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MeO2C Bz
N
H
58c
2-Benzoylamino-2-methylpenta-3,4-dienoic acid methyl ester (58c). To a solution of ester 56c
(15.5 g, 67.1 mmol) in MeCN (300 mL), were added successively Et3N (39.0 mL, 282 mmol),
CCl4 (23.0 mL, 235 mmol) and PPh3 (54.5 g, 208 mmol) all at rt. After 2.5 h the starting material
was consumed based on TLC analysis, and MeOH (1 mL) was added. The dark brown solution
was poured in a 1 L Erlenmeyer flask and hexanes (300 mL) were added under vigorous stirring.
During the addition, a viscous precipitate formed which was filtered over a plug of silica gel
using a fritted funnel and eluted 2-3 times with hexanes/Et2O (1 : 1). The filtrate was
concentrated under vacuum and the resulting residue dissolved in MeOH (50 mL) and a sat’d
solution of HCl in MeOH (10 mL) was added. After stirring for 10 min the reaction mixture was
poured in Et2O (500 mL) and the resulting solution washed with sat’d aq. NaHCO3 (500 mL).
The organic layer was dried over MgSO4 and concentrated under vacuum. Purification of the
crude residue by flash chromatography (hexanes-EtOAc, 3 : 1, v/v) afforded 58c (6.5 g, 40%) as
a white solid (mp range 135.1-136.6 °C).
1 H NMR (300 MHz, CDCl3): δ 7.79-7.77 (m, 2H), 7.52-7.35 (m, 3H), 6.91 (bs, 1H), 5.64 (t, J =
6.6 Hz, 1H), 5.04 (d, J = 6.6 Hz, 2H), 3.78 (s, 3H), 1.78 (s, 3H); 13 C NMR (75 MHz, CDCl3): δ
206.6, 172.8, 166.4, 134.2, 131.6, 128.5, 126.9, 94.1, 80.2, 58.0, 52.9, 23.1; IR (thin film): ν
3246, 2998, 1959, 1739, 1630, 1533 cm -1 ; MS m/z (%) 245 (23), 230 (52), 186 (71), 105 (100);
EI-HRMS calcd for C14H15NO3 m/z [M] + 245.1052; found 245.1058.
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