M. Kodomari et al. / Tetrahedron Letters 42 (2001) 3105–3107
3107
Br
6a Ar = C6H5 99%
KOH
MeOH
reflux / 1 h
Ph
Ph
Ar
Ar
6b Ar = p-Cl-C6H4 97%
H
6
5
Scheme 3.
Scheme 4.
O
X
-CH3COOH
Ar
O
X
O
R
O
X
CH3
R
R
+
H3C
Ar
Ar
H
(Scheme 2). Ethyl phenyl ketone afforded the corre-
sponding chlorostyrene in 91% yield, whereas acetophe-
none did not react with acetyl chloride and unchanged
acetophenone was recovered. Naphtyl ketones and
acylthiophenes also react with acetyl halides to give the
corresponding halo olefins in high yields. For example,
reaction of 2-methyl-4-butyrylthiophene with acetyl
chloride in the presence of ZnCl2/SiO2 was carried out
in 1,2-dichloroethane at 30°C for 0.5 h to afford the
corresponding vinyl chloride in 91% yield (entry 18).
The bromostilbene products were easily transformed
into the corresponding alkynes through elimination
reaction with potassium hydroxide/methanol (Scheme
3).
conditions; (c) high yield; (d) stereoselectivity; and (e)
no phosphorous-containing reagents are used. We
believe this will provide a better and more practical
alternative to the existing methodologies for the synthe-
sis of aryl-substituted halo olefins.
References
1. Boutagy, J.; Thomas, R. Chem. Rev. 1974, 74, 87.
2. Kumaraswamy, S.; Kumara Swamy, K. C. Tetrahedron
Lett. 1997, 38, 2183.
3. Petrova, J.; Coutrot, P.; Dreux, M.; Savignac, P. Synthe-
sis 1975, 658.
4. Huang, Z. Z.; Lan, G. C.; Haung, X. Synth. Commun.
1998, 28, 633.
This route to aryl-substituted halo olefins from ketones
and acetyl halide is different from the mechanism pro-
posed by Bastock et al.7 for the formation of
chlorostyrene products in the reaction of anisole with
acyl chloride. Either acetyl chloride or phenylacetyl
chloride in the reaction with a ketone afforded the same
chlorostyrene product. From these results, the forma-
tion of halo olefins in the reaction of ketones with
acetyl halides probably proceeds through addition of
acetyl halides to the carbonyl, resulting in an a-haloac-
etate, followed by elimination of acetic acid.5
5. Moughamir, K.; Mezgueldi, B.; Atmani, A.; Mestdagh,
H.; Rolando, C. Tetrahedron Lett. 1999, 40, 59.
6. Kodomari, M.; Taguchi, S. J. Chem. Res. (S) 1996, 240.
7. Bastock, T. W.; Clark, J. H.; Landon, P.; Martin, K. J.
Chem. Res. (S) 1994, 104.
8. Silica gel-supported zinc chloride was prepared as fol-
lows. Silica gel (Wakogel C-200, 40 g) was added to a
solution of zinc chloride (10 g) in water (100 ml) and the
mixture was stirred at room temperature for 0.5 h. The
water was removed by rotary evaporation and the result-
ing reagent was then dried in vacuo (15 mmHg) at 150°C
for 12 h.
Acetyl halides add to the carbonyl of aldehydes to give
a-haloacetate in the presence of zinc chloride12 (Scheme
9. Cristol, S. J.; Whittemore, C. A. J. Org. Chem. 1969, 34,
705.
4).
10. Fahey, R. F.; Schubert, C. J. Am. Chem. Soc. 1965, 87,
5172.
11. Yamaguchi, A.; Okazaki, M. Nippon Kagaku Kaishi 1972,
2103.
12. Bigler, P.; Muhler, H.; Neuenschwander, M. Synthesis
1978, 593.
In conclusion, the present procedure using silica gel-
supported ZnCl2 provides an efficient synthesis of aryl-
substituted halo olefins from readily available aromatic
ketones and acetyl halides. The notable advantages of
this procedure are: (a) operational simplicity; (b) mild
.
.