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O
HN
MeO 2C Bn
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145a
Methyl 2-benzyl-2-(but-2-ynamido)hexa-3,4-dienoate (145a). To a solution of 2-butynoic acid
(0.34 g, 4.08 mmol) in THF (25 mL), was added N-methylmorpholine (1.12 mL, 10.2 mmol) at
rt. The solution was then cooled to -10 °C with a NaCl/ice bath and isobutyl chloroformate (0.53
mL, 4.08 mmol) was added. After 30 min at -10 °C, amine 152 (0.78 g, 3.40 mmol) in THF (15
mL) was added and the reaction was allowed to warm to rt and stirred for 3 h. The reaction was
quenched with sat’d aqueous NaHCO3 and the aqueous layer was extracted twice 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, 9 : 1, v/v)
afforded 145a (0.86 g, 85%).
1 H NMR (300 MHz, CDCl3): δ 7.37-7.30 (m, 3H), 7.19-7.16 (m, 2H), 6.42 (s, 1H), 5.51 (sex, J =
3.1 Hz, 1H), 5.41 (quin, J = 7.0 Hz, 1H), 3.86 (s, 3H), 3.68 (d, J = 13.6 Hz, 1H), 3.48 (d, J = 13.6
Hz, 1H), 1.99 (s, 3H), 1.77 (dd, J = 7.1, 3.1 Hz, 3H); 13 C NMR (75 MHz, CDCl3): δ 203.1,
171.7, 152.2, 135.6, 130.1, 128.1, 126.9, 92.4, 91.6, 82.9, 74.9, 63.6, 52.8, 39.7, 13.8, 3.6; IR
(thin film): ν 3400, 3292, 2244, 1968, 1740, 1656, 1495 cm -1 ; EI-HRMS calcd for C16H16NO m/z
[M-59] + 238.1232; found 238.1230.
O
HN
MeO 2C Bn
145b
Methyl 2-benzyl-2-(propiolamido)hexa-3,4-dienoate (145b). To a solution of amine 152
(0.168 g, 0.727 mmol) in CH2Cl2 (4 mL) was added propiolic acid (0.049 mL, 0.800 mmol)
followed by DCC (0.165 g, 0.800 mmol). Formation of a white precipitate was observed. After
202
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H
H