Highly regioselective rearrangement of 2-substituted vinylepoxides catalyzed by gallium(III) triflate

Article abstract of DOI:10.1021/jo050810z

Gallium(III) triflate catalyzed the rearrangement of 2-sub-stituted vinylepoxides into β,γ-unsaturated carbonyl compounds with high regio- and chemoselectivity (>97/3) in low catalyst loading (1-5 mol%). The alkyl-substituted trimethylsilylvinyl epoxides

Full text of DOI:10.1021/jo050810z

SCHEME 1
Highly Regioselective Rearrangement of
2-Substituted Vinylepoxides Catalyzed by
Gallium(III) Triflate
Xian-Ming Deng, Xiu-Li Sun, and Yong Tang*
State Key Laboratory of Organometallic Chemistry,
Shanghai Institute of Organic Chemistry, 354 Fenglin Lu,
Shanghai 200032, China
In a previous study on ylide chemistry,10 we developed
a highly efficient ylide epoxidation of aldhydes with
allylic bromide (eq 1),11 providing an easy access to
2-substituted vinylepoxides but as a mixture of cis and
trans isomers. Very recently, we found that these mixed
tangy@mail.sioc.ac.cn
Received April 21, 2005
epoxides could be chemo- and regioselectively trans-
formed into â,γ-unsaturated carbonyl compounds, poten-
tially useful intermediates in organic synthesis. This
Gallium(III) triflate catalyzed the rearrangement of 2-sub-
stituted vinylepoxides into â,γ-unsaturated carbonyl com-
pounds with high regio- and chemoselectivity (>97/3) in low
catalyst loading (1-5 mol %). The alkyl-substituted tri-
methylsilylvinyl epoxides gave â,γ-unsaturated ketone, but
aryl-substituted vinylepoxides gave the aldehydes instead.
(4) See, for example, the following. Organoaluminum reagent: (a)
Maruoka, K.; Ooi, T.; Yamamoto, H. J. Am. Chem. Soc. 1989, 111, 6431.
(b) Maruoka, K.; Ooi, T.; Nagahara, S.; Yamamoto, H. Tetrahedron
1991, 47, 6983. (c) Maruoka, K.; Ooi, T.; Yamamoto, H. Tetrahedron
1992, 48, 3303. (d) Maruoka, K.; Murase, N.; Bureau, R.; Ooi, T.;
Yamamoto, H. Tetrahedron 1994, 50, 3663. (e) B(C6F5)3: Ishihara, K.;
Hanaki, N.; Yamamoto, H. Synlett 1995, 721. (f) Pd(0) catalyst:
Kulasegaram, S.; Kulawiec, R. J. J. Org. Chem. 1994, 59, 7195. (g)
LiClO4: Sudha, R.; Narasimhan, K. M.; Saraswathy, V. G.; Sankarara-
man, S. J. Org. Chem. 1996, 61, 1877. (h) InCl3: Ranu, B. C.; Jana,
U. J. Org. Chem. 1998, 63, 8212. (i) BiOClO4‚xH2O: Anderson, A. M.;
Blazek, J. M.; Garg, P.; Payne, B. J.; Mohan, R. S. Tetrahedron Lett.
2000, 41, 1527. (j) Bi(OTf)3‚xH2O: Bhatia, K. A.; Eash, K. J.; Leonard,
N. M.; Oswald, M. C.; Mohan, R. S. Tetrahedron Lett. 2001, 42, 8129.
(k) VO(OEt)Cl2: Mart´ınez, F.; Campo, C.; Llama, E. F. J. Chem. Soc.,
Perkin Trans. 1 2000, 1749. (l) Er(OTf)3: Procopio, A.; Dalpozzo, R.;
Nino, A. D.; Nardi, M.; Sindona, G.; Tagarelli, A. Synlett 2004, 2633.
(5) For metalloporphyrin-catalyzed rearrangement, see the follow-
ing. (a) Fe(TPP)OTf: Takanami, T.; Hirabe, R.; Ueno, M.; Hino, F.;
Suda, K. Chem. Lett. 1996, 1031. (b) Fe(TPP)ClO4: Suda, K.; Baba,
K.; Nakajima, S.; Takanami, T. Tetrahedron Lett. 1999, 40, 7243. (c)
Suda, K.; Baba, K.; Nakajima, S.; Takanami, T. Chem. Commun. 2002,
2570. (d) Cr(TPP)OTf: Suda, K.; Kikkawa, T.; Nakajima, S.; Takanami,
T. J. Am. Chem. Soc. 2004, 126, 9554.
(6) For recent acid-catalyzed rearrangement of enol ester epoxides,
see: (a) Zhu, Y.; Manske, K. J.; Shi, Y. J. Am. Chem. Soc. 1999, 121,
4080. (b) Feng, X.; Shu, L.; Shi, Y. J. Am. Chem. Soc. 1999, 121, 11002.
