COMMUNICATIONS
Ming-Chang P. Yeh et al.
tracted with diethyl ether (10ꢀ3 mL), and the combined ex-
tracts were washed with brine, dried (MgSO4), and concen-
trated under reduced pressure to give a crude oil. The re-
sulting crude mixture was purified by flash column chroma-
tography over silica gel (hexanes) to afford 2a as a pale
yellow oil; yield: 60 mg (0.26 mmol, 86%).
Supporting Information
Spectroscopic characterization and copies of 1H/13C NMR
spectra of compounds 2a–w, 3, 4a–e, 5a–e, and 7a–d and X-
ray crystallographic information files for compounds 2d, 2f,
2j, and 2p are available in the Supporting Information.
Scheme 3. Synthesis of (E)-5-[(aryl)halomethylene]bicy-
clo[2.2.1]hept-2-enes 7.
Acknowledgements
This work was supported by grants from the Ministry of Sci-
ence and Technology (NSC 101-2113M-003-002-MY3) and
National Taiwan Normal University.
Scheme 4. Plausible reaction path for the FeCl3-promoted
carbochlorination of 1 to 2.
References
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products in 72–85% yield (Scheme 3). In each case,
only a small amount of the (Z)-isomer was isolated
(E/Z> 13:1).
A reaction pathway for the proposed carbochlori-
nation of the six-membered ring 2,6-enynols is sug-
gested in Scheme 4. Detachment of the hydroxy
moiety of 1 by FeCl3 would transiently form the allyl-
ic carbonium 8. Then, anti-addition of a chloride and
the allylic carbonium across the acetylene furnished
the exo-methylene-bridged bicycle 2 with the E-con-
figuration as the major product.
In summary, an efficient and practical method for
the construction of exo-methylene-bridged bicycles
from cyclic 2,6-enynols and a Lewis acid has been de-
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moderate to excellent yields and E/Z selectivities.
The advantages of this procedure are its operational
ease and the mild reaction conditions. Further studies
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Experimental Section
Typical Procedure
To a solution of 4-(3-phenylprop-2-yn-1-yl)cyclohex- 2-enol
(1a) (64 mg, 0.30 mmol in 3.0 mL of dichloromethane
(3.0 mL) was added FeCl3 (97 mg, 0.60 mmol) at room tem-
perature under air. The reaction mixture was stirred until no
trace of 1a was detected on TLC (ca. 2 min). The mixture
was added 3.0 mL of water. The resulting mixture was ex-
4
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