Lastly the timing of the two processes, anionic charge
development on Cβ and hydrogen bonding to the Cβ, is rather
difficult to clearly envisage. These two would not take place in
the absence of N–Cα bond formation. The electronic shift to
form an anionic center should follow immediately and then a
proton shift to Cβ. Since both shifts, electron and proton, are
fast, at best these two could conceivably occur synchronously
with bond formation.
reduced, and two new peaks for CH–CH in the product,
p-CH3OC6H4(MeOC6H4CH2NH)CH–CH(COCH3)CO2C2H5,
grew at 3.46 and 4.77 ppm as the reaction proceed. No other
peaks or complications were found during the reaction except
the 3 peak height changes indicating that the reaction proceeds
with no other side reactions.
Acknowledgements
This work was supported by a Korea Research Foundation
Grant (KRF-2002-070-C00061).
Experimental
Materials
References
Merck GR acetonitrile was used after three distillations.
The benzylamine nucleophiles, Aldrich GR, were used after
recrystallization.
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Preparation of ethyl ꢀ-acetyl-ꢁ-phenylacrylates
The ethyl α-acetyl-β-phenylacrylates were prepared by the
literature method of Horning et al.10 Equimolecular amounts
of benzaldehyde (10 mmol) and ethyl acetoacetate(10 mmol)
were dissolved in the minimal amount of pyridine and refluxed
for 1 h. Solvent was removed under reduced pressure and
product was separated by column chromatography (silica gel,
10% ethylacetate-n-hexane) (yield >85%). IR (Nicolet 5BX
1
FT-IR) and H and 13C NMR (JEOL 400 MHz) data were
found to agree well with the literature values.10
Kinetic measurements
The reaction was followed spectrophotometrically by monitor-
ing the decrease in the concentration of ethyl α-acetyl-β-phenyl-
acrylate, [EAP], at λmax of the substrate to over 80% com-
pletion. The reaction was studied under pseudo-first-order
conditions, [EAP] = 8.0 × 10Ϫ5 M and [BA] = 0.02–0.05 M at
25.0 0.1 ЊC. The pseudo first-order rate constant, kobs, was
determined from the slope of the plot (r > 0.995) ln[EAP]
(2.303 log [EAP ] vs. time. Second-order rate constants, kN, were
obtained from the slope of a plot (r > 0.993) of kobs vs. benzyl-
amine with more than four concentrations of more than three
runs and were reproducible to within 3%.
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Product analysis
The analysis of final products was difficult due to partial
decomposition during product separation and purification. We
therefore analysed the reaction mixture by NMR (JEOL 400
MHz) at appropriate intervals under exactly the same reaction
conditions as the kinetic measurement in MeCN at 25.0 ЊC.
Initially we found a peak for CH in the reactant, p-CH3OC6-
10 E. C. Horning, M. S. Fish and G. N. Walker, Org. Synth., 1983, 4,
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11 (a) C. Hansch, A. Leo and R. W. Taft, Chem. Rev, 1991, 91, 165;
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1998, 19, 1198.
12 K. B. Wiberg, Physical Organic Chemistry, Wiley, New York, 1964,
p. 378.
H CH᎐C(COCH )CO C H , at 7.48 ppm, which was gradually
᎐
4
3
2
2
5
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2, 1 2 1 3 – 1 2 1 6
1216