(c) Zhu, Y.; Shu, L.; Tu, Y.; Shi, Y. J. Org. Chem. 2001, 66, 1818. (d)
Feng, X.; Shu, L.; Shi, Y. J. Org. Chem. 2002, 67, 2831.
(7) Rosenberger, M.; Jackson, W.; Saucy, G. Helv. Chim. Acta 1980,
63, 175.
(8) Stoichiometric BF3-promoted rearrangements of vinyl epoxides:
(a) Jung, M. E.; D’Amico, D. C. J. Am. Chem. Soc. 1995, 117, 7379. (b)
Jung, M. E.; Anderson, K. L. Tetrahedron Lett. 1997, 38, 2605. (c) Jung,
M. E.; Marquez R. Tetrahedron Lett. 1999, 40, 3129.
(9) For rearrangement catalyzed by Pd(0), see: (a) Gilloir, F.;
Malacria, M. Tetrahedron Lett. 1992, 33, 3859. (b) Bideau, F. L.;
Aubert, C.; Malacria, M. Tetrahedron: Asymmetry 1995, 6, 697. (c)
Bideau, F. L.; Gilloir, F.; Nilson, Y.; Aubert, C.; Malacria, M. Tetra-
hedron 1996, 52, 7487. (d) Courillon, C.; Fol, R. L.; Vandendris, E.;
Malacria, M. Tetrahedron Lett. 1997, 38, 5493.
Lewis acid promoted rearrangement of epoxides into
carbonyl compounds is one of the most useful tools in
organic synthesis1 and has been widely applied to the
preparation of various biologically active natural and
non-natural products.2 As involved in chemoselectivity
and regioselectivity, the product distribution of the
rearrangement of epoxides depends on promoter/catalyst
and substrates as well as reaction conditions.1,3 Of the
substrates investigated, aryl-, alkyl-, and acyloxy-sub-
stituted epoxides are well-studied.4-6 However, few re-
ports7 on the Lewis acid catalyzed rearrangement of
vinylepoxides appeared in the literature except for a few
examples of those related to trisubstituted ones8 pro-
moted by stoichiometric Lewis acids.9 In this paper, we
wish to report a highly chemoselective and regioselective
rearrangement of 2-substituted vinylepoxides into â,γ-
unsaturated carbonyl compounds catalyzed by Ga(OTf)3
(Scheme 1).
(1) For reviews, see: (a) Parker, R. E.; Issacs, N. S. Chem. Rev. 1959,
59, 737. (b) Rao, A. S.; Paknikar, S. K.; Kirtane, J. G. Tetrahedron
1983, 39, 2323. (c) Smith, J. G. Synthesis 1984, 629.
(2) For a review, see: Silva, L. F., Jr. Tetrahedron 2002, 58, 9137.
Selected references: (a) Kita, Y.; Higuchi, K.; Yoshida, Y.; Iio, K.;
Kitagaki, S.; Uede, K.; Akai, S.; Fujioka, H. J. Am. Chem. Soc. 2001,
123, 3214. (b) Grellepois, F.; Chorki, F.; Crousse, B.; Oure´vitch, M.;
Bonnet-Delpon, D.; Be´gue´, J. P. J. Org. Chem. 2002, 67, 1253. (c)
Kimura, T.; Yamamoto, N.; Suzuki, Y.; Kawano, K.; Norimine, Y.; Ito,
K.; Nagato, S.; Iimura, Y.; Yonaga, M. J. Org. Chem. 2002, 67, 6228.
(d) T¢nder, J. E.; Tanner, D. Tetrahedron 2003, 59, 6937.
(10) (a) Huang, Z.-Z.; Ye, S.; Xia, W.; Tang, Y. Chem. Commun. 2001,
1384. (b) Ye, S.; Huang, Z.-Z.; Xia, C.-A.; Tang, Y.; Dai, L.-X. J. Am.
Chem. Soc. 2002, 124, 2432. (c) Liao, W.-W.; Li, K.; Tang, Y. J. Am.
Chem. Soc. 2003, 125, 13030. (d) Huang, Z.-Z.; Ye, S.; Xia, W.; Yu,
Y.-H.; Tang, Y. J. Org. Chem. 2002, 67, 3096. (e) Huang, Z.-Z.; Tang,
Y. J. Org. Chem. 2002, 67, 5320.
(3) For a review, see: Rickborn, B. Acid-catalyzed Rearrangements
of Epoxides in Comprehensive Organic Synthesis; Trost, B. M., Fleming,
I., Eds.; Pergamon Press: Oxford, U.K., 1991; Vol. 3.3, pp 733-775.
