Download (3249Kb) - D-Scholarship@Pitt - University of Pittsburgh

General procedure B for the Claisen rearrangement via an oxazole.
MeO2C Bz
N
H
58d
2-Benzoylamino-2-isobutylpenta-3,4-dienoic acid methyl ester (58d). To a solution of
propargyl ester 56d (36.5 g, 134.0 mmol) in MeCN (500 mL), were added successively Et3N (78
mL, 560 mmol), CCl4 (45 mL, 470 mmol) and PPh3 (109 g, 414 mmol) all at rt. After 2.5 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 (50 mL). Then, sat’d
solution of HCl in MeOH (10 mL, prepared by bubbling HCl gas through MeOH) was added and
the reaction was stirred for additional 10 min. The solvents were removed using a rotary
evaporator and the resulting viscous oil was dispersed in Et2O (200 mL) and poured in a 1 L
Erlenmeyer flask. Hexanes (400 mL) were added under vigorous stirring and a yellow precipitate
formed. Filtration of the mixture over a plug of silica gel using a fritted funnel was followed by
rinsing with hexanes/Et2O (1 : 1). The filtrate was concentrated under vacuum and the crude
residue was purified by silica gel chromatography (hexanes-EtOAc, 6 : 1 to 3 : 1, v/v) to give
58d (23.8 g, 62%) as a white solid (mp range 68-69 °C).
1 H NMR (300 MHz, CDCl3): δ 7.77-7.74 (m, 2H), 7.44-7.35 (m, 3H), 7.23 (s, 1H), 5.57 (t, J =
6.6 Hz, 1H), 4.92 (d, J = 6.6 Hz, 2H), 3.75 (s, 3H), 2.47 (dd, J = 14.2, 5.5 Hz, 1H), 2.05 (dd, J =
14.2, 5.5 Hz, 1H), 1.65 (sept, J = 6.5 Hz, 1H), 0.89 (d, J = 6.6 Hz, 3H), 0.81 (d, J = 6.6 Hz, 3H);
13 C NMR (75 MHz, CDCl3): δ 206.4, 173.1, 165.9, 134.4, 131.3, 128.3, 126.7, 93.9, 79.7, 61.5,
52.6, 42.7, 24.5, 23.6, 22.6; IR (thin film): ν 3319, 2956, 1958, 1742, 1651, 1526, 1486 cm -1 ; MS
m/z (%) 287 (33), 228 (55), 105 (100); EI-HRMS calcd for C17H21NO3 m/z [M] + 287.1521; found
287.1535.
148
•