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Synlett 2008(16): 2513-2517  
DOI: 10.1055/s-2008-1078178
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Silver(I) versus Gold(I) Catalysis in Benzannulation Reaction: A Versatile Access to Acridines

Thomas Godet, Philippe Belmont*
Laboratoire de Synthèse et Méthodologie Organiques, Institut de Chimie et Biochimie Moléculaires et Supramoléculaires (ICBMS), Université Lyon 1, CNRS, UMR 5246, Bâtiment CPE, 43 boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France
Fax: +33(4)72432963; e-Mail: philippe.belmont@univ-lyon1.fr;
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Publication History

Received 4 June 2008
Publication Date:
10 September 2008 (online)

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Abstract

A silver/gold-catalysed benzannulation reaction is described. In the presence of catalytic amounts of gold and/or silver salts, the reaction of silyl enol ethers onto alkynes occurs under mild conditions to produce the corresponding polycyclic aromatic systems (acridine, quinoline or naphthalene cores) in good to high yields. Among the catalysts investigated, AgOTf has been chosen as a general catalyst for this reaction which likely proceeds through silver(I) activation of the alkynyl moiety leading to a subsequent cycloisomerisation reaction.

Key words

silver - gold - benzannulation - acridine - quinoline

22

See ref. 18.

34

To our knowledge the only related example can be found in the work of Dankwardt, where he used AuCl3 (10 mol%) in toluene at 100 ˚C (Scheme  [5] ). See ref. 15.

37

In ref. 15, Dankwardt reported the use of 1.1 equivalents of AgCO2CF3 in nitromethane at r.t.

43

Typical Procedure: To a flask charged with silyl enol ether quinoline (0.1 mmol) [44] dissolved in anhyd 1,2-dichloro-ethane (10 mL), was added silver catalyst (5 mol%). The reaction mixture was stirred at 50 ˚C until the reaction was judged complete by TLC analysis (0.5-2 h). The crude mixture was dissolved in CH2Cl2 and washed with a sat. aq solution of NaHCO3 (3 ×). The organic phase was dried over Na2SO4, filtered and the solvents were removed in vacuo. If needed, the residue was loaded on a silica gel column and elution with the appropriate mixture of cyclohexane and EtOAc yielded the pure cyclised products.
Selected spectroscopic data for entry 8, Table  [³] : isolated as a yellow oil (97%). ¹H NMR (300 MHz, CDCl3, 25 ˚C): δ = 9.04 (s, 1 H), 8.20 (app d, ³ J H,H = 8.8 Hz, 1 H), 8.02 (app d, ³ J H,H = 8.3 Hz, 1 H), 7.77 (s, 1 H), 7.77 (ddd, ³ J H,H = 8.7, 6.7 Hz, 4 J H,H = 1.4 Hz, 1 H), 7.51 (ddd, ³ J H,H = 8.0, 6.6 Hz, 4 J H,H = 0.8 Hz, 1 H), 7.43-7.45 (m, 2 H), 7.34 (t, ³ J H,H = 7.0 Hz, 2 H), 7.26 (m, 1 H), 7.03 (d, 4 J H,H = 1.0 Hz, 1 H), 3.69 (s, 2 H), 3.63 (s, 2 H), 2.26 (s, 3 H), 1.15 (s, 9 H), 0.37 (s, 6 H). ¹³C NMR (75 MHz, CDCl3, 25 ˚C): δ = 151.6, 150.2, 149.2, 143.2, 139.6, 131.8, 130.5, 129.2, 128.9, 128.9, 128.4, 127.1, 126.0, 125.3, 122.3, 121.3, 111.7, 62.2, 62.2, 42.6, 26.1, 18.7, -4.1. MS (ESI+): m/z (%) = 443 (100) [M + H] + . HRMS (CI): m/z calcd for C28H35N2OSi+: 443.2519; found: 443.2522.

44

Silyl enol ether quinolines (Table  [³] ) were prepared following a published procedure. Please see ref. 33.