(11) (a) Li, K.; Huang, Z.-Z.; Tang, Y. Tetrahedron Lett. 2003, 44,
2605. (b) Li, K.; Deng, X.-M.; Tang, Y. Chem. Commun. 2003, 2074.
10.1021/jo050810z CCC: $30.25 © 2005 American Chemical Society
Published on Web 06/30/2005
J. Org. Chem. 2005, 70, 6537-6540
6537

TABLE 1. Effects of Reaction Conditions on the
Rearrangement of Epoxide 1a
TABLE 2. Ga(OTf)3-Catalyzed Rearrangement of Vinyl
Epoxides
Lewis acid
(mol %)
yieldb
entry
reaction conditions
2a/3aa (%)
1
2
3
4
5
6
7
8
9
SnCl4 (100)
CH2Cl2/45 min/-78 °C
c
0
0
0
48
68
80
78
92
87
Ti(OPri)4 (10) CH2Cl2/24 h/-78 °C f reflux
LiOTf (10)
CH2Cl2/18 h/25 °C f reflux
Mg(OTf)2 (10) CH2Cl2/18 h/25 °C f reflux
Y(OTf)3 (10) CH2Cl2/18 h/25 °C f reflux
Ga(OTf)3 (10) CH2Cl2/30 min/25 °C
Ga(OTf)3 (5) CH2Cl2/1.5 h/0 °C
13/87
33/67
8/92
9/91
6/94
3/97
Ga(OTf)3 (5) ClCH2CH2Cl/1.5 h/0 °C
Ga(OTf)3 (5) toluene/1.5 h/0 °C
10 Ga(OTf)3 (5) toluene/2 h/-10 °C
a Determined by 1H NMR. b Isolated yield. c Complicated.
transformation proved Lewis acid and solvent dependent.
As shown in Table 1, the rearrangement of 2-cyclohexyl-
silylvinylepoxide 1a in the presence of stoichiometric
SnCl4 gave disordered products in dichloromethane (en-
try 1, Table 1). Attempts using a catalytic amount (10
mol %) of commonly used Lewis acids such as Ti(OPri)4,
LiOTf, and Mg(OTf)2 failed in dichloromethane, and no
desired products were obtained (entries 2-4, Table 1).
Y(OTf)3 (10 mol %)could promote the reaction under
reflux in CH2Cl2 to afford a mixture of aldehyde 2a and
ketone 3a with a ratio of 13:87 (entry 5) in 48% yield.
Fortunately, 10 mol % of Ga(OTf)3 catalyzed the rear-
rangement well to give the desired products in reasonable
yields at room temperature, although the regioselectivity
was not good. Further studies showed that the ratio of
3a and 2a could be improved from 33/67 to 8/92 by
lowering the reaction temperature from 25 to 0 °C and
even the catalyst loading was reduced to 5 mol % (entries
6 and 7). Replacement of the solvent with toluene gave
better results (entries 9 and 10) compared with those in
CH2Cl2. In our screened conditions, the best result was
achieved using gallium(III) triflate as the catalyst and
toluene as the solvent at -10 °C. In this case, the
rearrangement gave the aldehyde in 87% yield with
excellent chemo- and regioselectivity (2a/3a, 3/97, entry
10).
To study the generality of the rearrangement, a variety
of 1,2-disubstitued trimethylsilylvinyl epoxides and trisub-
stituted trimethylsilylvinyl epoxide were examined under
the optimal conditions. As summarized in Table 2, the
regioselectivity was substrate dependent. 2-Alkyl-sub-
stituted trimethylsilylvinyl epoxides regioselectively gave
â,γ-unsaturated ketone 3, via a hydrogen migration, as
major products in high yields (entries 1 and 2, Table 2)
while aryl-substituted vinylepoxides gave the aldehydes
2 in lieu of ketones as single products in high yields
(entries 3-8, Table 2). In addition, aryl-substituted vinyl
epoxides proved more active than alkyl-substituted ones,
and the loading of Ga(OTf)3 could be reduced to 1 mol %.
