Johnathan V. Matlock, V. Aggarwal, E. McGarrigle
Mar 31, 2016
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Abstract
(2-Bromoethyl)diphenylsulfonium Trifluoromethanesulfonate [247129-85-7] C15H14BrF3O3S2 (MW 443.30) InChI = 1S/C14H14BrS.CHF3O3S/c15-11-12-16(13-7-3-1-4-8-13)14-9-5-2-6-10-14;2-1(3,4)8(5,6)7/h1-10H,11-12H2;(H,5,6,7)/q+1;/p-1 InChIKey = SAXNFOVPRAUGNK-UHFFFAOYSA-M (used as a solid precursor for in situ generation of diphenylvinylsulfonium triflate1 [247129-88-0] an annulation reagent for the synthesis of heterocycles via epoxidation, aziridination, cyclopropanation, and proton-transfer reactions) Alternate Name: bromoethyldiphenylsulfonium triflate. Physical Data: mp 86–87 °C (toluene/Et2O). Solubility: typically insoluble in petrol-derived solvents (e.g., petroleum ether, n-pentane, and n-hexanes) and non-polar ethereal solvents (e.g., diethyl ether). Partially soluble in THF:H2O (2:1). Soluble in Acetone, CHCl3, CH2Cl2, CH3CN, DMSO, DMF, EtOH, MeOH, and THF. Form Supplied in: grey to tan amorphous solid available from several chemical suppliers or synthesized in two steps from 2-bromoethanol.2-4 Preparative Methods: bromoethyldiphenylsulfonium triflate is synthesized in two steps starting from commercially available 2-bromoethanol. Treatment of 2-bromoethanol with triflic anhydride in pyridine/CH2Cl2 generates the corresponding 2-bromoethyl triflate (eq 1). Without purification, 2-bromoethyl triflate is then reacted directly with diphenyl sulfide in refluxing toluene to generate bromoethyldiphenylsulfonium triflate, which is then isolated by precipitation from diethyl ether (eq 2).2-4 This chemistry is sufficiently robust to be conducted on scale in order to produce large quantities (up to 0.1 mol of 1 has been used in an annulation reaction) of the title compound.5 (1) (2) Purification: precipitation from diethyl ether: The crude sulfonium salt is dissolved in the minimum amount of CH2Cl2 and added dropwise to rapidly stirring diethyl ether leading to the precipitation of the title compound, which is then stirred for 20 min filtration of 1 as a grey amorphous solid before (R f 0.25 in 10% MeOH/CH2Cl2 on aluminum-backed silica gel plates). (Note: For further purification, stirring in Et2O overnight gave reduced yields, typically 5% lower than the reported yield. Precipitated material from the overnight procedure gave cleaner spectra by comparison [mp 86–87 °C] to the 20 min precipitation [mp 84–85 °C]). Bromoethyldiphenylsulfonium triflate isolated from either method is suitable for the chemistry described herein. Conversion to diphenylvinylsulfonium triflate and subsequent stability/lifetime of this reagent is directly related to the purity of the bromoethyldiphenylsulfonium triflate used. Single crystals suitable for X-ray were obtained by slow evaporation of a toluene solution.6 Handling, Storage, and Precautions: can be stored at room temperature without the need for inert atmospheres for >2 years without significant decomposition or loss of reactivity. To the best of our knowledge, its toxicity has not been studied; however, as it is a precursor to a potent alkylating agent, it should be manipulated with care (use of DMSO as a solvent should be avoided if possible, and special care should be taken to avoid contact with skin if use of DMSO is unavoidable). Skin/eye contact should be avoided.