LETTER
N-Vinyl-2-Oxazolidinone
955
1633 (C=C), 1248, 1080 (C-O) cm–1; 1H NMR (400 MHz,
CDCl3), 3.72 (t, 2 H, J4 -5 = 8.2 Hz, H-4 ), 4.30 (dd, 1 H,
References and Notes
(1) (a) Boger, D. L.; Weinreb, S. N. Hetero Diels–Alder
Methodology in Organic Synthesis; Academic Press: San
Diego, 1987. (b) Tietze, L. F.; Kettschau, G. Top. Curr.
Chem. 1997, 189, 1.
J
2B-1 = 15.8 Hz, JAB = 1.0 Hz, H-2B), 4.44 (dd, 1 H, J2A-1
8.9 Hz, JAB = 1.0 Hz, H-2A), 4.47 (t, 2 H, J5 -4 = 8.2 Hz, H-
5 ), 6.89 (dd, 1 H, J1-2B = 15.8 Hz, J1-2A = 8.9 Hz, H-1); 13
=
C
NMR(100 MHz, CDCl3), 41.7 (C-4 ), 62.0 (C-5 ), 93.3 (C-
2), 129.7 (C-1), 155.2 (C-2 )..
(2) For reviews, see: (a) Rappoport, Z. The Chemistry of
Enamines in The Chemistry of Functional Groups; John
Wiley and Sons: New York, 1994. (b) Whitesell, J. K.;
Whitesell, M. A. Synthesis 1983, 517. (c) Hickmott, P. W.
Tetrahedron 1982, 38, 1975. (d) Hickmott, P. W.
Tetrahedron 1982, 38, 3363. (e) Lenz, G. R. Synthesis 1978,
489. (f) For reviews on cycloaddition using dienamides, see:
Campbell, A. L.; Lenz, G. R. Synthesis 1987, 421.
(3) For recent studies involving enamides, see: (a) Fuchs, J. R.;
Funk, R. L. Org. Lett. 2001, 3, 3349. (b) Maeng, J.-H.;
Funk, R. L. Org. Lett. 2001, 3, 1125. (c) Abbiati, G.;
Clerici, F.; Gelmi, M. L.; Gambini, A.; Pilati, T. J. Org.
Chem. 2001, 66, 6299. (d) Bach, T.; Schröder, J.; Brandl, T.;
Hecht, J.; Harms, K. Tetrahedron 1998, 54, 4507.
(4) For recent examples of synthesis and cycloadditions of
dienamides, see: (a) Gauvry, N.; Huet, F. J. Org. Chem.
2001, 66, 583. (b) von Wangelin, A. J.; Neumann, H.;
Gordes, D.; Spannenberg, A.; Beller, M. Org. Lett. 2001, 3,
2895. (c) Ha, J. D.; Kang, C. H.; Belmore, K. A.; Cha, J. K.
J. Org. Chem. 1998, 63, 3810; and references 1–7 cited
therein.. (d) For epoxydation of enamides, see: Adam, W.;
Reinhardt, D.; Reissig, H.-U.; Paulini, K. Tetrahedron 1995,
51, 12257; and references cited therein. (e) Also see:
Koseki, Y.; Kusano, S.; Ichi, D.; Yoshida, K.; Nagasaka, T.
Tetrahedron 2000, 56, 8855.
(5) The first examples of inverse-electron demand [4+2]
heterocycloadditions of allenamides and allenimides
(including chiral ones) were recently described: (a) Wei, L.-
L.; Xiong, H.; Douglas, C. J.; Hsung, R. P. Tetrahedron Lett.
1999, 40, 6903. (b) Wei, L.-L.; Hsung, R. P.; Xiong, H.;
Mulder, J. A.; Nkansah, N. T. Org. Lett. 1999, 1, 2145.
(6) Vani, P. V.; Chida, A. S.; Srinivasan, R.; Chandrasekharam,
M.; Singh, A. K. Synth. Commun. 2001, 31, 2043.
(7) Walles, W. E.; Tousignant, W. F.; Houtman, T. US Patent
Appl. 2891058, 1959.
