Organic Syntheses, CV 8, 546
Submitted by Lal C. Vishwakarma, Orum D. Stringer, and Franklin A. Davis
1.
Checked by James Pribish and Edwin Vedejs.
1. Procedure
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).
2. Notes
1. A Teflon-coated, heavy duty, oval-shaped spin bar was used by the submitters for efficient stirring.
2. A Dean–Stark water separator equipped with a Teflon stopcock for water removal was used.
3. Linde powdered 5-Å molecular sieves were used as obtained from the supplier.
4. Amberlyst 15 ion-exchange resin is a strongly acidic, macroreticular resin purchased from Aldrich Chemical Company, Inc. The reaction fails in the absence of the acid catalysts.
7. A more convenient oxidation method has since been developed.
2
8.
Analytical reagent-grade chloroform, Fisher Scientific Company, was used as obtained.
12. Careful recrystallization from
ethyl acetate (saturated solution at 25°C; cool to −20°C) gave colorless crystals, ca. 20% recovery, mp
95–95.5°C.
13. Exothermic decomposition of a 500-g quantity after 2 weeks of storage at room temperature is reported by Dr. G. C. Crockett of Aldrich Chemical Company, Inc. Sufficient force was generated to shatter the container and char the
oxaziridine.
3. Discussion
This procedure is representative of a general procedure for the synthesis of
trans-2-sulfonyloxaziridines previously reported on a small scale (Table I).
3 trans-2-(Phenylsulfonyl)-3-(p-nitrophenyl)oxaziridine was prepared on a 0.16-molar scale in greater than
85% yield. The Baeyer–Villiger-type oxidation of the sulfonimine affords only the
trans-oxaziridine. The synthesis of the sulfonimine (PhSO
2N=CHPh) directly from the sulfonamide and aromatic aldehyde is described here. This modification avoids use of the intermediate
diethyl acetal used in earlier preparations of these compounds.
3;
4
2-Sulfonyloxaziridines are useful aprotic and neutral oxidizing reagents that, in general, afford greater selectivity for oxidations than do peracids.
2-Sulfonyloxaziridines have been employed in the oxidation of sulfides to sulfoxides,
5 disulfides to thiosulfinates,
5 selenides to selenoxides,
6 thiols to sulfenic acids (RSOH),
7 organometallic reagents to alcohols and phenols,
8 ketone and ester enolates to α-hydroxy carbonyl compounds,
9 in the epoxidation of alkenes,
10 and in the conversion of chiral amide enolates to optically active α-hydroxy carboxylic acids (93–99% ee).
11,12 These reagents can be used in the study of reactive oxidation intermediates and for mechanistic studies of oxygen-transfer reactions because of the ease with which the course of the oxidation can be monitored by proton NMR.
TABLE I
PREPARATION OF 2-SULFONYLOXAZIRIDINES3a,b
|
|
Yield (%) |
mp (°C, dec) |
|
R = Ph, Ar = 3-NO2Ph |
83 |
113–115 |
R = Ph, Ar = 4-NO2Ph |
80 |
134–136 |
R = Me, Ar = Ph |
85 |
59–61 |
R = PhCH2, Ar = Ph |
90 |
118–119 |
|
Oxidation of chiral sulfonimines (R
*SO
2N=CHAr)
13 and chiral sulfamylimines (R
*RNSO
2N=CHAr)
14 affords optically active
2-sulfonyloxaziridines and
2-sulfamyloxaziridines, respectively. These chiral, oxidizing reagents have been used in the asymmetric oxidation of sulfides to sulfoxides (15–68% ee),
13,14,15 selenides to selenoxides (8–9% ee),
16 enolates to α-hydroxycarbonyl compounds (8–37% ee),
17 and in the asymmetric epoxidation of alkenes (15–40% ee).
18 The synthetic applications of these reagents has been reviewed.
19
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