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Synlett 2008(13): 2041-2045  
DOI: 10.1055/s-2008-1077963
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Trimethylsilyl Trifluoromethanesulfonate Mediated Addition-Cyclization of N-Vinyloxazolidin-2-ones to Nitrones: An Efficient Access to 4-Substituted 5-Azaisoxazolidines

Thanh Binh Nguyen, Arnaud Martel, Robert Dhal, Gilles Dujardin*
UCO2M UMR 6011 CNRS, Université du Maine, 72085 Le Mans, France
Fax: +33(243)833344; e-Mail: gilles.dujardin@univ-lemans.fr ;
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Publication History

Received 30 April 2008
Publication Date:
15 July 2008 (online)

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Abstract

Trimethylsilyl trifluoromethanesulfonate (TMSOTf) was conveniently used to promote the reaction involving N-alken­yloxazolidin-2-ones and activated nitrones, leading to new 4-substituted 5-azaisoxazolidines in good to excellent yields. This TMSOTf-promoted procedure expanded the scope of reaction of N-vinyloxazolidin-2-ones and nitrones in complementary way to the corresponding classical 1,3-dipolar cycloaddition. Some of these adducts could not be obtained under thermal activation.

Key words

trimethylsilyl trifluoromethanesulfonate - cycloaddition - dipolarophile - nitrone - N-alkenyloxazolidinone

    References and Notes

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13

Under these conditions, the adducts between N-vinyloxazolidin-2-ones 1a,c and unactivated nitrone (R = aryl) could not be obtained due to low reactivity.

14

Dipolarophiles 1a, 1b, (Z)-1c, (Z)-1d, (E)-1e 8 and (E)-1c ¹6 were prepared according to literature reports.
Procedure for the Preparation of ( E )-3-(4-Nitrosty-ryl) oxazolidin-2-one: A solution of (Z)-1d (2.34 g, 0.1 mol), and p-toluenesulfonic acid monohydrate (50 mg) in toluene (50 mL) was refluxed for 16 h. The solution was cooled to r.t., washed with sat. aq NaHCO3 (10 mL), and dried over MgSO4. The solvent was removed. The crude product was recrystallized (CH2Cl2-n-pentane) to afford the product as a yellow solid (2.15 g, 92%); mp 170-171 ˚C (Et2O). IR (neat): 1758, 1644, 1506, 1479, 1421, 1407, 1207, 1102, 1078 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 8.14-8.18 (m, 2 H), 7.56 (d, J = 14.7 Hz, 1 H), 7.42-7.46 (m, 2 H), 5.81 (d, J = 14.7 Hz, 1 H), 4.55-4.60 (m, 2 H), 3.89-3.93 (m, 2 H). ¹³C NMR (100 MHz, CDCl3): δ = 155.1, 146.0, 142.9, 127.7, 125.6, 124.2, 108.7, 62.4, 42.3. HRMS (CI + NH3): m/z [M + H+] calcd for C11H11N2O4: 235.0719; found: 235.0718.