(8) Tulshian, D. B.; Tsang, R.; Fraser-Reid, B. J. Org. Chem.
1984, 49, 2347.
(9) Dujardin, G.; Rossignol, S.; Brown, E. Tetrahedron Lett.
1995, 36, 1653.
(10) Akiba, T.; Tamura, O.; Hashimoto, M.; Kobayashi, Y.;
Katoh, T.; Nakatani, K.; Kamada, M.; Hayakawa, I.;
Terashima, S. Tetrahedron 1994, 50, 3905.
(11) Gassman, P. G.; Burns, S. J.; Pfister, K. B. J. Org. Chem.
1993, 58, 1449.
(14) General preparation of hetero-adduct 4a–f with Eu(fod)3: A
solution of heterodiene 3 (0.5 mmol), N-vinyl-2-oxazol-
idinone 1 (0.5 mmol) and Eu(fod)3 (0.025 mmol) in cyclo-
hexane (5 mL) was refluxed under nitrogen for the time
referred to Table 2. After removal of solvent the crude
product was chromatographed (silica gel 40/1) using
cyclohexane–AcOEt, 70:30 to 50:50. Compounds 4a–f
obtained with yields referred to Table 2 are new and
analytical data of one representative example is included in
ref. 15.
(15) Analytical data of hetero-adduct 4a cis: white crystal, mp
59–61 °C(ether); Rf = 0.23 (cyclohexane–AcOEt, 1:1); 1H
NMR (400 MHz, CDCl3), 1.94 (dt, 1 H, JAB = 12.8 Hz,
J2ax-3 = J2ax-1 = 11.3 Hz, H-2ax), 2.26 (ddt, 1 H, JAB = 12.8 Hz,
J2eq-3 = 6.4 Hz, J2eq-1 = J2eq-4 = 2 Hz, H-2eq), 3.57 (dt, 1 H, JAB
= J4 B-5 B = 8.9 Hz, J4 B-5 A = 6.2 Hz, H-4 B), 3.81 (s, 3 H,
OCH3), 3.84 (m, 1 H, H-4 A), 3.89 (ddd, 1 H, J3-2ax = 11.3 Hz,
J3-2eq = 6.4 Hz, J3-4 = 2.5 Hz, H-3), 4.38 (dt, 1 H, JAB = J5 B-
4 B = 8.9 Hz, J5 B-4 A = 6.9 Hz, H-5 B), 4.46 (dt, 1 H, JAB = J5 A-
4 A = 8.9 Hz, J5 A-4 B = 6.2 Hz, H-5 A), 5.76 (dd, 1 H, J1-2ax
=
11.3 Hz, J1-2eq = 2 Hz, H-1), 6.17 (t, 1 H, J4-3 = J4-2eq = 2 Hz,
H-4), 7.22 (d, 2 H, J = 6.9 Hz, Ho), 7.29 (t, 1 H, J = 7.4 Hz,
Hp), 7.35 (t, 2 H, J = 7.4 Hz, Hm); 13C NMR (100 MHz,
CDCl3), 35.5 (C-2), 39.5 (C-3), 40.1 (C-4 ), 52.7 (OCH3),
62.9 (C-5 ), 81.3 (C-1), 114.6 (C-4), 127.5 (Co), 127.7 (Cp),
129.3 (Cm), 142.5 (Cn), 144.4 (C-5), 157.8 (C-2 ), 163.0
(CO2). IR(film): 1758 (C=O), 1643 (C=C), 1134, 1248, 1288
(C-O) cm–1; SM C16H17NO5 [M]+· 303 (1.8%); HRMS (EI)
calcd for C16H15NO4 [M-H2O]+ 285.1001, found 285.1008.
(16) Preparation of hetero-adduct 4a trans with SnCl4: To a
cooled solution (–78 °C) of heterodiene 3a (95 mg, 0.5
mmol) and N-vinyl-2-oxazolidinone 1 (57 mg, 0.5 mmol) in
anhydrous CH2Cl2 (5 mL) under nitrogen was added
dropwise SnCl4 1 M in CH2Cl2 (0.25 mL, 0.25 mmol). After
stirring (5 min) the mixture was quenched with sat. aq.
