2536
These models have permitted us to propose an explanation for the diastereoselectivity attained in all
conditions. The reactions are very reproducible and the diastereoisomers could be easily separated by
conventional column chromatography. The preferential diastereoselectivity obtained for the silylated
adducts is the opposite of that attained in homogenous catalytic hydrogenation conditions of this type
of adduct and in our point of view these results are complementary to them. This simple and efficient
methodology associated with the readily chromatographic separation of the diastereoisomers provides
a new entry to products which are equivalent to those obtained from an aldol condensation reaction
between an aldehyde and a propionate derivative. Additional studies focusing on the generalization of
this strategy for other Baylis–Hillman adducts are ongoing in our laboratory.
Acknowledgements
We thank the Brazilian National Research Council (CNPq) for a fellowship to F.C. (CNPq 301369/87-
9) and FAPESP for financial support and a fellowship to C.R.M. (#. 98/13424-1).
References
1. Basavaiah, D.; Rao, P. D.; Hyma, R. S. Tetrahedron 1996, 52, 8001–8062.
2. Ciganek, E. In Organic Reactions; John Wiley & Sons Inc.: New York, 1997; Vol. 51, Chapter 2, pp. 201–350.
3. Brown, J. M.; Cutting, I. J. Chem. Soc., Chem. Commun. 1985, 578–579.
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6. Yamamoto, K.; Takagi, M.; Tsuji, J. Bull. Schem. Soc. Jpn. 1988, 319–321.
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8. Sato, S.; Matsuda, I.; Shibata, M. J. Organomet. Chem. 1989, 377, 347–356.
9. Almeida, W. P.; Coelho, F. Tetrahedron Lett. 1998, 39, 8609–8612.
10. Standard experimental protocol: To a suspension of Pd–C 5% (5 mol%) in ethyl acetate (3mL) was added under nitrogen
atmosphere a solution of the adduct (0.1–0.3 mmol) in 3 mL of ethyl acetate. Then the atmosphere reaction was changed
for hydrogen and the reaction was maintained for 2–3 h under stirring at room temperature (for the acetylated adducts the
reaction was stopped after 30 min). After that the reaction was filtrated over a pad of Celite and the solvent was removed
under reduced pressure.
11. In the hydrogenation reaction of the double bond of the nitro derivatives we have observed they were totally reduced to the
amine. However the diastereoselectivity achieved is comparable with the other examples.
12. Heathcock, C. H. In Asymmetric Synthesis; Morrison, J. D., Ed.; Academic Press: London, 1984; Vol. 3, part B, p. 115.
13. Corey, E. J.; Venkateswarlu, A. J. Am. Chem. Soc. 1972, 94, 6190–6191.
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therein.
15. Spectra data: (1H NMR, 500 MHz, CDCl3) δ 6 syn: 1.06 (d, J=6.9 Hz, 3H), 2.54–2.80 (m, 1H), 3.55 (s, 3H), 4.98 (d,
J=4.3 Hz, 1H), 7.24–7.26 (m, 5H); 6 anti: 0.90 (d, J=7.3 Hz, 3H), 2.54–2.80 (m, 1H), 3.63 (s, 3H), 4.65 (d, J=8,5 Hz, 1H),
7.24–7.26 (m, 5H); 7 syn: 1.13 (d, J=6.9 Hz, 3H), 2.58–2.82 (m, 1H), 3.62 (s, 3H), 3.78 (s, 3H), 4.97 (d, J=5.1 Hz, 1H),
6.85–6.88 (m, 2H), 7.23 (d, J=8.7 Hz, 2H); 7 anti: 0.95 (d, J=6.9 Hz, 3H), 2.58–2.82 (m. 1H), 3.71 (s, 3H), 3.78 (s, 3H),
4.67 (d, J=8.7 Hz, 1H), 6.85–6.88 (m, 2H), 7.23 (d, J=8.7 Hz, 2H); 8 syn: 1.11 (d, H=6.9 Hz, 3H), 2.58–2.82 (m, 1H), 3.64
(s, 3H), 5.02 (d, J=4.3 Hz, 1H), 7.25–7.34 (m, 4H); 8 anti: 0.97 (d, J=7.3 Hz, 3H), 2.58–2.82 (m, 1H), 3.69 (s, 3H), 4.70
(d, J=8.4 Hz, 1H), 7.25–7.34 (m, 1H); 9 syn: 1.15 (d, J=7.1 Hz, 3H), 2.70–2.82 (m, 1H), 3.64 (s, 3H), 4.94 (d, J=4.6 Hz,
1H), 6.64–6.67 (dd, J= 8.5 and 2.7 Hz, 2H), 7.12 (d, J=7.9 Hz, 2H); 9 anti: 0.97 (d, J=7.4 Hz, 3H), 2.70–2.82 (m, 1H), 3.73
(s, 3H), 4.64 (d, J=8.7 Hz, 1H), 6.64–6.67 (dd, J=8.5 and 2.7 Hz, 2H), 7.12 (d, J=7.9 Hz, 2H); 10 syn: 1.13 (d, J=7.1 Hz,
3H). 2.70–2.78 (m, 1H), 3.65 (s, 3H), 4.96 (d, J=4.3 Hz, 1H), 5.94 (s, 2H), 6.84 (s, 3H); 10 anti: 0.97 (d, J=7.1 Hz, 3H),
2.70–2.78 (m, 1H), 3.04 (broad s, exchangeable with D2O), 3.72 (s, 3H), 4.65 (d, J=8.7 Hz, 1H), 5.94 (s, 2H), 6.84 (s, 3H).
16. (a) Hoffmann, R. W. Chem. Rev. 1989, 89, 1841–1860; (b) Kahn, S. D.; Pau, C. F.; Chamberlin, A. R.; Hehre, W. J. J. Am.
Chem. Soc. 1987, 109, 650–663 and references cited therein.