15

General Procedure for the Cycloaddition: At 0 ˚C, TMSOTf (222 mg, 1 mmol) was added dropwise to a mixture of nitrone 2 (1 mmol) and dipolarophile 1 (1 mmol) in chloroform (100 µL). The reaction mixture was allowed to warm to r.t., stirred for 16 h, then diluted with CH2Cl2 (25 mL) and neutralized with sat. aq NaHCO3 (10 mL). After drying (MgSO4), the solvent was removed and the crude product was purified by flash column chromatography on silica gel (cyclohexane-Et2O) to afford the corresponding adducts 4 and 3. Both diastereomers could be easily separated by conventional flash chromatography (R f,cis
> R f , trans , ΔR f ≥ 0.2; eluent: Et2O-cyclohexane, 1:1). In most cases, isolated yields of the more polar trans adduct suffered from partial loss during column chromatography purification. The results are presented in Tables  [²] and  [³] .
Physical Data of Selected Isolated Adducts:
(3 R* ,4 S* ,5 S* )-Ethyl 2-Benzyl-4-methyl-5-(2-oxooxazolidin-3-yl)isoxazolidine-3-carboxylate (3,5- cis -4b): colorless crystal; mp 65 ˚C (Et2O). IR (neat): 1736, 1191 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.25-7.35 (m, 5 H), 5.41 (d, J = 4.5 Hz, 1 H), 4.24-4.34 (m, 2 H), 4.06-4.18 (m, 2 H), 4.12 (d, J = 13.6 Hz, 1 H), 3.96 (d, J = 13.6 Hz, 1 H), 3.81-3.88 (m, 1 H), 3.74-3.69 (m, 1 H), 3.17 (d, J = 8.8 Hz, 1 H), 2.84-2.92 (m, 1 H), 1.30 (d, J = 6.8 Hz, 3 H), 1.25 (t, J = 7.1 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 169.4, 158.0, 135.9, 129.3, 128.3, 127.7, 88.0, 74.9, 62.4, 62.0, 61.5, 46.1, 41.1, 16.3, 14.1. HRMS (CI + NH3): m/z [M + H+] calcd for C17H23N2O5: 335.1607; found: 335.1603.
(3 R *,4 S *,5 S* )-Ethyl 2-Benzyl-4-methyl-5-(2-oxooxazolidin-3-yl)isoxazolidine-3-carboxylate (3,5- trans -4b): colorless crystal; mp 93 ˚C (Et2O). IR (neat): 1745, 1731, 1190 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.25-7.35 (m, 5 H), 5.44 (d, J = 5.8 Hz, 1 H), 4.30-4.34 (m, 2 H), 4.19-4.24 (m, 2 H), 4.17 (d, J = 13.6 Hz, 1 H), 4.02 (d, J = 13.6 Hz, 1 H), 3.71 (d, J = 7.8 Hz, 1 H), 3.56-3.62 (m, 1 H), 3.51-3.56 (m, 1 H), 2.84-2.93 (m, 1 H), 1.29 (d, J = 7.1 Hz, 3 H), 1.17 (t, J = 7.1 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 168.5, 157.5, 135.7, 129.3, 128.3, 127.7, 88.4, 69.6, 62.2, 61.1, 60.1, 41.5, 40.1, 14.3, 12.9. Anal. Calcd for C17H22N2O5 (334.15): C, 61.07; H, 6.63; N, 8.38. Found: C, 60.80; H, 6.72; N, 8.24.
(3 R *,4 S *,5 S* )-Ethyl 2-Benzyl-5-(2-oxooxazolidin-3-yl)-4-phenylisoxazolidine-3-carboxylate (3,5- cis -4c): colorless oil. IR (neat): 1738, 1191 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.23-7.39 (m, 10 H), 5.86 (d, J = 4.3 Hz, 1 H), 4.27-4.37 (m, 2 H), 4.23 (d, J = 13.6 Hz, 1 H), 4.10 (d, J = 13.6 Hz, 1 H), 4.01-4.13 (m, 2 H), 4.07 (dd, J = 4.3, 8.6 Hz, 1 H), 3.94-4.01 (m, 1 H), 3.88-3.94 (m, 1 H), 3.65 (d, J = 8.6 Hz, 1 H), 1.18 (t, J = 7.1 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 168.8, 157.7, 137.6, 135.5, 129.3, 129.0, 128.2, 127.8, 127.6, 127.5, 88.1, 75.8, 62.3, 61.7, 61.5, 56.5, 41.3, 13.9. HRMS (CI + NH3): m/z [M + H+] calcd for C22H25N2O5: 397.1263; found: 397.1752.
