Methyl (+/-)-2-phenylthiopropionate[1]
A solution of thiophenol (23.1 g, 0.21 moles) in THF (~ 100 ml) was added slowly to solution of methyl 2-bromopropionate 8 (39.0 g, 0.23 moles) and triethylamine (30.2 g, 0.30 moles) in THF (~ 200 ml) at 0degC. After 30 mins the mixture was filtered and the residue was washed with ethyl acetate (~ 300 ml). The filtrate was washed with 1N hydrochloric acid (~ 300 ml) and saturated sodium bicarbonate solution (3 x 300 ml). The aqueous phases were each extracted with ethyl acetate (300 ml). The combined organic phases were dried (MgSO4) and concentrated in vacuo to afford the thioether as a crude brown oil that was used without further purification.
delta(H) 1.46 (3H, d, J = 7.1 Hz, 3CH3); 3.65 (3H, s, COOCH3); 3.77 (1H, q, J = 7.1 Hz, 2CH); 7.22-7.48 (5H, m, Ph).
{Lit. values;[2] delta(H) 1.40 (d, J = 7 Hz); 3.55 (s); 3.60 (q, J = 7 Hz); 7.00-7.40 (m).}
vmax (liquid film); 3059; 2951; 1735; 1583; 1474; 1439; 1329; 1260; 1229; 1193; 1162; 1067; 1026; 749; 692 cm(-1).
{Lit. values; [3]v 3060; 1735; 1580; 1480; 1020; 740; 690 cm(-1).}
m/z (C.I., NH3); 214 (M + NH4+)
G.C. (50-240degC, 10degC min(-1)); RT = 12.0 mins.
Methyl (+/-)-alpha-phenylsulphinylpropionate[4]
A solution of methyl 2-phenylthiopropionate (crude, ~ 0.21 moles) in acetonitrile (200 ml) was added dropwise to a suspension of sodium periodate (49.4 g, 0.23 moles) in water (150 ml) at 0degC. The mixture was stirred at 20-25degC for 16 h. The mixture was filtered and concentrated in vacuo to remove the acetonitrile. The residue was extracted with dichloromethane (3 x 150 ml), dried (MgSO4) and concentrated in vacuo to afford the sulphoxide (45.9 g, ~100% from 8) as a yellow oil.
delta(H) (1:1 mixture of diastereoisomers) 1.28, 1.43 (total 3H, each d, J = 7.2 Hz, 3CH3); 3.47, 3.80 (total 1H, each q, J = 7.2 Hz, 2CH); 3.63, 3.64 (total 3H, each s, COOCH3); 7.45-7.62 (5H, m, Ph).
vmax (liquid film) 1735 (ketone); 1444; 1050 cm(-1).
m/z (C.I., NH3); 230 (M + NH4+)
T.L.C.; Rf ~ 0.20 (20% ethyl acetate, petrol).
Methyl alpha-phenylthioacrylate[5]
A solution of methyl alpha-phenylsulphinylpropionate (45.9 g, 0.22 moles), acetic anhydride (26.5 g, 0.26 moles) and methanesulphonic acid (2.7 g, 0.029 moles) in dichloromethane (400 ml) was left to stand for 16 h. The solvent and excess acetic anhydride were removed in vacuo and the crude product was used immediately, without further purification.
delta(H) (90 MHz) 3.7 (3H, s, COOCH3); 5.3 and 6.3 (each 1H, each s, CH2); 7.2-7.6 (5H, m, Ph).
{Lit. values for ethyl alpha-phenylthioacrylate;[6] delta(H) 5.13 (1H, s); 6.10 (1H, s).}
T.L.C.; Rf ~ 0.39 (10% ethyl acetate, petrol).
Methyl alpha-phenylsulphinylacrylate 7[7]
meta-Chloroperbenzoic acid (0.22 moles) was added portionwise to a solution of methyl alpha-phenylthioacrylate (crude, ~ 0.22 moles) in dichloromethane (1000 ml) at 0degC until T.L.C. analysis (neat dichloromethane) showed complete reaction. The mixture was filtered, washed with saturated sodium bicarbonate solution (4 x 1000 ml), dried (MgSO4) and concentrated in vacuo to afford the acrylate 7 (49.2 g) as a yellow low melting solid that could be used without further purification. Otherwise chromatography (dichloromethane) afforded 7 (33.2 g, 68% from 8) as a yellow low melting solid.
delta(H) 3.68 (3H, s, COOCH3); 6.78 and 6.83 (each 1H, each s, CH2); 7.40-7.62 (3H, m) and 7.66-7.74 (2H, m) (Ph).
{Lit. values; [8] delta(H) (CCl4) 3.60 (3H, s); 6.60 (2H, s); 7.15-7.80 (5H, m).}
vmax (liquid film); 3058; 2954; 1714 (alpha,beta-unsaturated ester); 1620; 1443; 1284; 1252; 1121; 1081; 1051; 754; 702; 688 cm(-1).
{Lit. values;[9] v 3060; 1710; 1610; 1580; 1470; 1440; 1050; 1020; 860; 750; 665 cm(-1).}
m/z (C.I., NH3); 228 (M + NH4+); 211 (MH+)
T.L.C.; Rf 0.13 (dichloromethane).
A portion (4.03 g) was recrystallised from petrol/ether to yield 45 in two crops (1.0 g, 0.70 g) as a pale yellow crystals.
m.p.; 40.5-4.15degC (corrected).
{Lit. m.p.;[10] 41degC.}
C10H10O3S requires C 57.13%, H 4.80%;
found C 56.98%, H 4.80%.