PDF icon Download PDF
Synlett 2005(11): 1758-1760  
DOI: 10.1055/s-2005-871568
LETTER
© Georg Thieme Verlag Stuttgart · New York

Cobalt-Mediated Regioselective Synthesis of Substituted Tetrahydroquinolines [1]

Ulrich Groth*, Thomas Huhn, Christian Kesenheimer, Aris Kalogerakis
Fachbereich Chemie, Universität Konstanz, Fach M-720, Universitätsstr. 10, 78457 Konstanz, Germany
Fax: +49(7531)884155; e-Mail: Ulrich.Groth@uni-konstanz.de;
Further Information

Publication History

Received 15 April 2005
Publication Date:
28 June 2005 (online)

   Permissions and Reprints All articles of this category
Preview

Abstract

A regioselective synthesis of polycyclic substituted ­pyridines is reported. Key step is the cobalt-catalyzed intramole­cular cyclization of diynenitriles, tethered by a silicon oxygen bond. Subsequent opening of the Si-O ring led then to the related tetra­hydroquinolines.

Key words

cobalt - catalysis - cycloaddition - pyridines - quinolines - ergot alkaloids

1

Transition Metal-Catalyzed Reactions in Organic Synthesis, X. For part IX, see: Fischer, S.; Groth, U.; Jung, M.; Lindenmaier, M.; Vogel, T. Tetrahedron Lett. 2005, in print.

1

Transition Metal-Catalyzed Reactions in Organic Synthesis, X. For part IX, see: Fischer, S.; Groth, U.; Jung, M.; Lindenmaier, M.; Vogel, T. Tetrahedron Lett. 2005, in print.

9

General Experimental Procedure.
a) To a solution of the diynenitrile 4 in Et2O were added 2.5 mol% CpCo(C2H4)2 at -80 °C. The resulting mixture was warmed to r.t. under stirring over 18 h. The organic phase was then concentrated in vacuum. Chromatography on silica gel provided pure pyridine 5.
b) A solution of 2.5 mol% CpCo(CO)2 in 2 mL toluene was added via cannula to a solution of the diynenitrile 4 in toluene and the mixture was heated at reflux under irradiation with a tungsten-lamp (Osram Vitalux 300 W) for 4 h. The organic phase was then concentrated in vacuum. Chromatography on silica gel provided pure pyridine 5.
Analytical data of selected compounds.
Compound 5a: R f = 0.21 (Et2O). Mp 44 °C. IR (film): 3010 (arom. H), 1570, 1550 (C=C, C=N) cm-1. 1H NMR (200 MHz, CDCl3): δ = 0.39 [s, 6 H, Si(CH3)2], 1.76-1.98 (m, 4 H, CH2), 2.75 (t, J = 11.5 Hz, 2 H, H-9), 2.92 (t, J = 11.5 Hz, 2 H, H-6), 5.09 (s, 2 H, OCH2), 8.25 (s, 1 H, arom. H). 13C NMR (50 MHz, CDCl3): δ = -0.12 [(Si(CH3)2], 22.70, 23.00, (C-7, C-8), 29.58 (C-6), 32.08 (C-9), 69.33 (C-3), 134.49 (C-9b), 140.34 (C-4), 141.85 (C-9a), 144.72 (C-3a), 154.12 (C-5a). MS (EI, 70 eV): m/z (%) = 219 (60) [M+], 43 (100) [C2H5N+]. Anal. Calcd for C12H17NOSi (219.3): C, 65.71; H, 7.81. Found: C, 65.72; H, 7.79.
Compound 13: R f = 0.55 (Et2O-CHCl3, 20:1). Mp 89 °C. IR (film): 3060 (arom. H), 2210 (C-N), 1600 (C=N) cm-1. 1H NMR (500 MHz, CDCl3): δ = 0.59 [s, 6 H, Si(CH3)2], 1.11 {d, J = 7 Hz, 18 H, Si[CH(CH3)2]3}, 1.64 {sp, J = 7 Hz, 18 H, Si[CH(CH3)2]3}, 4.56 (s, 2 H, H-3), 5.14 (s, 2 H, OCH2), 6.99 (s, 1 H, H-11), 7.10 (d, J = 7 Hz, 1 H, H-9), 7.12 (s, 1 H, H-2), 7.30 (dd, J 1 = J 2 = 7 Hz, 1 H, H-10), 8.20 (s, 1 H, H-5). 13C NMR (125 MHz, CDCl3): δ = 0.63 [Si(CH3)2], 12.67 {Si[CH(CH3)2]3), 18.06 {Si[CH(CH3)2]3}, 31.78 (C-3), 68.94 (OCH2), 112.88 (C-2a), 114.07, 114.13, 122.40 (C-9, C-10, C-11), 124.98 (C-2), 126.94 (C-8c), 129.68 (C-11b), 132.20 (C-8b), 139.39 (C-11a), 140.27 (C-8a), 141.35 (C-5), 143.15 (C-5a), 154.06 (C-3a). MS (EI, 70 eV): m/z (%) = 448 (100) [M+], 405 (55) [M+ - C3H7]. Anal. Calcd for C26H36N2OSi2 (448.8): C, 69.59; H, 8.09. Found: C, 69.48; H, 7.96.