(3 R *,4 S *,5 S* )-Ethyl 2-Benzyl-5-(2-oxooxazolidin-3-yl)-4-phenylisoxazolidine-3-carboxylate (3,5- trans -4c): colorless crystal; mp 122 ˚C (Et2O). IR (neat): 1741, 1193 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.23-7.42 (m, 10 H), 5.95 (br, 1 H), 4.35 (d, J = 14.1 Hz, 1 H), 4.27-4.36 (m, 2 H), 4.00-4.06 (m, 2 H), 4.00 (d, J = 14.1 Hz, 1 H), 3.75-3.87 (m, 2 H), 3.59-3.64 (m, 2 H), 0.84 (t, J = 7.1 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 167.6, 157.1, 136.0, 135.7, 129.3, 128.7, 128.6, 128.2, 127.8, 127.6, 87.8, 70.6, 62.1, 60.8, 60.2, 52.9, 40.4, 13.6. HRMS (CI + NH3): m/z [M + H+] calcd for C22H25N2O5: 397.1263; found: 397.1774.
(3 R *,4 S *,5 S *)-Ethyl 2-Benzyl-4-(4-nitrophenyl)-5-(2-oxooxazolidin-3-yl)isoxazolidine-3-carboxylate (3,5- cis -4d): colorless oil. IR (neat): 1739, 1520, 1346, 1244, 1207 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.17-8.20 (m, 2 H), 7.31-7.43 (m, 7 H), 5.79 (d, J = 3.8 Hz, 1 H), 4.27-4.39 (m, 2 H), 4.31 (d, J = 13.6 Hz, 1 H), 4.20 (dd, J = 3.8, 8.3 Hz, 1 H), 4.06-4.19 (m, 2 H), 4.10 (d, J = 13.6 Hz, 1 H), 3.86-3.97 (m, 2 H), 3.63 (d, J = 8.3 Hz, 1 H), 1.21 (t, J = 7.1 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 168.3, 157.7, 147.5, 145.5, 135.0, 129.5, 128.6, 128.4, 127.9, 124.3, 7.9, 75.2, 62.5, 62.0, 61.4, 56.8, 41.5, 14.0. HRMS (CI + CH4): m/z [M + H+] calcd for C22H24N3O7: 422.1614; found: 422.1632.
(3 R *,4 R *,5 R* )-Ethyl 2-Benzyl-4-(4-nitrophenyl)-5-(2-oxooxazolidin-3-yl)isoxazolidine-3-carboxylate (3,5- trans -4d): colorless oil. IR (neat): 1745, 1520, 1348 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 8.17 (d, J = 8.8 Hz, 2 H), 7.63 (d, J = 8.8 Hz, 2 H), 7.30-7.42 (m, 5 H), 5.81 (br, 1 H), 4.40 (d, J = 14.1 Hz, 1 H), 4.32-4.36 (m, 2 H), 4.15 (dd, J = 4.5, 7.8 Hz, 1 H), 4.06 (d, J = 7.8 Hz, 1 H), 4.00 (d, J = 14.1 Hz, 1 H), 3.79-3.91 (m, 2 H), 3.56-3.67 (m, 2 H), 0.90 (t, J = 7.3 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 166.9, 156.9, 147.5, 144.2, 135.4, 129.8, 129.3, 128.3, 127.8, 123.7, 87.9, 70.0, 62.1, 61.1, 60.1, 53.1, 40.8, 13.7. HRMS (CI + CH4): m/z [M + H+] calcd for C22H24N3O7: 422.1614; found: 422.1641.
(3 R* ,4 S* ,5 S *)-Ethyl 2-Benzyl-4-(4-methoxyphenyl)-5-(2-oxooxazolidin-3-yl)isoxazolidine-3-carboxylate (3,5- cis -4e): colorless oil. IR (neat): 1736, 1514, 1246, 1179, 1031 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.27-7.38 (m, 5 H), 7.14-7.18 (m, 2 H), 6.84-6.87 (m, 2 H), 5.81 (d, J = 4.8 Hz, 1 H), 4.27-4.38 (m, 2 H), 4.21 (d, J = 13.9 Hz, 1 H), 4.10 (d, J = 13.9 Hz, 1 H), 4.00-4.12 (m, 2 H), 4.02 (dd, J = 4.8, 8.8 Hz, 1 H), 3.93-4.00 (m, 1 H), 3.86-4.92 (m, 1 H), 3.79 (s, 3 H), 3.61 (d, J = 8.8 Hz, 1 H), 1.18 (t, J = 7.1 Hz, 3 H). ¹³C NMR 100 MHz (CDCl3): δ = 169.0, 159.23, 159.20, 157.8, 135.6, 129.4, 128.6, 128.3, 127.7, 114.5, 88.3, 76.0, 62.4, 61.9, 61.6, 56.0, 55.3, 41.3, 14.0. HRMS (CI + NH3): m/z [M + H+] calcd for C23H27N2O6: 427.1869; found: 427.1885.
