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Synlett 2003(10): 1403-1406
DOI: 10.1055/s-2003-40833
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Intermolecular Alkyl Radical Addition to Methyl 2-(2,6-Dichlorophenyl)-2H-azirine-3-carboxylate

M. José Alvesb, Gil Fortesb, Emanuel Guimarãesa, Américo Lemos*a
a Departamento de Química e Bioquímica, Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, 8000-117 Faro, Portugal
Fax: +351(289)819403; e-Mail: alemos@ualg.pt;
b Escola de Ciências, Departamento de Química, Universidade do Minho, Campus Gualtar, 4710-057 Braga, Portugal
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Publication History

Received 15 May 2003
Publication Date:
24 July 2003 (online)

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Abstract

The 2H-azirine 1 acts as an effective radical acceptor for secondary and tertiary alkyl iodides mediated by triethylborane. The addition proceeds with high regio- and diastereo-selectivity.

Key words - 2H-azirine - intermolecular radical addition - triethyl­borane

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CCDC 207633 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax:+44(1223)336033; e-mail: deposit@ccdc.cam.ac.uk.).

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Typical Procedure: A solution of triethylborane (15% in hexane) (0.4 mL, 6.12 mmol) was added to a mixture of methyl 2-(2,6-dichlorophenyl)-2H-azirine-3-carboxylate (0.3g, 1.23 mmol) and the alkyl iodide (12.4 mmol) in CH2Cl2 (20 mL) at -40 °C. The reaction was maintained at this temperature for 30 min and the mixture was then washed with a 10% aq solution of NaHCO3 the organic layer dried (Na2SO4) and evaporated. Flash chromatography (hexanes/EtOAc: 80/20) afforded the product.
With iodoethane: Methyl 3-(2,6-dichlorophenyl)-2-ethylaziridine-2-carboxylate 2a, 0.24 g (71%), mp 53.0-54.5 °C (from toluene/CH2Cl2). (Found: C, 52.28; H, 4,92; N, 5,07. C12H13Cl2NO2 requires C, 52.57; H, 4.78; N, 5.11%). IR νmax = 1724, 1433, 1207, 777 cm-1. 1H NMR (300 ΜΗz): δ = 1.11 (3 H, t, J = 7.5 Hz), 1.52-1.64 (1 H, m, CH3HCH), 2.41-2.53 (2 H, m, CH3HCH and NH, integration became one after D2O shake), 3.12 (1 H, br s, H-3, turns into a sharp singlet after D2O shake), 3.57 (3 H, s,) 7.12-7.17 (1 H, m), 7.27-7.29 (2 H, m). MS (CI): m/z (%) = 274 (100), 276 (66), 278 (12) [(M + H)+].
With 2-iodopropane: Methyl 3-(2,6-dichlorophenyl)-2-(1-methylethyl) aziridine-2-carboxylate 2b, 0.29 g (82%); mp 81.7-82.9 (from hexanes/EtOAc). (Found: C, 53.96; H, 5.47; N, 5.03; C13H15Cl2NO2 requires C, 54.18; H, 5.25; N, 4.86%). IR νmax = 3209, 2968, 1724, 1433, 1207, 775 cm-1. 1H NMR (300 Μz): δ = 1.2 (9 H, s), 2.66 (1 H, br d, J = 7.3 Hz, aziridine NH), 3.28 (1 H, br d, J = 7.1 Hz, H-3), 3.47 (3 H, s) 7.10-7.16 (1 H, m), 7.25-7.28 (2 H, m). MS (CI): m/z (%) = 288 (100), 290 (66), 292 (12) [(M + H)+].
With 2-iodo-2-methylpropane: Methyl 3-(2,6-dichloro-phenyl)-2-(1,1-dimethylethyl)aziridine-2-carboxy-late 2c (0.33 g, 89%), as a low melting point solid. IR νmax = 3406, 2959, 1714, 1431, 1242, 774 cm-1. 1H NMR (300 Μz): δ = 1.2 (9 H, s), 2.66 (1 H, bd, J = 7.3 Hz, aziridine NH), 3.28 (1 H, bd, J = 7.1 Hz, H-3), 3.47 (3 H, s) 7.10-7.16 (1 H, m), 7.25-7.28 (2 H, m).
With iodocyclohexane: Methyl 3-(2,6-dichlorophenyl)-2-cyclohexylaziridine-2-carboxylate 2d, (0.32 g, 79%), mp 105.6-107.2 °C (from toluene/CH2Cl2), IR νmax = 3209, 2967, 1724, 1433, 1207, 775 cm-1. 1H NMR (300 Μz): δ = 1.08-1.9 (10 H, multiplet), 2.29 (1 H, br t, J = 4.2 Hz), 2.54 (1 H, br s, NH), 3.28 (1 H, br s), 7.10-7.16 (1 H, m), 7.26-7.29 (2 H, m).

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Similar mechanisms, for borane mediated reactions, have been proposed, see references: 1a) p. 5488; 2c); 2i); 2j); 5) p. 3429; 9) p. 86.