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15 min the solvent was removed under vacuum and the remaining residue was dissolved in
EtOAc and filtered through a plug of silica gel on a fritted funnel eluting with EtOAc/hexanes (1
: 1). Concentration of the solution under vacuum afforded an orange oil that was purified by
flash chromatography (hexanes-EtOAc, 6 : 1, v/v) to afford 145b (0.170 g, 82%).
1 H NMR (300 MHz, CDCl3): δ 7.38-7.28 (m, 3H), 7.21-7.13 (m, 2H), 6.61 (s, 1H), 5.51 (dq, J =
6.3, 3.2 Hz, 1H), 5.45 (quin, J = 6.5 Hz, 1H), 3.87 (s, 3H), 3.69 (d, J = 13.7 Hz, 1H), 3.47 (d, J =
13.7 Hz, 1H), 2.84 (s, 1H), 1.77 (dd, J = 7.0, 3.2 Hz, 3H); 13 C NMR (75 MHz, CDCl3): δ 203.2,
171.4, 150.8, 135.3, 129.9, 128.2, 127.0, 92.1, 91.8, 77.2, 72.8, 63.9, 52.9, 39.6, 13.7; IR (thin
film): ν 3392, 3271, 2950, 2110, 1968, 1740, 1662 cm -1 ; EI-HRMS calcd for C17H17NO3 m/z
[M] + 283.1208; found 283.1198.
O
HN
MeO 2C Bn
Methyl 2-(3-(trimethylsilyl)propiolamido)-2-benzylhexa-3,4-dienoate (145c). To a solution of
3-(trimethylsilyl)propiolic acid (74 mg, 520 µmol) in THF (6 mL), was added N-
methylmorpholine (0.21 mL, 1.9 mmol) at rt. The solution was then cooled to -10 °C and
isobutyl chloroformate (68 µL, 520 µmol) was added. After 30 min at -10 °C amine 152 (110
mg, 480 µmol) in THF (4 mL) was added and the reaction was allowed to warm to rt, then stirred
for additional 3 h. The reaction was quenched with sat’d aq. NaHCO3 (50 mL) and the aqueous
layer was extracted with EtOAc. The combined organic layers were washed with brine, dried
over MgSO4 and concentrated under vacuum. Purification of the residue by column
chromatography (hexanes-EtOAc, 19 : 1, v/v) afforded 145c (121 mg, 72%).
1 H NMR (300 MHz, CDCl3): δ 7.45-7.35 (m, 3H), 7.26-7.19 (m, 2H), 6.61 (s, 1H), 5.59 (dq, J =
6.3, 3.2 Hz, 1H), 5.55–5.45 (m, 1H), 3.93 (s, 3H), 3.79 (d, J = 13.7 Hz, 1H), 3.52 (d, J = 13.6 Hz,
•
145c
203
TMS
H