(3 R* ,4 S* ,5 S* )-Ethyl 2-Benzyl-4-(4-methoxyphenyl)-5-(2-oxooxazolidin-3-yl)isoxazolidine-3-carboxylate (3,5- trans -4e): colorless oil. IR (neat): 1738, 1194, 1028 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.28-7.41 (m, 7 H), 6.81-6.86 (m, 2 H), 5.90 (br, 1 H), 4.34 (d, J = 14.0 Hz, 1 H), 4.25-4.35 (m, 2 H), 3.98 (d, J = 14.0 Hz, 1 H), 3.95-3.98 (m, 2 H), 3.79-3.87 (m, 2 H), 3.77 (s, 3 H), 3.57-3.61 (m, 2 H), 0.90 (t, J = 7.1 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 167.6, 159.1, 157.10, 157.13, 135.7, 129.4, 128.6, 128.3, 127.7, 114.5, 88.0, 70.6, 62.0, 60.8, 60.2, 55.2, 50.2, 40.3, 13.7.
cis -3-(3-Benzoyl-2-benzylisoxazolidin-5-yl)oxazolidin-2-one (3,5- cis -3b): colorless crystal; mp 115 ˚C (Et2O). IR (neat): 1753, 1677, 1239, 1211, 1112 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.65-7.68 (m, 2 H), 7.52-7.56 (m, 1 H), 7.32-7.38 (m, 7 H), 6.14 (dd, J = 5.1, 8.6 Hz, 1 H), 4.57 (dd, J = 5.6, 8.8 Hz, 1 H), 4.29-4.33 (m, 2 H), 4.14 (d, J = 12.7 Hz, 1 H), 4.06 (d, J = 12.7 Hz, 1 H), 3.74-3.87 (m, 2 H), 2.89 (ddd, J = 8.6, 8.8, 13.6 Hz, 1 H), 2.74 (ddd, J = 5.1, 5.6, 13.6 Hz, 1 H). ¹³C NMR (100 MHz, CDCl3): δ = 195.7, 157.8, 135.7, 135.3, 133.5, 129.7, 128.7, 128.6, 128.5, 128.1, 82.9, 67.8, 62.5, 61.9, 40.4, 33.0.
trans -3-(3-Benzoyl-2-benzylisoxazolidin-5-yl)oxazolidin-2-one (3,5- trans -3b): colorless crystal; mp 194 ˚C (Et2O). IR (neat): 1742, 1693, 1418, 1263, 1218 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.86-7.88 (m, 2 H), 7.54-7.58 (m, 1 H), 7.38-7.42 (m, 2 H), 7.27-7.32 (m, 5 H), 5.86-5.89 (m, 1 H), 4.68-4.71 (m, 1 H), 4.34-4.38 (m, 2 H), 4.01-4.09 (m, 2 H), 3.68-3.72 (m, 2 H), 2.89-2.99 (m, 1 H), 2.81-2.90 (m, 1 H). ¹³C NMR (100 MHz, CDCl3): δ = 195.2, 156.8, 135.8, 135.2, 133.6, 129.5, 128.9, 128.6, 128.4, 17.8, 84.3, 68.5, 62.0, 61.2, 41.7, 33.2. HRMS (CI + NH3): m/z [M + H+] calcd for C20H21N2O4: 353.1501; found: 353.1485.
3-[(3 R* ,4 S *,5 S* )-3-Benzoyl-2-benzyl-4-phenylisoxazolidin-5-yl]oxazolidin-2-one (3,5- cis -4f): colorless crystal; mp 184 ˚C (Et2O). IR (neat): 1741, 1681, 1205 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.48-7.51 (m, 2 H), 7.37-7.41 (m, 3 H), 7.22-7.30 (m, 5 H), 7.00-7.09 (m, 5 H), 5.62 (d, J = 4.6 Hz, 1 H), 4.87 (d, J = 8.1 Hz, 1 H), 4.38 (d, J = 13.9 Hz, 1 H), 4.29 (dd, J = 4.7, 8.1 Hz, 1 H), 4.21-4.25 (m, 2 H), 3.93 (d, J = 13.9 Hz, 1 H), 3.63-3.69 (m, 1 H), 3.51-3.57 (m, 1 H). ¹³C NMR (100 MHz, CDCl3): δ = 194.7, 156.8, 136.7, 136.3, 136.1, 133.1, 129.4, 128.9, 128.4, 128.3, 128.2, 127.6, 127.5, 89.6, 72.8, 62.0, 60.6, 53.7, 42.4. HRMS (CI + NH3): m/z [M + H+] calcd for C26H25N2O4: 429.1814; found: 429.1843.
