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DOI: 10.1055/s-2006-926261
Cationic Au(I)-Catalyzed Cycloisomerization of Aromatic Enynes for the Synthesis of Substituted Naphthalenes
Publication History
Publication Date:
06 February 2006 (online)
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Abstract
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.
Key words
cycloisomerization - catalysis - enynes - gold - indenes - naphthalenes
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1a
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Fürstner A.Mamane V. Chem. Commun. 2003, 2112 - 15 (1E)-1-(Iodomethylene)-3-methyl-1H-indene (3m): yellow oil. IR (neat): 1110, 1079, 1019 cm-1. 1H NMR (400 MHz, CDCl3): δ = 2.16 (s, 3 H), 6.35 (s, 1 H), 7.14-7.29 (m, 4 H), 7.39 (d, 1 H, J = 7.2 Hz). 13C NMR (100 MHz, CDCl3): δ = 13.5, 79.1, 119.1, 125.1, 125.7, 126.5, 127.8, 135.6, 144.3, 145.9, 150.0. HRMS (FAB): m/z calcd for C11H9I [M+]: 267.9749; found: 267.9747
References and Notes
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.
10Cationic platinum, which was prepared from PtCl2 (1 mol%) and AgOTf (2.5 mol%), did not work as a catalyst even in refluxed CH2Cl2.
11
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.
(1-Methylnaphthalen-3-yl)methanol (2f): yellow oil. IR (neat): 3350, 872, 773, 748 cm-1. 1H NMR (600 MHz, CDCl3): δ = 1.92 (br s, 1 H), 2.68 (s, 3 H), 4.79 (s, 2 H), 7.31 (s, 1 H), 7.47-7.52 (m, 2 H), 7.64 (s, 1 H), 7.81-7.82 (m, 1 H), 7.96-7.97 (m, 1 H). 13C NMR (100 MHz, CDCl3): δ = 19.4, 65.4, 123.7, 123.9, 125.6, 125.7, 125.8, 128.4, 132.0, 133.4, 134.7, 137.8. HRMS (FAB): m/z calcd for C12H12O [M+]: 172.0888; found: 172.0891.
13The stereochemistry of alkene moiety was determined by NOE observation (Figure [1] ).
Figure 1
In the presence of AuCl3 (5 mol%) as a catalyst, almost no cycloisomerization of 1j proceeded even at 80 °C in toluene (see ref. 5).
16During the purification of the products, some vinyl iodide (E)-3m was isomerized to (Z)-3m.