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HETEROCYCLES, Vol. 71, No. 1, 2007
13
1H), 5.08 (s, 2H), 5.50 (d, J = 15.0 Hz, 1H), 7.27-7.47 (m, 10H); C NMR (100 MHz, CD3CN) δ 45.6,
°
49.0, 59.2, 63.2, 127.6, 127.9, 128.2, 128.3, 128.4, 129.0, 135.1, 135.6, 172.1, 183.6; mp 122-124 C;
HRMS found 326.1097 +/- 0.0010 (calc. 326.1089)
1,3-Dibenzyl-5-methylene-2-thioxoimidazolidin-4-one (11): A suspension of 9 (858 mg, 2.62 mmol,
1.0 equiv) in dichloromethane (15 mL) was cooled to 0 oC, triethylamine (913 µL, 6.55 mmol, 2.5 equiv)
added, then methanesulfonyl chloride (304 µL, 3.94 mmol, 1.5 equiv) was added slowly, dropwise. The
o
solution was stirred at 0 C for 45 min, diluted with ether, washed with saturated ammonium chloride,
then brine. The organic phase was dried over sodium sulfate, filtered, and concentrated in vacuo to afford
1
a yellow oil (808 mg, 99% yield): IR (KBr) 3032, 1740, 1648, 1346, 1233, 879; H NMR (300 MHz,
CDCl3) δ 4.88 (d, J = 2.7 Hz, 1H), 5.13 (s, 2H), 5.24 (s, 2H), 5.44 (d, J = 2.7 Hz, 1H), 7.22-7.35 (m, 8H),
13
7.49 (dd, J = 7.7 Hz, 1.7 Hz, 2H); C NMR (75 MHz, CDCl3) δ 45.5, 47.6, 98.5, 127.1, 127.9, 128.0,
128.5, 128.8, 128.9, 134.6, 135.4, 135.6, 162.5, 179.1; HRMS found 308.0990 +/- 0.0009 (calc.
308.0983).
3-Benzyl-5-(hydroxymethyl)-2-thioxoimidazolidin-4-one (10): A suspension of serine methyl ester,
hydrochloride (8) (1.17 g, 7.5 mmol, 1.0 equiv), benzyl isothiocyanate (1.0 mL, 7.5 mmol, 1.0 equiv), and
triethylamine (1.05 mL, 7.5 mmol, 1.0 equiv) was refluxed in dichloromethane (25 mL) for 5 h then
o
cooled to 23 C. The solution was diluted with ethyl acetate and washed twice with saturated
ammonium chloride, then brine, then dried over anhydrous sodium sulfate, filtered, and concentrated in
vacuo. The residue was washed with some cold ether to remove residual benzyl isothiocyanate
affording white spheres of analytical purity (2.61 g, 55% yield): IR (KBr) 3394, 3200, 1708, 1347, 1242;
1H NMR (400 MHz, CD3CN) δ 3.35 (t, J = 5.8 Hz, 1H), 3.82-3.87 (m, 2H), 4.19-4.21 (m, 1H), 4.95 (s,
13
2H), 7.24-7.33 (m, 5H), 8.12 (bs, 1H); C NMR (100 MHz, CD3CN) δ 44.8, 61.1, 62.7, 128.1, 128.2,
o
129.2, 137.3, 174.0, 185.3; mp 139-140 C; C,H,N Anal. Calcd for C11H12N2O2S: C 55.91, H 5.12, N
11.86. Found: C 55.89, H 4.92, N 11.71.
3-Benzyl-5-methylene-2-thioxoimidazolidin-4-one (12): A suspension of 10 (424 mg, 1.79 mmol, 1.0
o
equiv) in dichloromethane (25 mL) was cooled to 0 C, triethylamine (1.25 mL, 8.95 mmol, 5.0 equiv)
was added, then trifluoroacetic anhydride (760 µL, 5.38 mmol, 3.0 equiv) added slowly, dropwise. The
o
solution was stirred at 0 C for 1 h, diluted with ether, washed with saturated sodium bicarbonate, then
saturated ammonium chloride, then brine. The organic phase was dried over anhydrous sodium sulfate,
filtered, and concentrated in vacuo to afford a yellow oil which was purified by flash column
chromatography on silica gel using gradient elution (hexanes → 20/80 ethyl acetate-hexanes) to give a
1
shiny, pale-yellow solid (258 mg, 66% yield): IR (KBr) 3423, 2951, 1706, 1659, 1313, 1233; H NMR
(400 MHz, CDCl3) δ 5.05 (s, 2H), 5.06 (d, J = 2.0 Hz, 1H), 5.46 (d, J = 2.0 Hz, 1H), 7.20-7.33 (m, 3H),
13
7.45-7.51 (m, 2H), 8.19 (bs, 1H); C NMR (75 MHz, CDCl3) δ 44.7, 98.2, 127.9, 128.5, 128.7, 133.9,