N-Bromosuccinimide-Induced Dimethyl Sulfoxide Oxidation of Acetylenes

Abstract

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.

Bromination of silatranyl‐, germatranyl‐, silyl‐, and germyl‐phenylacetylenes

“…Analogous behavior was observed for 3,7,10-trimethyl-and 3-phenyl-substituted germatranes 2 and 9. It should be noted that we have not detected either diketoderivatives (R 3 GeC(O)C(O)Ph) or dibromo adducts (R 3 GeC(Br) C(Br)Ph) among the products of the reaction (14), whereas they are formed under the same conditions in the case of alkylphenylacetylenes [22].…”

“…Under an argon atmosphere [22], NBS (0.02 mol) was added in one portion with stirring to a solution of phenylacetylene (0.01 mol) in DMSO (30 ml). As a result, a transparent bright orange solution was obtained and in general noticeable amount of heat was produced.…”

Stereomutation of a 1,2,3-triketone: an example of an asymmetric reaction

“…The N-brornosuccinirnide (NBS)-promoted diniethyl sulfoxide (DMSO) oxidation of polyacetylenes (2,3) provides access to polyketones. until recently (4) a relatively little know11 class of compounds.…”

“…These workers reported geometry optimization of the planar rlmzs-rt.ot?s ( 2 ) and helical (5) conformations using CNDO/2 arid M I N D 0 2 IM. B. Rubin, personal conimunication SCF-MO computations, and found the helical conformation to be Inore stable by 21.8 kcal/mol.…”

Oxidation of benzoins to benzils in the presence of porphyrin sensitizers by air and sunlight or visible light

“…1,2-Diketones have been synthesized with different reagents, such as oxidation of 1,2-diols [37,38], oxidation of alkynes [39][40][41][42][43][44][45][46][47][48][49], oxidation of alkenes [50], oxidation of a-methylene ketones [51], rearrangement of a,b-epoxyketones [52][53][54], oxidation of vicinal dihaloalkenes [55], oxidation of epoxides [56], oxidation of 1,3-diols [57], and oxidation with molecular oxygen. They have been catalyzed by trichlorooxyvanadium [58], nickel-aluminum hydrotalcite [59], and chiral cobalt complex [60], while palladium-catalyzed oxidation of benzoins to benzils was achieved by using CsOH or K 2 CO 3 as a base [61][62][63].…”