References and Notes
Pioneering works of cyclization triggered by alkyne activation using Au catalyst:
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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 .
<A NAME="RU30105ST-10">10 </A>
Cationic platinum, which was prepared from PtCl2 (1 mol%) and AgOTf (2.5 mol%), did not work as a catalyst even in refluxed CH2 Cl2 .
<A NAME="RU30105ST-11">11 </A>
Typical Experimental Procedure (Table 2).
AuCl(PPh3 ) (1.2 mg, 0.0024 mmol) was placed in a flask and a CH2 Cl2 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 H2 O and extracted with CH2 Cl2 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.
<A NAME="RU30105ST-12">12 </A>
(1-Methylnaphthalen-3-yl)methanol (2f ): yellow oil. IR (neat): 3350, 872, 773, 748 cm-1 . 1 H 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). 13 C 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 C12 H12 O [M+ ]: 172.0888; found: 172.0891.
<A NAME="RU30105ST-13">13 </A>
The stereochemistry of alkene moiety was determined by NOE observation (Figure
[1 ]
).
Figure 1
<A NAME="RU30105ST-14">14 </A>
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).
<A NAME="RU30105ST-15">15 </A> (1E )-1-(Iodomethylene)-3-methyl-1H -indene (3m ): yellow oil. IR (neat): 1110, 1079, 1019 cm-1 . 1 H 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). 13 C 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 C11 H9 I [M+ ]: 267.9749; found: 267.9747
<A NAME="RU30105ST-16">16 </A>
During the purification of the products, some vinyl iodide (E )-3m was isomerized to (Z )-3m .