Organoselenium and Organotellurium Oxidation and Reduction

Abstract

Oxygenated and reduced selenium and tellurium compounds, particularly thoese of practical importance have been extensively investigated especially during the last few decades. Selenium(IV) oxide, selenoxides, selenones, seleninic and peroxyseleninic acids, selenenamides and seleninamides are involved in oxyfunctionalization of unsaturated hydrocarbons, their derivatives, alkylarenes, sulfides and amines, carbon‐oxygen and carbon‐carbon bond cleavage, ring closure and ring transformations, syn ‐elimination, sigmatropic [2,3]‐rearrangement and other, chemo‐ regio‐ and stereocontrolled reactions. The chemistry of oxygenated tellurium compounds has been less extensively explored than their selenium counterparts;, nevertheless some of them have been successfully used for oxyfunctionalization of different groups of organic compounds while telluroxide elimination has gained more attention in the last years becoming a well‐established method for the synthesis of olefins. Hydrogen selenide and telluride, alkali selenides and tellurides, selenoles and telluroles are the most common reduced derivative of these elements. Their properties are expressed in many reactions such as reduction and deoxygenation of different groups of organic compounds alkenes, alkynes, ethers, carbonyl compounds, esters, lactones, oxiranes, nitrogen, sulfur and halogen compounds, as well as dealkylation of tertiary amines. The method for preparation of the different oxygenated and reduced selenium and tellurium compounds are described, their reactions are reviewed, their usefulness in synthesis is indicated and more representative mechanisms are discussed.

An Easy Synthetic Approach to Construct Some Ebselen Analogues and Benzo[b]selenophene Derivatives: Their Antioxidant and Cytotoxic Assessment

“…Synthesis of organoselenium compounds of different classes continues to be a very active research area, because of their distinct chemical and biological properties . In fact, a variety of organoselenium compounds are well known for their antimicrobial, anti‐inflammatory, antioxidant, and biocidal activities . Their practical application in medicine for the treatment of tumors and cancers is a subject of current intense interest .…”

Optically Active Selenoxides: Structural and Synthetic Aspects

“…The reaction of the hydroxyselenoxide 40 with strong organic acids (3,5-dinitrobenzoic, p-toluenesulfonic or trifluoromethanesulfonic )in the presence of MgSO 4 gave the corresponding selenuranes 44-47, respectively (Scheme 6) [36,37]. It is well known that allyl selenoxides undergo very fast [2,3] sigmatropic rearrangement, producing allylic alcohols (Scheme 7), while vinyl selenoxides are able to eliminate selenic acid, which leads to the cumulene system (Scheme 8). The asymmetric version of both methods can be used to synthesize optically active alcohols or allenes, respectively [38][39][40][41].…”

“…The first example of this methodology, which was used in the preparation of optically active allylic alcohol, was reported in 1991 [42] and was based on the in situ generation of the optically active, diastereoisomerically enriched, geranyl [2.2]paracyclophanyl selenideoxide 49 by treatment of the corresponding optically active geranyl selenide 48 with meta-chloroperbenzoic acid (MCPBA). This protocol gave linalool 51 with 67% enantiomeric excess (ee) via selenenic ester 50 which was formed as a result of the [2,3]sigmatropic rearrangement of selenoxide 49 (Scheme 9).…”

“…The first example of this methodology, which was used in the preparation of optically active allylic alcohol, was reported in 1991 [42] and was based on the in situ generation of the optically active, diastereoisomerically enriched, geranyl [2.2]paracyclophanyl selenideoxide 49 by treatment of the corresponding optically active geranyl selenide 48 with meta-chloroperbenzoic acid (MCPBA). This protocol gave linalool 51 with 67% enantiomeric excess (ee) via selenenic ester 50 which was formed as a result of the [2,3] A similar oxidation of geranyl selenide 52 bearing a chiral ferrocenyl group afforded the corresponding diasteromeric selenoxides 53, which upon the [2,3]sigmatropic rearrangement gave optically active linalool 51 in moderate yields and an improved ee (83%) (Scheme 10) [43]. This approach was also applied in the synthesis of a series of cinnamyl selenides 55-57 bearing other chiral groups.…”

“…It should be noted here that both acids can exist as chiral tetravalent (5a or 6a) or achiral divalent (5b [7][8][9] or 6b [10][11][12]) tautomers. The highly polarized heteroatom-oxygen bond is responsible for the interesting oxidative properties of sulfoxides [1] and selenoxides [2], and their ability to: a) generate the α-carbanions 3 [3] or 4 [4] for compounds containing the acidic α-methylene hydrogen atoms 1a or 2a (Scheme 1); b) undergo an internal type elimination of the E2 type for compounds containing β-hydrogen atoms, which leads to the formation of the corresponding, generally very unstable, seleninic 5 or sulfenic 6 acids and unsaturated carbon derivatives 7 (Scheme 1) [5,6]. It should be noted here that both acids can exist as chiral tetravalent (5a or 6a) or achiral divalent (5b [7][8][9] or 6b [10][11][12]) tautomers.…”