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185 (10), 141 (21), 57 (100); EI-HRMS calcd for C12H19NO4 m/z [M] + 241.1314; found
241.1308.
72a (isomer 1): 1 H NMR (300 MHz, CDCl3): δ 7.28 (d, J = 11.7 Hz, 1H), 6.28-6.21 (m, 1H),
6.11 (bs, 1H), 5.96 (dq, J = 10.7, 7.1 Hz, 1H), 3.82 (s, 3H), 1.90 (d, J = 7.1 Hz, 3H), 1.47 (s, 9H);
13 C NMR (75 MHz, CDCl3): δ 166.0, 153.4, 134.9, 125.9, 124.4, 124.0, 80.9, 52.5, 28.3, 14.2.
72b (isomer 2): 1 H NMR (300 MHz, CDCl3): δ 6.96 (d, J = 10.9 Hz, 1H), 6.35-6.26 (m, 1H),
6.19-6.07 (m, 1H), 6.02 (bs), 3.79 (s, 3H), 1.89 (d, J = 6.4 Hz, 1H), 1.48 (s, 9H).
General procedure F for N-alkylation allenic amino-esters.
R 4
• R3 PHN
MeO2C Br
NaH, DMF, rt
R 1
R 2
R 5
PN
MeO 2C
R 1
R 4
R 5
•
73a-l
74a-i
75a-e
The following is a general procedure based on using 1.0 mmol of allenic amino ester.
To a solution of N-protected amino-ester (1.0 mmol) in DMF (4 mL), was added NaH (2.0 mmol
of 95% dry or 60% dispersion in mineral oil) in one portion at rt under nitrogen atmosphere. jj
The reaction flask was sealed with a rubber septum and after 2 min the propargyl or allyl
bromide (1.5 – 2.0 mmol) was added dropwise via a syringe. The mixture was stirred at rt for 15
- 45 min and upon completion as determined by TLC analysis, the reaction was quenched by
cautiously pouring into water (50 mL). The aqueous mixture was extracted three times with
EtOAc, the organic layers were combined, washed with brine, dried over MgSO4, and
concentrated under vacuum. Purification of the crude residue by flash chromatography (hexanes-
jj See individual compound for details. In certain cases NaH was added at 0 °C.
167
R 2
R 3