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6.72 (d, J = 7.6 Hz, 0.5H), 6.68 (d, J = 7.6 Hz, 0.5H), 5.63 (td, J = 5.9, 2.0 Hz, 0.5H), 5.56-5.53
(m, 0.5H), 5.36-5.25 (m, 1H), 4.04-4.00 (m, 2H), 3.53-3.36 (m, 2H), 2.70 (d, J = 2.0 Hz, 0.5H),
2.63 (d, J = 2.1 Hz, 0.5H), 1.06 (s, 4.5H), 1.03 (s, 4.5H), 0.27 (s, 1.5H), 0.26 (s, 1.5H), 0.23 (s,
3H).
MeO 2C
•
Bn
H
NHBz
121a
Methyl 2-(benzamido)-2-benzyl-6-(benzyloxy)hexa-3,4-dienoate (121a). Propargylic ester
120a (100 mg, 0.234 mmol) was dissolved in MeCN (5 mL) at rt. Then, Et3N (137 µL, 0.983
mmol), CCl4 (81 µL, 0.84 mmol) and PPh3 (190 mg, 0.725 mmol) were added in consecutive
order. The reaction mixture was stirred at 40 °C for 1.5 h when MeOH (1 mL) was added and the
solution was concentrated under vacuum. The crude brown residue was dissolved in MeOH (5
mL) and Et3N (100 µL) was added and the reaction was stirred for 12 h at rt. The reaction
mixture was again concentrated under vacuum, and the crude residue was purified by flash
chromatography (hexanes-EtOAc, 4 : 1, v/v) to afford 121a (102 mg, >95%) as a mixture of
diastereomers in ~2 : 1 ratio (determined by integration of the allene proton resonances in the 1 H
NMR spectrum).
1 H NMR (300 MHz, CDCl3): δ 7.78 (d, J = 8.07 Hz, 2H), 7.60-7.19 (m, 13H), 6.96 (bs, 0.67H),
6.92 (bs, 0.33H), 5.88-5.84 (m, 0.67H), 5.79-5.75 (m, 0.33H), 5.73-5.66 (m, 0.33H), 5.62-5.56
(m, 0.67H), 4.56 (s, 1.34H), 4.46 (1/2 ABq, J = 11.2 Hz, 0.33H), 4.41 (1/2 ABq, J = 11.2 Hz,
0.33H), 4.20-4.14 (m, 1.34H), 4.06-4.02 (m, 0.66H), 3.91 (s, 1H), 3.90 (s, 2H), 3.84-3.62 (m,
2H).
195
OBn