Checked by Wayne Schnatter and Martin F. Semmelhack.
1. Procedure
A.
Phenyl vinyl sulfide. In a
1-L, three-necked, round-bottomed flask fitted with magnetic stirrer, condenser, addition funnel, and nitrogen-inlet tube is placed
400 mL of ethanol.
Sodium metal (23 g, 1 g-atom), cut into small pieces, is added with stirring. When conversion to
sodium ethoxide is complete (5–15 min), the stopper of the addition funnel is removed under a positive flow of
nitrogen, and
benzenethiol (110 g, 1 mol) is poured into the addition funnel. The stopper is put in place, and the
benzenethiol is added over 15–20 min to the cloudy, gray
sodium ethoxide solution. The reaction mixture warms spontaneously and becomes clear brown. At 25°C this solution is transferred by
stainless-steel cannula (Note
1) over 45 min to a stirred solution of
1,2-dibromoethane (272 g, 1.45 mol) in ethanol (28 mL) contained in a
2-L, three-necked round-bottomed flask equipped with a
mechanical stirrer, addition funnel,
reflux condenser, nitrogen-inlet tube, and
internal thermometer (Note
2). The reaction temperature is maintained at 25–30°C by cooling with an
ice bath. The mixture is stirred under
nitrogen for 30 min and treated for an additional 30 min with ethanolic
sodium ethoxide prepared from
40 g (2.17 g-atom) of sodium and 800 mL of ethanol (Note
3). The resulting mixture is stirred at reflux for 8 hr (Note
4), cooled, and treated with
750 mL of benzene and 750 mL of water. The organic layer is separated, washed with water (2 × 50 mL) and
brine (100 mL), and concentrated by rotary evaporation. The yellow oil that results is distilled to give
70–87 g (
50–65%) of
phenyl vinyl sulfide, bp
91–93°C/20 mm (Note
5) and (Note
6).
B.
Phenyl vinyl sulfone. In a
250-mL, three-necked, round-bottomed flask fitted with a magnetic stirrer, condenser, addition funnel, and thermometer is placed
19.7 g(0.145 mol) of phenyl vinyl sulfide dissolved in
70 mL of glacial acetic acid.
Hydrogen peroxide (30%, 56 mL, 0.5 mol) is added slowly at such a rate to maintain a reaction temperature of 70°C (Note
7). The reaction mixture is heated at reflux for 20 min, cooled, and treated with
ether (150 mL) and water (200 mL). The organic phase is separated, washed with water (50 mL) and
brine (50 mL), and concentrated at 70°C/0.3 mm for 3 hr to afford
18–19 g (
74–78%) of
phenyl vinyl sulfone as a colorless solid, mp
64–65°C. Although this material is sufficiently pure for most purposes, recrystallization from
hexane affords colorless crystals, mp
66–67°C (Note
8).
C.
Phenyl vinyl sulfoxide. A
500 mL, three-necked, round-bottomed flask equipped with a dropping funnel and magnetic stirrer is charged with
20 g (0.147 mol) of phenyl vinyl sulfide and
250 mL of dichloromethane. The solution is stirred and cooled to −78°C while a solution of
m-chloroperbenzoic acid (25.4 g, 1.0 equiv) in 200 mL of dichloromethane is added dropwise during a 30-min period. The mixture is stirred and warmed to room temperature for 1 hr in a
water bath at 30°C. The mixture is then poured into
300 mL of saturated sodium bicarbonate solution, and the mixture is extracted with three
250-mL portions of dichloromethane. The combined organic extracts are washed with three 250-mL portions of water and dried over anhydrous
magnesium sulfate. The solvent is removed by rotary evaporation and the residual liquid is distilled to afford
15–16 g (
68–70%) of
phenyl vinyl sulfoxide as a colorless liquid, bp
98°C/0.6 mm (Note
9) and (Note
10).
2. Notes
1. The cannula is a
stainless-steel tube, 16-gauge, sharpened to a needle at both ends, and 60 cm long. One end is placed through a
rubber septum into the flask containing the
1,2-dibromoethane solution, while the other end is positioned under the surface of the
benzenethiolate solution. Control of the
nitrogen pressure allows slow transfer of the
benzenethiolate solution.
2. The yield in the previously published method for the preparation of this sulfide is low, affording chiefly
1,2-bis(phenylthio)ethane.
2 The problem is overcome here by utilization of an inverse addition procedure.
3. Alternatively, dry powered
sodium ethoxide may be substituted with a corresponding reduction of the reaction volume.
5. This product has the following spectral properties: IR (neat) cm
−1: 3040, 1585, 1475, 1435, 1085, 1020, 950, 735, and 680;
1H NMR (chloroform-
d) δ: 5.25 (superimposed doublets, 2 H,
J = 12 and 18, terminal vinyl), 6.50 (dd, 1 H,
J = 12 and 18, olefinic,), 7.32 (m, 5 H, aromatic).
6. When stored at room temperature,
phenyl vinyl sulfide becomes yellow-colored within 1 day and a black syrup after 1 week. This decomposition can be substantially retarded by storage under a
nitrogen or
argon atmosphere in a freezer.
7. The submitter observed the temperature increase to 70°C during addition of the first
10 mL of hydrogen peroxide. The checkers noted that the mixture never rose in temperature to 70°C.
8. This product has the following spectral properties: IR (CHCl
3) cm
−1: 3020, 1445, 1380, 1315, 1145, 1080, and 965;
1H NMR (chloroform-
d) δ: 5.96 (d, 1 H,
J = 10, olefinic), 6.33 (d, 1 H,
J = 17, olefinic), 6.75 (dd, 1 H,
J = 10 and 17, olefinic), 7.55 (m, 3 H, aromatic), 7.85 (m, 2 H, aromatic).
9. Earlier citations
3 report bp
105–110°C (1.5 mm) and
93–95°C (0.2 mm).
10. This product has the following spectral properties: IR (neat) cm
−1: 3025, 1720, 1680, 1480, 1440, 1045, 750, and 690;
1H NMR (chloroform-
d) δ: 5.63–6.17 (m, 2 H, olefinic H), 6.44–6.87 (m, 1 H, olefinic H), 7.10–7.55 (m, 5 H, aromatic H).
3. Discussion
The procedure for oxidation of the sulfide to the sulfone is based on that reported earlier by Bordwell and Pitt.
4 The synthetic utility of
phenyl vinyl sulfone and sulfoxide derives not only from their ability to serve as excellent Michael acceptors toward such reagents as enolate anions and organometallics
5,6,7,8,9,10,11,12 but also as moderately reactive dienophiles in Diels–Alder reactions.
13,14,15,16 The resulting adducts, in turn, can be chemically modified so that these electron-deficient olefins serve as useful synthons for
acetylene,
13 ethylene,
14 terminal olefins,
15 vinylsilanes,
17 and
ketene18 in [4 + 2] cycloadditions.
Phenyl vinyl sulfone undergoes ready cycloaddition to Danishefsky's diene in the first step of a protocol for the regiospecific γ-alkylation of
2-cyclohexenones.
19 Furthermore, the ready lithiation of phenyl vinyl sulfones
20 and sulfoxides
21 represents a convenient route to α-(phenylsulfonyl) and α-(phenylsulfinyl)vinyllithium reagents.
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