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A Focus on Vinyl Selenones molecules Review ReviewModern Synthetic Strategies with Organoselenium Reagents: Modern Synthetic Strategies with Organoselenium Reagents: AA FocusFocus onon VinylVinyl SelenonesSelenones Martina Palomba, Italo Franco Coelho Dias, Ornelio Rosati and Francesca Marini * Martina Palomba, Italo Franco Coelho Dias, Ornelio Rosati and Francesca Marini * Department of Pharmaceutical Sciences (Group of Catalysis, Synthesis and Organic Green Chemistry), UniversityGroup of Catalysis, of Perugia, Synthesis Via del andLiceo, Organic 06123 GreenPerugia, Chemistry, Italy; [email protected] Department of Pharmaceutical (M.P.); Sciences, italo.francocoelhodias@studeUniversity of Perugia, Via delnti.unipg.it Liceo, 06123 (I.F.C.D.); Perugia, [email protected] Italy; [email protected] (O.R.) (M.P.); *[email protected] Correspondence: [email protected] (I.F.C.D.); [email protected] (O.R.) * Correspondence: [email protected] Abstract: In recent years, vinyl selenones were rediscovered as useful building blocks for new syn- Abstract: In recent years, vinyl selenones were rediscovered as useful building blocks for new thetic transformations. This review will highlight these advances in the field of multiple-bond-form- synthetic transformations. This review will highlight these advances in the field of multiple-bond- ing reactions, one-pot synthesis of carbo- and heterocycles, enantioselective construction of densely forming reactions, one-pot synthesis of carbo- and heterocycles, enantioselective construction of functionalized molecules, and total synthesis of natural products. densely functionalized molecules, and total synthesis of natural products. Keywords: selenium; domino reactions; heterocycles; natural products; spiro compounds; annula- Keywords: selenium; domino reactions; heterocycles; natural products; spiro compounds; annula- tions; enantioselective synthesis; organocatalysis tions; enantioselective synthesis; organocatalysis Citation: Palomba, M.; Dias, I.F.C.; Rosati, O.; Marini, F. Modern Syn- thetic Strategies with Orga- noselenium Reagents: A Focus on 1. Introduction 1. Introduction Vinyl Selenones. Molecules 2021, 26, Selenium chemistry has rapidly grown over the past years and nowadays selenium Selenium chemistry has rapidly grown over the past years and nowadays sele- x. https://doi.org/10.3390/xxxxx reagents are recognized tools in the chemo-, regio-, and stereoselective synthesis of mol- Citation: Palomba, M.; Franco nium reagents are recognized tools in the chemo-, regio-, and stereoselective synthesis of ecules containing selenium or not [1–3]. In fact, selenium functionalities can be easily re- Coelho Dias, I.; Rosati, O.; Marini, F. molecules containing selenium or not [1–3]. In fact, selenium functionalities can be easily Academic Editors: Luana Bagnoli duced, eliminated or transformed into other functional groups with high stereocontrol. In Modern Synthetic Strategies with reduced, eliminated or transformed into other functional groups with high stereocontrol. and Vladimir A. Potapov Organoselenium Reagents: A Focus Inthis this field, field, over over the the past past decade, decade, the the chemistry chemistry of of vinyl vinyl selenones selenones has has been been the the object of on Vinyl Selenones. Molecules 2021, renewed interest, leading to the development of diverse and powerful methods with ap- Received: 30 April 2021 renewed interest, leading to the development of diverse and powerful methods with appli- 26, 3148. https://doi.org/10.3390/ plications in challenging fields of organic synthesis, such as the enantioselective synthesis Accepted: 21 May 2021 cations in challenging fields of organic synthesis, such as the enantioselective synthesis and molecules26113148 and the total synthesis of natural products. The chemistry of these hexavalent, tetra-coor- Published: 25 May 2021 the total synthesis of natural products. The chemistry of these hexavalent, tetra-coordinated seleniumdinated selenium compounds compounds shows interestingshows interesting analogies analogies with that with of that the correspondingof the corresponding vinyl Academic Editors: Luana Bagnoli vinyl sulfones. Both contain an electron-withdrawing group that stabilizes vicinal carban- Publisher’s Note: MDPI stays neu- sulfones. Both contain an electron-withdrawing group that stabilizes vicinal carbanions and Vladimir A. Potapov tral with regard to jurisdictional andions activatesand activates the double the double bond bond to conjugate to conjugate nucleophilic nucleophilic attack, attack, but the but weak the weak C-Se bondC-Se claims in published maps and insti- donatesbond donates to the to phenylselenonyl the phenylselenonyl moiety, moiety, a better a better leaving leaving group group