Synlett 2004(9): 1553-1556  
DOI: 10.1055/s-2004-829088
LETTER
© Georg Thieme Verlag Stuttgart · New York

Methyltrioxorhenium-Catalyzed Oxidation of Aromatic Aldoximes

Francesca Cardona*a, Gianluca Soldainia, Andrea Goti*a,b
a Dipartimento di Chimica Organica ‘Ugo Schiff’, Università di Firenze, via della Lastruccia 13, Sesto Fiorentino, Firenze 50019, Italy
b Associated with ICCOM-CNR, Firenze, Italy
Fax: +39(055)4573531; e-Mail: andrea.goti@unifi.it;
Further Information

Publication History

Received 11 January 2004
Publication Date:
29 June 2004 (online)

Abstract

The first catalytic oxidation of aryl oximes to nitro compounds by means of methyltrioxorhenium and urea hydroperoxide is reported. The formation of carbamates, probably occurring through formation of nitrile oxide intermediates, has been observed from 2,6-disubstituted aryl oximes.

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Typical Procedure for the Oxidation of Oximes: A 10 mL reaction flask was charged sequentially with MTO (0.02-0.04 mmol), MeOH (2 mL), and UHP (3 mmol). The stirred solution became yellow due to the formation of peroxy species and after 5 min the oxime (1 mmol) was added. The reaction mixture was stirred at r.t. for the time reported in Table [1] . The solvent was evaporated, the crude reaction mixture was added with CH2Cl2 and the undissolved urea was filtered off. The pure products were collected by chromatography on silica gel using the appropriate eluent.

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All new compounds gave satisfactory analytical and spectroscopic data.

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Selected data for carbamates:
8: Rf = 0.17 (petroleum ether-Et2O 6:1). Pale yellow solid; mp 118-120 °C. IR (CDCl3): 3421, 2984, 2934, 1730, 1497, 1227 cm-1. 1H NMR (200 MHz, CDCl3): δ = 7.39-7.34 (m, 2 H, ArH), 7.20-7.11 (m, 1 H, ArH), 6.26 (br s, 1 H, NH), 4.24 (q, 2 H, J = 7.0 Hz, OCH2), 1.30 (t, 3 H, J = 7.0 Hz, CH2CH3). 13C NMR (50 MHz, CDCl3): δ = 153.8, 133.8, 132.0, 128.4, 128.2, 62.0, 14.4. MS: m/z (%) = 233 (4) [M+ - 1], 200(13), 198 (47), 176 (32), 173 (40), 163 (54), 161 (100). Anal. Calcd for C9H9Cl2NO2: C, 46.18; H, 3.88; N, 5.98. Found: C, 46.48; H, 3.84; N, 5.76.
11: Rf = 0.20 (petroleum ether-Et2O 4:1). White solid; mp 107-109 °C. IR (CDCl3): 3427, 3314, 2956, 2922, 2861, 1726, 1500, 1450, 1355, 1225 cm-1. 1H NMR (200 MHz, CDCl3): δ = 6.90 (m, 2 H, ArH), 6.11 (br s, 1 H, NH), 3.76 (br s, 3 H, OCH3), 2.28 (s, 3 H), 2.22 (s, 6 H). 13C NMR (50 MHz, CDCl3): δ = 155.1, 136.8, 135.6, 130.9, 128.8, 52.4, 20.8, 18.1. MS: m/z (%) = 193 (91) [M+], 162 (34), 160 (45), 146 (27), 135 (80), 132 (100), 119 (23), 91 (51). Anal. Calcd for C11H15NO2: C, 68.37; H, 7.82; N, 7.25. Found: C, 68.76; H, 7.85; N, 7.72.

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Selected data for cycloadducts:
16: White solid; mp 207-209 °C (CH3OH). IR (CDCl3): 3072, 2975, 1732, 1562, 1499, 1433, 1377, 1192 cm-1. 1H NMR (200 MHz, CDCl3): δ = 7.48-7.26 (m, 8 H, ArH), 5.73 (d, 1 H, J = 9.3 Hz, H-6a), 4.91 (d, 1 H, J = 9.3 Hz, H-3a). 13C NMR (50 MHz, CDCl3): δ = 171.1, 168.9, 150.0, 135.2, 132.1, 130.8, 129.4, 129.2, 128.4, 126.0, 125.3, 80.0, 56.7. MS: m/z (%) = 361 (10) [M+], 360 (27) [M+ - 1], 212 (51), 173 (50), 119 (100), 91 (7). Anal. Calcd for C17H10Cl2N2O3: C, 56.53; H, 2.79; N, 7.76. Found: C, 56.37; H, 2.64; N, 8.00.
19: Rf = 0.19 (petroleum ether-Et2O 5:1). White solid; mp 129-130 °C. IR (CDCl3): 2956, 1743, 1437, 1310, 1269, 1225 cm-1. 1H NMR (200 MHz, CDCl3): δ = 6.87 (m, 2 H, ArH), 5.58 (d, 1 H, J = 6.6 Hz, H-5), 4.70 (d, 1 H, J = 6.6 Hz, H-4), 3.85 (s, 3 H, OCH3), 3.60 (s, 3 H, OCH3), 2.27 (s, 3 H), 2.18 (s, 6 H). 13C NMR (50 MHz, CDCl3): δ = 169.3, 167.2, 153.5, 139.2, 136.9, 128.5, 123.3, 80.7, 59.7, 53.1, 53.0, 21.1, 19.6. MS: m/z (%) = 306 (1) [M+], 305 (5) [M+ - 1], 246 (32), 219 (25), 214 (10), 186 (61), 158 (29), 57 (100). Anal. Calcd for C16H19NO5: C, 62.94; H, 6.27; N, 4.59. Found: C, 62.58; H, 6.02; N, 4.40.

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Typical Procedure for the Synthesis of Cycloadducts: To a stirred solution of MTO (0.04 mmol) in MeOH (2 mL) was added UHP (3 mmol), the dipolarophile (1.5 mmol) and the oxime (1 mmol). The reaction mixture was stirred at r.t. until no more oxime was detected by TLC. The solvent was evaporated, the crude mixture was added with CH2Cl2 and the undissolved urea was filtered off. The residue was purified by chromatography on silica gel to afford the pure products.