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Synlett 2007(19): 2965-2968  
DOI: 10.1055/s-2007-990971
LETTER
© Georg Thieme Verlag Stuttgart · New York

Regioselective Synthesis of New 1-Aminopyrroles and 1-Amino-4,5,6,7-tetrahydroindoles by One-Pot ‘Conjugate Addition/Cyclization’ Reactions of 1,3-Bis(silyl enol ethers) with 1,2-Diaza-1,3-butadienes

Andreas Schmidta, Vahuni Karapetyana,b, Orazio A. Attanasic, Gianfranco Favic, Helmar Görlsd, Fabio Mantellinic, Peter Langer*a,e
a Institut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany
b Faculty of Chemistry, Yerevan State University, Alex Manoogian 1, 0025 Yerevan, Armenia
c Istituto di Chimica Organica, Università degli Studi di Urbino ‘Carlo Bo’, Via I Maggetti 24, 61029 Urbino, Italy
d Institut für Anorganische und Analytische Chemie, Universität Jena, August-Bebel-Str. 2, 07740 Jena, Germany
e Leibniz-Institut für Katalyse e.V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany
e-Mail: peter.langer@uni-rostock.de;
Further Information

Publication History

Received 19 July 2007
Publication Date:
08 November 2007 (online)

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Abstract

Unknown functionalized 1-aminopyrroles and 1-amino-4,5,6,7-tetrahydroindoles were prepared under mild conditions and with excellent yields by one-pot ‘conjugate addition/cyclization’ reactions of 1,3-bis(silyl enol ethers) with 1,2-diaza-1,3-butadienes.

Key words

cyclizations - 1,2-diaza-1,3-butadienes - N-heterocycles - pyrroles - silyl enol ethers

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General Procedure for the Synthesis of 3 and 5: To a CH2Cl2 solution (12 mL) of 1,2-diaza-1,3-butadiene 1 (2.0 mmol) was added 1,3-bis(silyl enol ether) 2 or 4 (2.4 mmol) and freshly dried ZnCl2 (0.055 g, 0.4 mmol) at 20 °C. The solution was stirred for 12 h at r.t. and subsequently TFA (0.3 mL) was added. The solvent was removed in vacuo and the residue was purified by column chromatography [silica gel, heptane → heptane-EtOAc (30:70)].
Synthesis of 3d: Prepared from 1,2-diaza-1,3-butadiene 1a (0.370 g, 2.0 mmol), 1-tert-butoxy-1,3-bistrimethylsilyl-oxybuta-1,3-diene (2d; 0.726 g, 2.4 mmol) and ZnCl2 (0.055 g, 0.4 mmol). Compound 3d was purified by chromatog-raphy and crystallized (EtOH) as a colorless solid (0.527 g, 81%); mp 178-180 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 1.25 (t, 3 J = 7.1 Hz, 3 H, CH2CH 3), 1.42 (s, 9 H, t-Bu), 2.29 (s, 3 H, CMe), 3.34 (dd, 2 J = 17.0 Hz, 1 H, CCH2), 3.44 (dd, 2 J = 17.0 Hz, 1 H, CCH2), 4.16 (q, 3 J = 7.1 Hz, 2 H, CH 2CH3), 6.19 (br, 2 H, CONH2), 6.23 (s, 1 H, HHetar), 9.06 (s, 1 H, NNHCO). 13C NMR (62.9 MHz, DMSO-d 6): δ = 10.5 (CH2 CH3), 14.6 (NCCH3), 27.9 [C(CH3)3], 32.2 (CCH2CO), 58.9 (OCH2), 80.6 [OC(CH3)3], 106.2 (CHHetar), 108.7 (CCOO), 126.5, 136.6 (NCHetar), 157.2, 164.4, 169.1 (CO). IR (KBr): 3405 (s), 3270 (m), 2981 (m), 2934 (w), 2907 (w), 1740 (s), 1675 (s), 1576 (m), 1531 (m), 1477 (m), 1457 (m), 1414 (m), 1388 (m), 1371 (m), 1352 (m), 1229 (s), 1146 (s), 1081 (s), 1021 (w), 849 (w), 773 (w), 627 (w), 602 (w), 483 (w) cm-1. MS (EI, 70 eV): m/z (%) = 325 (11) [M+], 269 (18), 224 (100), 207 (26), 166 (27), 57 (79). HRMS (EI, 70 eV): m/z [M]+ calcd for C15H23N3O5: 325.16322; found: 325.162992.

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CCDC 653476 contains all crystallographic details of this publication and is available free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html or can be ordered from the following address: Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: +44(1223)336033; or deposit@ccdc.cam.ac.uk.