The addition of less than 2 mol equiv. of N-bromosuccinimide (NBS) to a solution of diphenylacetylene in anhydrous dimethylsulfoxide (DMSO) leads to the formation of benzil in near-quantitative yield at room temperature. Under the same conditions stilbene gives the dibromo adduct. The conditions for this novel oxidation of an acetylene have been examined in some detail and it has been established that anhydrous DMSO must be employed as the solvent and that NBS is uniquely able to induce the oxidation. Preliminary studies indicate that alkyl aryl, dialkyl, and terminal acetylenes are converted to the corresponding a-dicarbonyl compounds, and that diphenylbutadiyne is oxidized to diphenyltetraketone. Optimum conditions for these latter oxidations have not yet been established. L'addition a la temperature ordinaire de N-bromosuccinimide (NBS), moins de 2 Cquivalents, a une solution de diphCnylacttylene dans du dimethylsulfoxyde (DMSO) conduit a la formation de benzil avec un rendement presque quantitatif. Dans les mimes conditions, le stilbene conduit au dCrivC dibromC. The combination of an N-haloamide or imide and an aqueous medium is often employed to convert an alcohol into a ketone or an olefin into a halohydrin (1). Hypohalous acid, formed in situ by hydrolysis -of the halogen source, is thought to be the oxidizing agent in most of these reactions (2). However, recent work by van Tamelen and Sharpless (3) and by Dalton and co-workers (4) indicates that the intervention of HOX is not obligatory. In aqueous glyme, N-bromosuccinimide (NBS) appears to effect direct transfer of positive bromine to a double bond (3); and, in the reaction of NBS with an olefin in moist dimethyl sulfoxide (DMSO), attack on the brominated cation or bromocarbonium ion is at least 95% by the DMSO (4). The bromohydrin is then produced by hydrolysis of the oxysulfonium intermediate 1.bromoketones are produced (5) and, with Nchlorosuccinimide or NBS in alcoholic solvents, the products are dichloro (6) or dibromoketals (7). In aqueous glyme, NBS effects direct transfer of bromine to a triple bond (7). This similar behavior of olefins and of acetylenes suggested that, in DMSO, a brominated vinyl cation might, like its dihydro analog, be trapped by the solvent to give 2, an unsaturated oxysulfonium cation. In the case of 2, however, competition may now occur between hydrolysis and either unimolecular (2 + 3 ; eq. 1) or bimolecular (2 + DMSO + 4; eq. 2) elimination of dimethyl sulfide. Loss of Br@ and dimethyl sulfide from 4, formed by the reactions of 2 or 3 with DMSO, would then lead, as indicated in eq. 3, to 5, an a-diketone, in what might be described as NBS-induced DMSO oxidation.Acetylenes resemble olefins in a number of respects in their behavior towards these halogenating agents. With hypobromous acid, di- For personal use only.
. Can. J. Chem. 54,2847Chem. 54, (1976. Ten acyclic and two cyclic 1,3-bissulfonium bistetrafluoroborates have been synthesized by appropriate modification of the literature procedures for the preparation of such compounds. The acyclic salts are deprotonated readily by one molar-equivalent of potassium hydroxide t o give 1,3-bissulfonium ylides. However, under the same conditions, the cyclic salts decompose. Hydrogen exchange experiments reveal that the C2 hydrogens of the cyclic salts are significantly less acidic than the C2 hydrogens of the acyclic salts. The relative acidities of the C?, hydrogens of the cyclic salts depend upon the medium and upon the configuration and conformation of the molecule, and preliminary attempts have been made to associate the kinetic and thermodynamic acidities of these hydrogens with their specific stereochemical environments.Deprotonation of a 1,3-bissulfonium salt is accompanied by a decrease of at least 5 kcal/mol in the barrier t o pyramidal inversion a t sulfur. However, attempts to establish the static and dynamic behaviour a t the carbanionic centre were not successful. SAUL WOLFE, PETER CHAMBERLAIN et TIMOTHY F. GARRARD. Can. J. Chem. 54,2847(1976. Dix dCrivCs bistitrafluoroborate de bissulfonium-1,3 acycliques et deux cycliques ont Ct C synthCtisCs par des modifications appropriks des procCdCs dCcrits dans la IittQature pour la preparation de tels composCs. Les sels acycliques sont dCprotonCs facilement par un equivalent molaire d'hydroxyde de potassium pour donner des ylures de bissulfonium-1,3. Cependant, sous les m&mes conditions, les sels cycliques se dkomposent. Des expkriences d'kchange d'hydrogtne rCvklent que les hydrogknes en C2 des sels cycliques sont passablement moins acide que les hydrogknes en C2 des sels acycliques. Les aciditCs relatives des hydroghnes en C2 des sels cycliques dCpendent du milieu et de la configuration et de la conformation de la molCcule. Des essais preliminaires ont Ct C faits pour associer les aciditis cinktiques et thermodynamiques de ces hydrogtnes avec leurs environnements stCrCochimiques spkifiques.La dCprotonation d'un sel de bissulfonium-1,3 est accompagnie d'un abaissement d'au moins 5 kcal/mol dans la barrkre d'inversion pyramidale B l'atome de soufre. Cependant, les essais pour Ctablir le comportement statique et dynamique au site carbanionique n'ont pas eu de succks.[Traduit par le journal]
Zehn acyclische und zwei cyclische Bis‐sulfoniumsalze der allgemeinen Struktur (A) wurden nach drei modifizierten Literaturmethoden dargestellt (Ausbeuten meist in g): Durch Alkylierung eines Sulfids wie (II) oder (VI) mit einem Alkylmercaptomethylhalogenid wie (I) in Gegenwart von AgBF4 zum Alkylrnercaptomethylsulfoniumsalz wie (III) bzw. (VII), dann weitere Alkylierung mit Trimethyl‐ (oder Triäthyl‐) ‐oxonium‐tetrafluoroborat zu (V) bzw. (VIII); analog wurden (IX) und (X) dargestellt (Methode a); Alkylierung mit Trimethyl(äthyhoxoniumtetrafluoroborat von Forrnaldehyddimethyl(diäthyl)dithioacetal zu (XI) und (XII) bzw. von 1,3‐Dithian zu (XIII) (Methode b); Reaktion des Sulfids (XIV) [aus Thiophenol, Paraformaldehyd und HCI‐Gas] mit Methyl(äthyl)mercaptan (XV) zum Dithiomethan (XVI) und dessen Alkylierung mit Trimethyl(äthyl)oxoniumtetrafluoroborat zu den Bis‐sulfoniumsalzen (XVII) bzw. (XVIII) (Methode c).
Tolan (Ia R′, R2: Phenyl) reagiert mit 2 Val N‐Brom‐succinimid in wasser:‐ freiem DMSO unter Bildung von Benzil (IIa R′, R2: Phenyl) (98% Ausbeute), während trans‐Stilben (III) mit den angegebenen Reagenzien nur das Dibromaddukt (IV) (meso‐Form) liefert.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.