Trimethylsulphonium iodide

The reaction of trimethylsulphonium iodide [32], or polymer-supported sulpho-nium salts [33], with aldehydes and ketones produces oxiranes under relatively mild... 

Phase-transfer catalytic conditions provide an extremely powerful alternative to the use of alkali metal hydrides for the synthesis of cyclopropanes via the reaction of dimethyloxosulphonium methylides with electron-deficient alkenes [e.g. 54-56] reaction rates are increased ca. 20-fold, while retaining high yields (86-95%). Dimethylphenacylsulphonium bromide reacts in an analogous manner with vinyl-sulphones [57] and with chalcones [58] and trimethylsulphonium iodide reacts with Schiff bases and hydrazones producing aziridines [59]. 

Dialkyl sulphides are converted into trialkylsulphonium salts by treatment with an alkyl halide (the bromide or iodide is usually the reactant of choice). An important example of this group is trimethylsulphonium iodide, which is used as a methylene transfer reagent by virtue of its being converted in the presence of base into a sulphur ylide, which is a nucleophilic carbene equivalent. 

Benzylideneaniline (18.1 g, 0.1 mol) and tetrabutylammonium hydrogen sulphate (0.5 g, 1.35 mol) are dissolved in dichloromethane (100 ml) and a layer of 50 per cent aqueous sodium hydroxide introduced under this solution. Trimethylsulphonium iodide (20.4 g, 0.1 mol) is then added and the whole warmed at 50 °C with vigorous stirring for 2 hours, whereupon the originally undissolved sulphonium salt disappears. The mixture is poured on to ice, the organic phase separated, washed with water and dried. The solvent is evaporated and the residue distilled under reduced pressure to afford 1,2-diphenylaziridine (94%), b.p. 120°C/0.05mmHg. 

Dissolve 5.3 g (0.05 mol) of benzaldehyde (previously shaken with sodium hydrogen carbonate solution) and 0.25 g (0.67 mmol) of tetrabutylammonium iodide in 50 ml of dichloromethane. Place this solution in a 250-ml, three-necked round-bottomed flask equipped with an efficient sealed stirrer unit, a reflux condenser and a thermometer sited in a screw-capped adapter, and supported in an oil bath mounted on an electric hot plate. Introduce 50 ml of a 50 per cent (w/v) aqueous solution of sodium hydroxide, and then 10.2 g (0.05 mol) of finely powdered trimethylsulphonium iodide. Adjust the electric hot plate so that the oil bath is maintained at a constant temperature of 55 °C for 60 hours and during this period stir the reaction mixture rapidly (1). Pour the reaction mixture on to ice, separate the organic phase and extract the aqueous solution with one 20 ml portion of dichloromethane. Wash the combined organic phases successively with four 20 ml portions of water, two 10 ml portions of a saturated solution of sodium metabisulphite and finally two 20 ml portions of water. Dry the organic phase over anhydrous calcium sulphate, remove the dichloromethane on a rotary evaporator and distil the residue. Collect the phenyloxirane as a fraction having b.p. 191— 192 °C the yield is 4.7 g (78%). 

Alkyl-l-aryloxiranes are obtained by heating a mixture of trimethylsulphonium iodide, f-BuOK, and an alkyl aryl ketone in the absence of a solvent. Semistabilized allyUc telluro-nium or arsonium ylides are obtained by treating their precursor salts with f-BuOK as well as other bases in Additions... 

The reaction of chalcones and trimethylsulphonium iodide and KOH in the solid state gave the corresponding cyclopropanes (Scheme 42). 

The most satisfactory results so far in this area are to be found in a report of the reaction of benzaldehyde with trimethylsulphonium iodide and aqueous base according to equation (10), where, under optimum conditions and catalysed by (23 R = C2H5), up to 97% enantiomer excess in the oxirane product can be achieved. Possible rationalizations have been discussed for these processes, and the role of the )S-hydroxyethyl substituent at the quaternary centre seems to be significant in both catalytic efficiency and enantioselectivity. Further advances in this field can be expected. 

Ylides of Sulphur, Selenium, Tellurium, and Related Structures 341 halide ion present and the NaOH concentration." Under phase-transfer-catalysed conditions, involving methylene chloride and water solvents, sodium hydroxide as the base, and tetrabutylammonium iodide as a transfer agent, trimethylsulphonium iodide and benzaldehyde afforded a 90% yield of styrene oxide." An equally good yield was obtained with cinnamal-dehyde, but low yields were obtained with acetophenone and benzo-phenone. 

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