character character for further for further sub- Received: 30 April 2021 tutional affiliations. stitutionsubstitution or elimination or elimination reactions. reactions. In thisIn this review, review, recent recent applications applications of vinylof vinyl selenones selenones in Accepted: 21 May 2021 in domino or sequential one-pot processes for the assembly of carbo- and heterocycles, Published: 25 May 2021 domino or sequential one-pot processes for the assembly of carbo- and heterocycles, the functionalizationthe functionalization of biomolecules, of biomolecules, and and the th organocatalyzede organocatalyzed enantioselective enantioselective construction construc- oftion all-carbon of all-carbon quaternary quaternary stereocenters stereocenters will bewill presented be presented and discussed and discussed (Figure (Figure1). Main 1). Publisher’s Note: MDPI stays neutral Copyright: © 2020 by the authors. Main advantages of such multiple-bond forming strategies are the mild and operationally with regard to jurisdictional claims in advantages of such multiple-bond forming strategies are the mild and operationally simple Submitted for possible open access simple reaction conditions, the good to excellent yields, and the high chemo-, regio-, and published maps and institutional affil- reaction conditions, the good to excellent yields, and the high chemo-, regio-, and stereo- publication under the terms and iations. selectivities.stereo-selectivities. Examples Examples of use ofof vinyluse of selenones vinyl selenones in the total in the synthesis total synthesis of natural of products natural conditions of the Creative Commons willproducts also bewill shown. also be shown. Attribution (CC BY) license (http://creativecommons.org/licenses /by/4.0/). SeO 2Ph Carbo- and heterocycles synthesis Functionalization Copyright: © 2021 by the authors. R1 R2 via Michael initiated ring closure reactions of carbohydrates and nucleotides Licensee MDPI, Basel, Switzerland. This article is an open access article Asymmetric Total syn thesis of distributed under the terms and organocatalysis natural products conditions of the Creative Commons Attribution (CC BY) license (https:// Figure 1. Vinyl selenones as versatile reagentsreagents in organic synthesis. creativecommons.org/licenses/by/ 4.0/). Molecules 2021, 26, x. https://doi.org/10.3390/xxxxx www.mdpi.com/journal/molecules Molecules 2021, 26, 3148. https://doi.org/10.3390/molecules26113148 https://www.mdpi.com/journal/molecules Molecules 2021, 26, 3148 2 of 25 2. Synthesis of Vinyl Selenones and Their Biological Activities Selenones are usually prepared by oxidation of the corresponding selenides [4,5]. The first oxidation of selenides to selenoxides is fast, but the decreased electron density on the selenium atom makes selenoxides less prone to the second oxygen transfer. Even if, several strong oxidants convert selenides into selenones, i.e., KMnO4 [6], peroxyacids or their salts [6,7], H2O2 in the presence of benzenseleninic acid [8], HMPA peroxo complex ® of molybdenum [9], Oxone [10], and HOF·CH3CN complex [11], 3-chloroperoxybenzoic acid (m-CPBA) [12] is the reagent of choice for the oxidation of vinyl selenides (Scheme1, route a). It is used in excess in alcoholic, ethereal or halogenated solvents. Recently, the greener Oxone® was used to generate vinyl selenones [13] in water without addition of any catalyst or co-solvent. Scheme 1 . Synthetic approaches toScheme vinyl selenones. 1. Synthetic approaches to vinyl selenones. In recent years, selenium-containing compounds have showed interesting biological activities and a great potential in medicinal chemistry, particularly in cancer therapy [14]. Bioactive vinyl selenones were recently prepared through the multistep sequence described in Scheme1, route b. In this protocol the Wittig–Horner reaction between phenylse- leninylmethyl phosphonates and variously substituted aromatic aldehydes generated vinyl selenoxides which were transformed into the corresponding selenone by oxidation with m-CPBA [15]. These compounds were evaluated for their in vitro and in vivo anticancer activities. They showed tubulin polymerization inhibition and antiproliferative activity against several cancer cell lines. The structure of the most active compound is reported in Figure2 together with other diaryl or aryl alkylselenones with antiproliferative [ 16] or pesticide activities. [17,18]. Scheme 2 . Cyclopropanations of active methylene compounds with vinyl selenones. Molecules 2021, 26, x FOR PEER REVIEW 3 of 26 Molecules 2021, 26, 3148 3 of 25 Figure 2. Biologically active selenones. 3. Michael-Initiated Ring Closures Michael initiated ring closure reactions ofof vinyl selenones demonstrated toto bebe highly efficientefficient
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