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Synlett 2009(17): 2795-2800  
DOI: 10.1055/s-0029-1217961
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Gold(III) Chloride Catalyzed Intermolecular Dimerization of 2-Ethynylanilines: Synthesis of Substituted Quinolines

C. Praveen, S. Jegatheesan, P. T. Perumal*
Organic Chemistry Division, Central Leather Research Institute, Adyar, Chennai 600 020, India
Fax: +91(44)24911589; e-Mail: ptperumal@gmail.com;
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Publication History

Received 8 July 2009
Publication Date:
09 September 2009 (online)

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Abstract

An unprecedented gold(III)-catalyzed intermolecular dimerization of 2-ethynylanilines possessing terminal triple bond offers a general synthetic pathway to a wide range of highly substituted quinolines.

Key words

2-ethynylanilines - terminal alkyne - gold(III) - intermolecular dimerization - substituted quinolines

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Utilization of polar solvents like MeOH, EtOH, and wet MeCN resulted in the hydration of 2-ethynylaniline to form 2′-aminoacetophenone, and reaction in nonpolar solvents like CH2Cl2 and toluene led to the product formation only in 10% and 15% yield, respectively.

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General Procedure for the Gold-Catalyzed Dimerization of 2-Ethynylanilines 2a-o; Representative Procedure for 2,4-Dibromo-6-(6,8-dibromo-4-methyl-2-quinolinyl)-phenylamine (2l, Table 2, Entry 12)
To a mixture of AuCl3 (27.57 mg, 0.09 mmol) and AgOTf (46 mg, 0.181 mmol) under N2 was added dry MeCN (2 mL) and stirred for 15 min at 25 ˚C. To the mixture was added a solution of 2,4-dibromo-6-ethynylaniline (1l, 500 mg, 1.81 mmol) in dry MeCN (2 mL) at 25 ˚C, and the whole was gradually warmed up to reflux temperature and stirred for the specified time (Table  [²] ). After completion of the reaction as indicated by TLC, the reaction mixture was concentrated under reduced pressure and purified by column chromatog-raphy over silica gel (100-200 mesh) to afford pure product 2,4-dibromo-6-(6,8-dibromo-4-methyl-2-quinolinyl)phenyl-amine(2l) as a yellow solid; mp 186-188 ˚C. IR (KBr): 3751, 3473, 2956, 2430,1457, 766 cm-¹. ¹H NMR (500 MHz, CDCl3): δ = 2.51 (s, 3 H), 4.12 (br s, 2 H), 7.10 (d, 1 H, J = 2.3 Hz), 7.65 (d, 1 H, J = 2.2 Hz), 8.14 (d, 1 H, J = 2.3 Hz), 8.19 (d, 1 H, J = 2.3 Hz), 8.71 (s, 1 H). ¹³C NMR (125 MHz, CDCl3): δ = 26.9, 109.2, 110.1, 120.7, 124.7, 126.6, 126.7, 129.9, 131.4, 132.1, 134.9, 136.0, 141.6, 143.2, 152.1, 162.8. MS (ESI+): m/z = 551 [M+ + H]+, 553 [M²+ + H]+, 555 [M4+ + H]+. Anal. Calcd for C16H10Br4N2: C, 34.95; H, 1.83; N, 5.09. Found: C, 35.07; H, 1.78; N, 5.00.