Cationic Au(I)-Catalyzed Cycloisomerization of Aromatic Enynes for the Synthesis of Substituted Naphthalenes
Takanori Shibata*, Yasunori Ueno, Kazumasa Kanda Department of Chemistry, School of Science and Engineering, Waseda University, Shinjuku, Tokyo, 169-8555, Japan e-Mail: tshibata@waseda.jp;
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Received
10 November 2005 Publication Date: 06 February 2006 (online)
A cationic Au(I) complex catalyzed the cycloisomerization of aromatic enynes that possess a substituent on their alkyne terminus. Cyclization of the 6-endo-dig type proceeded dominantly to give 1,3-di- and 1,2,3-trisubstituted naphthalenes.
Using AuCl3 (1 mol%) as a catalyst in toluene (see ref. 4), the cycloisomerization of 1a did not proceed at r.t. and it did at 100 °C for 24 h to give 2a yet in ca. 30% yield. Moreover, AuCl(PPh3) is more stable and easy to handle than hygroscopic AuCl3.
Typical Experimental Procedure (Table 2). AuCl(PPh3) (1.2 mg, 0.0024 mmol) was placed in a flask and a CH2Cl2 solution (2.5 mL) of aromatic enyne (0.25 mmol) was added. To the resulting mixture was added AgOTf (0.8 mg, 0.0030 mmol) and the mixture was stirred at r.t. for 1-2 h. After completion of the reaction, the mixture was quenched with H2O and extracted with CH2Cl2 three times. The combined extracts were washed with brine and dried over MgSO4. The solvent was removed under reduced pressure and the crude products were purified by thin-layer chromatography.
