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hexanes-EtOAc, 19 : 1 to 4 : 1, v/v) afforded 61 (900 mg, 60%, 2 steps) as a 1 : 1 mixture of
diastereomers.
1 H NMR (300 MHz, CDCl3): δ 7.84-7.81 (m, 2H), 7.62-7.44 (m, 3H), 6.98 (d, J = 7.5 Hz, 1H),
5.61-5.44 (m, 1H), 4.97-4.86 (m, 1H), 4.23-4.17 (m, 1H), 4.00-3.96 (m, 1H), 2.49 (d, J = 2.1 Hz,
0.5H), 2.46 (d, J = 2.1 Hz, 0.5H), 1.57 (d, J = 5.7 Hz, 1.5H), 1.55 (d, J = 5.7 Hz, 1.5H), 0.89 (s,
4.5H), 0.88 (s, 4.5H), 0.07 (s, 1.5H), 0.06 (s, 1.5H), 0.04 (s, 1.5H), 0.04 (s, 1.5H); 13 C NMR (75
MHz, CDCl3): δ 169.5, 169.4, 167.0, 166.9, 134.0, 131.8, 128.7, 127.0, 81.5, 81.4, 73.6, 73.5,
63.5, 63.4, 61.5, 61.4, 54.7, 54.5, 25.8, 25.7, 21.3, 21.2, 18.2, 18.1, -5.5, -5.6; IR (thin film): ν
3442, 3310, 2930, 2121, 1747, 1665, 1109 cm -1 ; MS m/z (%) 360 (42), 318 (35), 105 (100); EI
HRMS calcd for C20H29NO4Si m/z [M] + 375.1866, found 375.1852.
MeO 2C
2-Benzoylamino-2-(tert-butyldimethylsilyloxymethyl)hexa-3,4-dienoic acid methyl ester
(58i). To a solution of propargyl ester 61 (730 mg, 1.95 mmol) in MeCN (10 mL), were added in
consecutive order Et3N (758 µL, 5.45 mmol), CCl4 (430 µL, 4.49 mmol) and PPh3 (1.12 g, 4.29
mmol) at rt. After 3 h the starting material was consumed based upon TLC analysis. The solution
was concentrated under vacuum to a viscous brown paste which was next dissolved in MeOH
(10 mL). Then, Et3N (500 µL) was added and after 3 h the solution was again concentrated under
vacuum. The crude residue was diluted with EtOAc (50 mL), and the solution was poured in an
Erlenmyer flask, and then hexanes (20 mL) were added under vigorous stirring. The resulting
mixture was filtered through a plug of silica gel using a fritted funnel, and eluted with
hexanes/Et2O (1 : 1). The filtrate was concentrated under vacuum and the residue was purified by
•
H
NHBz
58i
153
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