Synlett 2006(1): 0106-0108  
DOI: 10.1055/s-2005-922759
LETTER
© Georg Thieme Verlag Stuttgart · New York

Access to Eight-Membered Ring Lactams from Five-Membered Ring 1,4-Diketones and Primary Amines

Michael Rössle, Jens Christoffers*
Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
Fax: +49(711)6854269; e-Mail: jchr@oc.uni-stuttgart.de;
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Publikationsverlauf

Received 10 October 2005
Publikationsdatum:
16. Dezember 2005 (online)

Abstract

Unsaturated eight-membered ring lactams are obtained by expansion of the five-membered ring of a 1,4-diketone with primary amines. Azabicyclo[3.3.0]octanes are the proposed reaction intermediates; there has been a single azabicyclo[3.3.0]octane isolated. Reaction of the 1,4-diketone with phenylhydrazine yields a new cyclopenta[c]pyridazine.

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Ethyl 1-Butyl-8-oxo-2-phenyl-1,4,5,6,7,8-hexahydro-azocine-4-carboxylate ( 2c): A suspension of ester 1 (100 mg, 365 µmol), n-BuNH2 (133 mg, 1.83 mmol, 5 equiv), and Bi(NO3)3·5H2O (9 mg, 18 µmol, 0.05 equiv) in THF (1.0 mL) was stirred in a closed reaction vial for 2 d at 70 °C. After cooling to ambient temperature, the reaction mixture was chromatographed (basic alumina; hexanes-EtOAc, 2:1) to give lactam 2c (74 mg, 223 µmol, 61%) as a yellowish oil; R f (silica) 0.32. IR (ATR): 2956 (m), 2931 (s), 2862 (m), 1733 (vs), 1654 (vs), 1446 (s), 1399 (s), 1179 (s) cm-1. 1H NMR (CDCl3, 500 MHz): δ = 0.83 (t, J = 7.4 Hz, 3 H), 1.19-1.26 (m, 2 H), 1.30 (t, J = 7.1 Hz, 3 H), 1.33-1.37 (m, 1 H), 1.41-1.55 (m, 1 H), 1.75-1.85 (m, 1 H), 1.99-2.04 (m, 1 H), 2.13-2.18 (m, 2 H), 2.44 (dt, J = 1.4 Hz, J = 12.3 Hz, 1 H), 2.51 (ddd, J = 1.4 Hz, J = 8.0 Hz, J = 11.9 Hz, 1 H), 2.65 (ddd, J = 5.0 Hz, J = 10.0 Hz, J = 13.6 Hz, 1 H), 3.04 (ddd, J = 0.9 Hz, J = 10.2 Hz, J = 10.6 Hz, 1 H), 4.09 (ddd, J = 6.0 Hz, J = 9.9 Hz, J = 13.4 Hz, 1 H), 4.21 (q, J = 7.1 Hz, 2 H), 6.02 (d, J = 9.9 Hz, 1 H), 7.36-7.38 (m, 5 H) ppm. 13C NMR (CDCl3, 125 MHz): δ = 13.79 (CH3), 14.20 (CH3), 20.31 (CH2), 24.13 (CH2), 29.39 (CH2), 29.60 (CH2), 33.59 (CH2), 43.79 (CH), 44.65 (CH2), 61.03 (CH2), 124.34 (CH), 126.28 (2 × CH), 128.84 (2 × CH), 128.94 (CH), 135.73 (C), 140.44 (C), 173.85 (C), 173.87 (C) ppm. MS (70 eV, EI): m/z (%) = 329 (100) [M+]. Anal. Calcd for C20H27NO3: C, 72.92; H, 8.26; N, 4.25. Found: C, 73.07; H, 8.35; N, 4.31.

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Ethyl 4,5,6,6a-Tetrahydro-6a-hydroxy-2-phenyl-3 H -cyclopenta[ b ]pyrrole-3a-carboxylate ( 3): A mixture of ester 1 (56 mg, 0.20 mmol), molecular sieves (4 Å, ca. 90 mg) and liquid NH3 (ca. 4 mL) was stirred for 7 h at -75 °C. After evaporation of the solvent upon warming to ambient temperature the residue was suspended in CHCl3 (ca. 2 mL), filtered, the solvent again evaporated, and the residue chromatographed (silica; hexanes-EtOAc-Et3N, 8.3:1.7:1) to give 3 (35 mg, 0.13 mmol, 63%) as light brown crystals. Mp 142 °C; R f (silica; hexanes-EtOAc, 2:1) 0.18. IR (ATR): 3066 (br, m), 2962 (m), 2929 (m), 2799 (m), 1724 (vs), 1627 (s), 1577 (m), 1450 (m), 1362 (m), 1345 (m), 1322 (m), 1298 (s), 1284 (s), 1235 (m), 1184 (s), 1146 (s), 1125 (s), 1087 (s), 1023 (m), 942 (w) cm-1. 1H NMR (500 MHz, CDCl3): δ = 1.30 (t, J = 7.1 Hz, 3 H), 1.32-1.42 (m, 1 H), 1.73 (ddt, J = 13.1 Hz, J = 6.2 Hz, J = 2.0 Hz, 1 H), 1.77-1.84 (m, 1 H), 2.05 (dt, J = 12.5 Hz, J = 6.6 Hz, 1 H), 2.26 (ddt, J = 12.9 Hz, J = 6.0 Hz, J = 2.0 Hz, 1 H), 2.66 (dt, J = 12.3 Hz, J = 6.6 Hz, 1 H), 2.89 (d, J = 18.0 Hz, 1 H, CHH), 4.02 (d, J = 18.0 Hz, 1 H, CHH), 4.07 (s, br, 1 H, OH), 4.19-4.26 (m, 2 H), 7.40-7.44 (m, 2 H), 7.46-7.50 (m, 1 H), 7.85-7.89 (m, 2 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 14.26 (CH3), 22.85 (CH2), 37.47 (CH2), 39.96 (CH2), 48.13 (CH2), 58.92 (C), 61.29 (CH2), 116.03 (C), 128.24 (2 × CH), 128.52 (2 × CH), 131.37 (CH), 133.21 (C), 171.99 (C), 174.25 (C) ppm. MS (EI, 70 eV): m/z (%) = 273 (78) [M+], 244 (30) [M+ - Et], 231 (36), 200 (100) [M+ - CO2Et]. Anal. Calcd C16H19NO3: C, 70.36; H, 7.01; N, 5.13. Found: C, 70.05; H, 7.07; N, 4.99.