NaHCO3 (5 mL). After returning to r.t. and extraction with
CH2Cl2 (2 5 mL), the resulting organic layer was dried
(MgSO4). Removal of solvent and purification by
chromatography (silica gel 40/1; cyclohexane–AcOEt,
70:30 to 50:50) yielded 4a (143 mg, 94%) as a mixture cis/
trans, 68:32. 4a trans was thus isolated as a white solid; Rf
= 0.16 (cyclohexane–AcOEt, 1:1); 1H NMR (400 MHz,
CDCl3), 2.03 (dq, 1 H, JAB = 13.3 Hz, J2eq-1 = J2eq-3
=
(12) Bach, T.; Brummerhop, H. J. Prakt. Chem. 1999, 341, 410.
(13) Preparation of N-vinyl-2-oxazolidinone 1: A mixture of
oxazolidinone (2.05 g, 23.4 mmol), acetaldehyde diethyl
acetal (33 mL, 0.23 mol) and D,L-camphorsulfonic acid
(0.27 g, 1.17 mmol) was heated for 15 h at 55 °C. After
cooling, aq. NaHCO3 (15 mL) was added and the reaction
mixture extracted with Et2O (3 8 mL). The organic layer
was washed with brine and dried over MgSO4. Removal of
solvent yielded crude N,O-acetal 2 (3.72 g, quantitative)
used without further purification. To a cooled solution (0 °C)
of crude N,O-acetal 2 (3.72 g, 23.4 mmol) in anhydrous
CH2Cl2 under nitrogen (22 mL) were dropwise added
distilled NEt3 (4.9 mL, 37.7 mmol) and, trimethylsilyl
triflate (5.5 mL, 30.4 mmol). After slow return to r.t. and
stirring for 16 h, the mixture was filtered on basic alumina.
Removal of solvent and purification by filtration (silica gel
4/1; ether) yielded 1 (1.95 g, 73%) as a pale yellow oil;
Rf = 0.37 (Cyclohexane–AcOEt, 1:1); IR(film): 1753 (C=O),
J2eq-4 = 2 Hz, H-2eq), 2.33 (ddd, 1 H, JAB = 13.3 Hz, J2ax-1
11.3 Hz, J2ax-3 = 6.6 Hz, H-2ax), 3.61 (dt, 1 H, JAB = J4 B-5 B
=
=
8.6 Hz, J4 B-5 A = 5.9 Hz, H-4 B), 3.81 (m, 2 H, H-3 + H-4 A),
3.83 (s, 3 H, OCH3), 4.34 (q, 1 H, JAB = J5 B-4 B = J5 B-4 A = 8.5
Hz, H-5 B), 4.42 (dt, 1 H, JAB = J5 A-4 A = 8.9 Hz, J5 A-4 B = 5.9
Hz, H-5 A), 5.43 (dd, 1 H, J1-2ax = 11.3 Hz, J1-2eq = 2.2 Hz,
H-1), 6.25 (dd, 1 H, J4-3 = 5.3 Hz, J4-2eq = 1.5 Hz, H-4), 7.23
(d, 2 H, J = 6.9 Hz, Ho), 7.27 (t, 1 H, J = 5.9 Hz, Hp), 7.35 (t,
2 H, J = 7.4 Hz, Hm); 13C NMR (100 MHz, CDCl3), 33.8
(C-2), 37.1 (C-3), 40.5 (C-4 ), 52.7 (OCH3), 62.8 (C-5 ), 77.7
(C-1), 111.9 (C-4), 127.6 (Cp), 128.4 Co), 129.3 (Cm), 143.2
(Cn), 144.7 (C-5), 157.8 (C-2 ), 163.1 (CO2).
(17) A similar gap of reactivity was previously observed between
4a and 4d–e towards ketone enol ethers as the dienophiles:
Martel, A.; Leconte, S.; Dujardin, G.; Brown, E.;
Maisonneuve, V.; Retoux, R. Eur. J. Org. Chem. 2002, 3,
514.
Synlett 2002, No. 6, 952–956 ISSN 0936-5214 © Thieme Stuttgart · New York