Lewis Acid-Promoted Generation of an Iminium ion from Ethyl 2-(N-Benzyloxycarbonylamino)-methylene-3-oxobutanoate and Its Reactions with Ketene Silyl Acetals

Synlett

Volumn 1996, Issue 11, 1996, Pages 1103-1105

  Saito, Seiki ^a   Uedo, Eiji ^a   Kato, Yoshitaka ^a   Murakami, Yoshinori ^a   Ishikawa, Teruhiko ^a  

^a OKAYAMA UNIVERSITY   (Japan)

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Indexed keywords

EID: 0008861249     PISSN: 09365214     EISSN: None     Source Type: Journal    
DOI: 10.1055/s-1996-5690     Document Type: Article

References (16)

1. (a) Blicke, F. F. Org. React. 1942, 1, 303.
2. (b) Reichert, B. "Die Mannich Reaktion", Springer-Verlag, Berlin, 1959,
3. (c) Tramontini, M. Synthesis, 1973, 703.
4. Kleinman, E. F. in Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Heathcock, C. H., Eds.; Pergamon Press: New York, 1991; Vol. 2, p. 893.
5. Overman, L. E.; Ricca, N. J. in Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Heathcock, C. H., Eds.; Pergamon Press: New York, 1991; Vol. 2, p. 1007.
6. 4 to an imine nitrogen atom, see Kercher, T.; Livinghouse, T. J. Am. Chem. Soc. 1996, 118, 4200.
7. 4 to an imine nitrogen atom, see Kercher, T.; Livinghouse, T. J. Am. Chem. Soc. 1996, 118, 4200.
8. 4 to an imine nitrogen atom, see Kercher, T.; Livinghouse, T. J. Am. Chem. Soc. 1996, 118, 4200.
9. Prepared by the addition-elimination sequence of benzyl carbamate and ethyl 2-(methoxy)methyleneacetoacetate, the latter of which was derived from ethyl acetoacetate in the usual way after an appropriate Knoevenagel protocol; Gaudry, M.; Jasor, Y.; Khac, T. B. Org. Synth. 1979, 59, 153.
10. 2) are required, in particular when the catalytic amount of the Lewis acid is employed. On the other hand, when a colorless solution resulted, the reaction became deteriorated to give only 30% or less yield.
11. 13C-signal of the keto-carbonyl group of 1 appears at 199.9 ppm: this is considerably low-field in the light of its conjugated structure because that of a hydrogen bond-lacking structure such as ethyl 2-(N,N-diethylamino)methylene-3-oxobutanoate appears at 194.7 ppm.
12. 13C-NMR (126 MHz) δ 14.1, 14.3, 14.4, 22.4, 23.0 (m), 24.7, 26.3, 26.5, 27.4, 27.7, 58.0, 59.8, 99.1, 114.9, 127.0, 127.9, 129.7, 141.0, 158.8, 165.7, 187.7.
13. 3N/70°C) was observed.
14. 2.
15. The table contains both catalytic and stoichiometric results. In general, the latter cases are more reproducible than the catalytic cases which, of course, become reproducible when the conditions as indicate in ref. 5 are satisfied.
16. 1H-NMR (200 MHz) δ 1.18 (d, 1.5H), 1.22 (d, 1.5H), 2.14 (s, 3H), 2.57-2.94 (m, 3H), 3.66 (s, 1.5H), 3.67 (s, 1.5H), 4.10-4.29 (m, 1H), 5.09 (s, 2H), 5.49 (bs, 0.5H), 5.62 (bs, 0.5H), 7.34 (s, 5H).