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Ethyl 1-(Benzoylmethyl)-2-phenylhydrazonocyclo-pentane-1-carboxylate ( 5): A solution of ester 1 (400 mg, 1.46 mmol) in EtOH (2.0 mL) was added to a mixture of phenylhydrazine (176 mg, 1.63 mmol, 1.1 equiv), AcOH (0.68 mL), and EtOH (4.0 mL). After stirring for 30 min at 23 °C the mixture was poured onto ice and H2O (ca. 25 g). After filtration the residue was dried in vacuo to give a yellow solid (500 mg, 1.37 mmol, 94%). Mp 106 °C. IR (ATR): 3320 (m), 2968 (m), 1700(vs), 1685 (vs), 598 (vs), 1494 (m), 1229 (vs), 1180 (s), 1128 (s) cm-1. 1H NMR (CDCl3, 500 MHz): δ = 1.20 (t, J = 7.1 Hz, 3 H), 1.83 (ddd, J = 7.7 Hz, J = 9.8 Hz, J = 13.1 Hz, 1 H), 1.94-2.00 (m, 1 H), 2.16-2.25 (m, 1 H), 2.35-2.42 (m, 1 H), 2.48 (ddd, J = 3.9 Hz, J = 9.4 Hz, J = 17.2 Hz, 1 H), 2.77 (ddd, J = 3.4 Hz, J = 7.3 Hz, J = 13.0 Hz, 1 H), 3.23 (d, J = 18.1 Hz, 1 H), 4.11 (d, J = 18.1 Hz, 1 H), 4.16 (q, J = 7.0 Hz, 2 H), 6.80-6.83 (m, 1 H), 6.98-7.01 (m, 2 H), 7.17-7.21 (m, 2 H), 7.36 (s, 1 H), 7.44-7.48 (m, 2 H), 7.54-7.57 (m, 1 H), 7.98-8.00 (m, 2 H) ppm. 13C NMR (CDCl3, 125 MHz): δ = 14.08 (CH3), 22.46 (CH2), 26.25 (CH2), 35.60 (CH2), 45.69 (CH2), 54.44 (C), 61.00 (CH2), 112.90 (2 × CH), 119.92 (CH), 128.06 (2 × CH), 128.54 (2 × CH), 129.11 (2 × CH), 133.03 (CH), 137.09 (C), 145.36 (C), 153.46 (C), 173.27 (C), 197.97 (C) ppm. MS (EI, 70 eV): m/z calcd for C22H24N2O3 [M+], 364.1787; found, 364.1788.

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Ethyl 2,3-Diphenyl-2,5,6,7-tetrahydrocyclo-penta[ c ]pyridazine-4a-carboxylate ( 6): TFA (1 drop, ca. 10 mg) was added to a suspension of hydrazone 5 (60 mg, 0.16 mmol) and MgSO4 (150 mg) in CH2Cl2 (2.0 mL). After stirring the mixture for 4 h at 23 °C all volatile materials were removed in vacuo and the residue chromatographed (basic alumina; hexanes-EtOAc, 10:1) to give pyridazine 6 (30 mg, 87 µmol, 54%) as a yellow oil. R f (silica; hexanes-EtOAc, 2:1) 0.64. IR (ATR): 2976 (m), 1719 (vs), 1597 (s), 1495 (m), 1355 (m), 1221 (s), 1026 (m) cm-1. 1H NMR (CDCl3, 500 MHz): δ = 1.14 (t, J = 7.1 Hz, 3 H), 1.78-1.86 (m, 1 H), 1.93-2.06 (m, 2 H), 2.64-2.71 (m, 2 H), 2.89 (ddd, J = 6.5 Hz, J = 9.0 Hz, J = 16.8 Hz, 1 H), 4.05-4.12 (m, 2 H), 4.79 (s, 1 H), 6.85-6.89 (m, 1 H), 7.03-7.05 (m, 2 H), 7.07-7.11 (m, 2 H), 7.18-7.23 (m, 5 H) ppm. 13C NMR (CDCl3, 125 MHz): δ = 14.05 (CH3), 22.50 (CH2), 30.17 (CH2), 37.06 (CH2), 51.05 (C), 61.17 (CH2), 101.22 (CH), 121.16 (2 × CH), 122.55 (CH), 127.99 (3 × CH), 128.20 (2 × CH), 128.69 (2 × CH), 135.51 (C), 140.38 (C), 143.52 (C), 153.38 (C), 172.89 (C) ppm. MS (CI, CH4): m/z calcd for C22H23N2O2 [M + H+], 347.1759; found, 347.1766.