A. N-Benzylidenebenzenesulfonamide. A 3-L, one-necked, round-bottomed flask is equipped with a mechanical stirrer (Note 1), Dean–Stark water separator (Note 2), a double-walled condenser attached to an argon gas inlet, and outlet needle connectors through a mineral oil bubbler. Into the flask are placed 150 g of Linde 5A powdered molecular sieves (Note 3), 2.0 g of Amberlyst 15 ion-exchange resin (Note 4), 157 g of benzenesulfonamide (Note 5), 1650 mL of dry toluene, and 107.5 g (1.014 mol) of freshly distilled benzaldehyde (Note 5). The reaction mixture is stirred and heated at reflux under an argon atmosphere. Water that separates during the reaction is periodically removed and refluxing is continued until water separation ceases (ca. 16 hr). The reaction mixture is cooled to room temperature without stirring and the insoluble materials are filtered through a 500-mL-capacity sintered-glass funnel of medium porosity. The residue in the filter funnel is washed thoroughly with another 700 mL of toluene in three portions. The collected filtrate is concentrated with a rotary evaporator to give a thick, yellow, oily residue that usually solidifies on standing. The residue is triturated with 800 mL of distilled pentane and the solid is broken into a powder with the aid of a flat-ended glass rod. The solid is separated by filtration through a 500-mL sintered-glass funnel of medium porosity, washed with distilled pentane (2 × 100 mL), and air-dried. The yield is 212 g (87%); mp 76–80°C (Note 6).

Although of sufficient purity for the next step, the sulfonimine can be further purified by recrystallization. In a 2-L Erlenmeyer flask containing 150 mL of ethyl acetate is dissolved, with warming, 212 g of the crude sulfonimine. After the mixture is cooled to room temperature, about 400 mL of pentane is added and the solution is allowed to stand at room temperature for 2–3 hr. The colorless crystalline product is collected by filtration, washed with 100 mL of pentane, and air-dried to give 191.5 g (78%), mp 78–80°C. The washings and filtrate are combined and the volume reduced by about one-third using a rotary evaporator. A second crop of crystals, 20.2 g (8%), mp 75–79°C, was obtained on standing for several hours.

B. (±)-trans-2-(Phenylsulfonyl)-3-phenyloxaziridine. (See (Note 7).) A 5-L, three-necked flask is equipped with a mechanical stirrer and a 500-mL pressure-equalizing addition funnel. Into the flask are placed 500 mL of saturated aqueous sodium bicarbonate solution, 12.5 g (0.055 mol) of benzyltriethylammonium chloride (BTEAC), and 122.5 g (0.50 mol) of N-benzylidenebenzenesulfonamide dissolved in 380 mL of chloroform (Note 8). The reaction mixture is stirred vigorously at 0–5°C in an ice bath while a solution of 111.6 g (0.55 mol) of 85% m-chloroperoxybenzoic acid (MCPBA) dissolved in 1000 mL of chloroform is added dropwise. After the addition of the peracid, which takes about 1 hr, the reaction mixture is stirred for an additional hour at this temperature. A 3-L separatory funnel is used to separate the chloroform solution and wash it successively with 600 mL of cold water, 600 mL of aqueous 10% sodium sulfite, water (2 × 600 mL) and 250 mL of a saturated sodium chloride solution (Note 9). After the chloroform solution is dried over anhydrous potassium carbonate for 2 hr (Note 10), it is filtered and solvent is removed with a rotary evaporator, keeping the water-bath temperature below 40°C. The resulting white solid residue is washed with a small portion of pentane, dissolved in a minimum of ethyl acetate (about 700–800 mL) without heating, and filtered through fluted filter paper; 400 mL of pentane is added to the filtrate. After the white crystalline oxaziridine is cooled in the refrigerator overnight, it is separated by filtration, transferred to a 500-mL Erlenmeyer flask, washed with 200 mL of pentane, filtered, and air-dried for 1 hr. The yield is 83.5 g; mp 92–94°C. The mother liquor is reduced to about 300 mL and cooled in the refrigerator to give 36.6 g of a light-yellow solid; mp 87–90°C. This second crop is placed in a 250-mL Erlenmeyer flask and triturated with 50 mL of anhydrous ether followed by the addition of 60 mL of pentane. The oxaziridine is isolated by filtration to give 31.1 g; mp 94–95°C (dec) (Note 11) and (Note 12). The combined yield is 114.6 g (88%).

The 2-sulfonyloxaziridine can be stored in a brown bottle in the refrigerator. Storage at room temperature is potentially hazardous (Note 13).