source

A new catalytic protocol for the synthesis of selenoesters from aryl iodides and diaryl diselenides has been developed, where formic acid was employed as an efficient, low-cost, and safe substitute for toxic and gaseous CO. This protocol presents a high functional group tolerance, providing access to a large family of selenoesters in high yields (up to 97%) while operating under mild reaction conditions, and avoids the use of selenol which is difficult to manipulate, easily oxidizes, and has a bad odor. Additionally, this method can be efficiently extended to the synthesis of thioesters with moderate-to-excellent yields, by employing for the first time diorganyl disulfides as precursors.

Synthetic Approaches to Selenoesters

Selenoesters are compounds of great synthetic relevance since they can be used in several types of chemical transformations and mainly due to their great capacity in the formation of acyl radicals. Therefore, the scientific community has been developing several methods for the synthesis of this class of molecules. This review will address the synthesis of these compounds from different starting materials, such as carboxylic acids derivatives (acid chlorides and anhydrides), aldehydes, selenoacetylenes and miscellaneous methods.

Selenolesterase enzyme activity of carbonic anhydrases

Carbonic anhydrases (CAs, E.C. 4.2.1.1) are metalloenzymes expressed on a variety of cell types. Their overexpression leads to serious pathologies, including cancer. The discovery of a series of selenolesters with high structural diversity as novel CA inhibitors is reported here. These compounds show remarkable in vitro inhibition against a panel of human CA isoforms such as hCA I, II, IX and XII. We observed that they undergo a CA mediated hydrolysis, releasing different active selenol fragments, which act as CA inhibitors. Notably, to the best of our knowledge, this is the first example of an enzyme with selenolesterase activity. In addition, X-ray crystallographic data support the proposed mechanism, proving selenolesters as novel pro-drug inhibitors with potential pharmacological applications.

Reductive Cleavage of the Se–Se Bond in the Presence of a Zn/AlCl3 System: Synthesis of Selenol Esters

Selenol esters were prepared in good yields by reacting diselenides with carboxylic acid anhydrides in dry acetonitrile in the presence of a Zn/AlCl3 system.

Redox-Neutral Synthesis of Selenoesters by Oxyarylation of Selenoalkynes under Mild Conditions

An approach for the mild synthesis of selenoesters starting from selenoalkynes through an acid-catalyzed, redox-neutral oxyarylation reaction is reported. Brønsted acid activation of a selenoalkyne leads to a selenium-stabilized vinyl cation, which is captured by an aryl sulfoxide and undergoes sigmatropic rearrangement to deliver the final α-arylated selenoester product. Computational studies have been carried out to elucidate the nature of the Se-stabilized carbocation.

Atom Efficient Preparation of Zinc Selenates for the Synthesis of Selenol Esters under "On Water" Conditions

We describe here an atom efficient procedure to prepare selenol esters in good to excellent yields by reacting [(PhSe)₂Zn] or [(PhSe)₂Zn]TMEDA with acyl chlorides under "on water" conditions. The method is applicable to a series of aromatic and aliphatic acyl chlorides and tolerates the presence of other functionalities in the starting material.

Polyethylene glycol-400/H3PO2: an eco-friendly reductive system for the synthesis of selanylesters

An alternative green method was described for the synthesis of selanylesters by reactions of acyl chlorides with arylselenols, generated in situ by reaction of diaryl diselenides with hypophosphorous acid (H₃PO₂) using polyethylene glycol-400 (PEG-400) as the solvent.

New polydentate trimethylsilyl chalcogenide reagents for the assembly of polyferrocenyl architectures

A series of polychalcogenotrimethylsilane complexes Ar(CH2ESiMe3)n, (Ar = aryl; E = S, Se; n = 2, 3, and 4) can be prepared from the corresponding polyorganobromide and M[ESiMe3] (M = Na, Li). These represent the first examples of the incorporation of such a large number of reactive -ESiMe3 moieties onto an organic molecular framework. They are shown to be convenient reagents for the preparation of the polyferrocenylseleno- and thioesters from ferrocenoyl chloride. The synthesis, structures, and spectroscopic properties of the new silyl chalcogen complexes 1,4-(Me3SiECH2)2(C6Me4) (E = S, 1; E = Se, 2), 1,3,5-(Me3SiECH2)3(C6Me3) (E = S, 3; E = Se, 4) and 1,2,4,5-(Me3SiECH2)4(C6H2) (E = S, 5; E = Se, 6) and the polyferrocenyl chalcogenoesters [1,4-{FcC(O)ECH2}2(C6Me4)] (E = S, 7; E = Se, 8), [1,3,5-{FcC(O)ECH2}3(C6Me3)] (E = S, 9; E = Se, 10) and [1,2,4,5-{FcC(O)ECH2}4(C6H2)] (E = S, 11 illustrated; E = Se, 12) are reported. The new polysilylated reagents and polyferrocenyl chalcogenoesters have been characterized by multinuclear NMR spectroscopy ((1)H, (13)C, (77)Se), electrospray ionization mass spectrometry and, for complexes 1, 2, 3, 4, 7, 8, and 11, single-crystal X-ray diffraction. The cyclic voltammograms of complexes 7-11 are presented.

Iron-catalyzed synthesis of thioesters from thiols and aldehydes in water

The preparation of thioesters through the iron-catalyzed coupling reaction of thiols with aldehydes is described. The reactions were carried out by using tert-butyl hydroperoxide (TBHP) as an oxidant and water as a solvent in most cases. This system is compatible with a variety of functional groups.

Syntheses of selenoesters through C–H selenation of aldehydes with diselenides under metal-free and solvent-free conditions

A DTBP-promoted C–H selenation of aldehydes with diselenides under metal-free and solvent-free conditions is described.

Syntheses of thiol and selenol esters by oxidative coupling reaction of aldehydes with RYYR (Y = S, Se) under metal-free conditions

Thiol (selenol) esters were synthesized by a direct oxidative coupling reaction of aldehydes with disulfides (diselenides) under metal-free conditions.

Metal-free sp3C–H functionalization: a novel approach for the syntheses of selenide ethers and thioesters from methyl arenes

A DTBP-promoted, operationally simple, metal-free and solvent-free formation of C–Se and C–S bonds through sp³C–H functionalization of methyl arenes with diselenides and disulfides is described.

Selective approach to thioesters and thioethers via sp3 C–H activation of methylarenes

Novel CDC approaches for the synthesis of thioesters and thioethers was developed via sp³ C–H activation of methylarenes and subsequent functionalization.

Efficient Synthesis of Thioesters and Amides from Aldehydes by Using an Intermolecular Radical Reaction in Water

The combination of the water-soluble radical initiator, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044) and the surfactant, cetyltrimethyl-ammonium bromide (CTAB), was found to be the most suitable condition for the effective and direct synthesis of useful active thioesters (pentafluorophenyl thioesters) in water. In addition, the direct amidation of aldehydes was achieved by the addition of the amines to the thioesterification reaction mixture in water.