cis -Ethyl 2-Benzyl-4,4-dimethyl-5-(2-oxooxazolidin-3-yl)isoxazolidine-3-carboxylate (3,5- cis -4g): colorless oil. IR (neat): 1747, 1726, 1203 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.27-7.38 (m, 5 H), 5.33 (s, 1 H), 4.13-4.27 (m, 4 H), 4.11 (d, J = 13.6 Hz, 1 H), 3.79 (d, J = 13.6 Hz, 1 H), 3.73-3.79 (m, 1 H), 3.51-3.58 (m, 1 H), 3.27 (s, 1 H), 1.42 (s, 3 H), 1.29 (t, J = 7.3 Hz, 3 H), 1.05 (s, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 168.8, 158.5, 136.2, 129.4, 128.3, 127.7, 91.0, 77.7, 62.8, 61.6, 61.0, 51.4, 42.4, 28.7, 19.1, 14.3. HRMS (CI + NH3): m/z [M + H+] calcd for C18H25N2O5: 349.1763; found: 349.1767.
trans -Ethyl 2-Benzyl-4,4-dimethyl-5-(2-oxooxazolidin-3-yl)isoxazolidine-3-carboxylate (3,5- trans -4g): colorless crystal; mp 85 ˚C (Et2O). IR (neat): 1747, 1722, 1255, 1216 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.27-7.38 (m, 5 H), 5.35 (s, 1 H), 4.28-4.32 (m, 2 H), 4.29 (d, J = 13.9 Hz, 1 H), 4.15-4.27 (m, 2 H), 3.93 (d, J = 13.9 Hz, 1 H), 3.60-3.66 (m, 1 H), 3.40-3.46 (m, 1 H), 3.26 (s, 1 H), 1.30 (t, J = 7.0 Hz, 3 H), 1.26 (s, 3 H), 1.20 (s, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 167.9, 157.7, 135.5, 129.4, 128.2, 127.7, 90.8, 74.9, 62.3, 61.1, 60.5, 49.2, 41.5, 23.6, 21.3, 14.2. Anal. Calcd for C18H24N2O5 (348.17): C, 62.05; H, 6.94; N, 8.04. Found: C, 62.16; H, 7.06; N, 8.10.
cis -(3-Benzoyl-2-benzyl-4,4-dimethylisoxazolidin-5-yl)oxazolidin-2-one (3,5- cis -4h): pale yellow oil. IR (neat): 1733, 1688, 1226 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.27-7.38 (m, 10 H), 5.58 (s, 1 H), 4.49 (d, J = 14.7 Hz, 1 H), 4.25-4.33 (m, 2 H), 4.12 (s, 1 H), 3.93 (d, J = 14.7 Hz, 1 H), 3.62-3.69 (m, 1 H), 3.55-3.61 (m, 1 H), 0.90 (s, 3 H), 0.88 (s, 3 H).¹³C NMR (100 MHz, CDCl3): δ = 196.7, 158.7, 137.0, 136.0, 133.6, 129.2, 128.3, 127.6, 127.4, 127.3, 86.6, 84.3, 62.7, 56.8, 49.7, 42.6, 18.7, 18.4. HRMS (CI + NH3): m/z [M + H+] calcd for C22H25N2O4: 381.1814; found: 381.1833.
trans -(3-Benzoyl-2-benzyl-4,4-dimethylisoxazolidin-5-yl)oxazolidin-2-one (3,5- trans -4h): colorless crystal; mp 165-166 ˚C (Et2O). IR (neat): 1752, 1681, 1215 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 7.92-7.98 (m, 2 H), 7.57-7.65 (m, 1 H), 7.43-7.52 (m, 2 H), 7.28-7.33 (m, 5 H), 5.39 (s, 1 H), 4.29-4.37 (m, 2 H), 4.28 (d, J = 14.1 Hz, 1 H), 4.12 (s, 1 H), 3.93 (d, J = 14.1 Hz, 1 H), 3.65-3.78 (m, 1 H), 3.46-3.57 (m, 1 H), 1.18 (s, 3 H), 1.07 (s, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 195.9, 157.7, 137.3, 135.2, 133.7, 129.6, 128.8, 128.7, 128.2, 127.8, 91.3, 77.7, 62.4, 60.0, 49.6, 41.8, 24.2, 22.1.