In the case of aryl-substituted vinylepoxides used, the
reactions were very clean and the purification procedure
a Determined by 1H NMR. b Isolated yields. c The ratio for trans
and cis isomers. d 5 mol % of Ga(OTf)3 in toluene at -10 °C. e 1
mol % of Ga(OTf)3 in CH2Cl2 at 0 °C. f Ratio for E and Z isomers.
g Isolated total yield of Z and E isomers.
was very simple (entries 3-8, Table 2). The pure product
could be obtained just by filtering the catalyst off by a
short silica gel column followed by concentration. The
substitution on the aryl ring has almost no effects on both
yields and selectivity. Trisubstituted oxirane 1h also
worked well and afforded quaternary aldehyde (entry 8,
Table 2). Noticeably, the stereochemistry of the product
is substrate independent. In all cases investigated (entries
1-8, Table 2), a mixture of cis and trans isomers of
epoxides gave â,γ-unsaturated carbonyl compounds with
high E stereoselectivity. Unlike that the silylvinyl-
substituted epoxides were transformed into â,γ-unsatur-
ated aldehydes, simple vinyl-substituted epoxides gave
a mixture of E- and Z-R,â-unsaturated aldehydes 4i and
4j (entries 9 and 10, Table 2) as the final products under
the same reaction conditions, demonstrating trimethyl-
silyl in the vinyl group inhibited the isomerization of â,γ-
unsaturated aldehydes into R,â-unsaturated aldehydes
and was important to control the stereoselectivity of the
products.
The â,γ-unsaturated aldehydes with a vinlysilane
group12 prepared by the current method should be
synthetically useful. For example, aldehyde 2c could be
readily transformed into trisubtituted olefin 4i-E in the
(12) For reviews on transformation of vinylsilane, see: (a) Fleming,
I.; Dunogues, J.; Smithers, R. Org. React. 1989, 37, 57. (b) Weber, W.
P. Silicon Reagents for Organic Synthesis; Springer-Verlage: Berlin,
1983. (c) Colvin, E. W. Silicon in Organic Synthesis; Butterworths:
London, 1983.
6538 J. Org. Chem., Vol. 70, No. 16, 2005

(3) (E)-2-(4-Chlorophenyl)-4-(trimethylsilyl)but-3-enal
(2c). Yield: 98%. IR (film) ν/cm-1: 2956 (m), 1726 (s), 1607 (w),
1492 (m), 1249 (m), 867 (m), 840 (m). 1H NMR (300 MHz, CDCl3/
TMS) δ: 9.66 (d, J ) 2.4 Hz, 1H), 7.38-7.34 (m, 2H), 7.16-7.13
(m, 2H), 6.23 (dd, J ) 6.0, 18.6 Hz, 1H), 5.85 (dd, J ) 1.5, 18.9
Hz, 1H), 4.28 (dt, J ) 1.8, 6.6 Hz, 1H), 0.09 (s, 9H). 13C NMR
(75 MHz, CDCl3): 198.0, 139.3, 136.8, 133.8, 133.5, 130.2, 129.1,
64.2, -1.5. MS (EI, m/z, rel intensity): 252 (M+, 19.92), 237
(11.65), 223 (14.03), 115 (24.14), 75 (14.69), 73 (100), 45 (13.48).
HRMS: calcd for C13H17ClOSi 252.0737, found 253.0810 (M +
H+).
SCHEME 2
(4) (E)-2-Phenyl-4-(trimethylsilyl)but-3-enal (2d). Yield:
95%. IR (film) ν/cm-1: 2955 (m), 1726 (s), 1600 (m), 1493 (w),
1453 (w), 1248 (m), 868 (m), 839 (m), 755 (w), 699 (m). 1H NMR
(300 MHz, CDCl3/TMS) δ: 9.68 (d, J ) 2.4 Hz, 1H), 7.44-7.31
(m, 3H), 7.25-7.22 (m, 2H), 6.30 (dd, J ) 6.0, 18.9 Hz, 1H), 5.87
(dd, J ) 1.5, 18.9 Hz, 1H), 4.30 (dt, J ) 1.8, 4.2 Hz, 1H), 0.10 (s,
9H). 13C NMR (75 MHz, CDCl3): 198.5, 139.9, 136.2, 135.4,
129.0, 128.9, 127.6, 65.0, -1.4. MS (EI, m/z, rel intensity): 218
(M+, 2.58), 189 (13.36), 129 (8.01), 105 (10.10), 75 (13.46), 74
(9.79), 73 (100.0), 45 (8.41). HRMS: calcd for C13H18OSi 218.1127,
found 219.1200 (M + H+).
(5) (E)-2-(4-Bromophenyl)-4-(trimethylsilyl)but-3-enal
(2e). Yield: 95%. IR (film) ν/cm-1: 2955 (m), 1725 (s), 1683 (m),
1488 (s), 1248 (s), 866 (s), 840 (s). 1H NMR (300 MHz, CDCl3/
TMS) δ: 9.66 (d, J ) 2.4 Hz, 1H), 7.54-7.50 (m, 2H), 7.11-7.07
(m, 2H), 6.22 (dd, J ) 6.6, 18.9 Hz, 1H), 5.85 (dd, J ) 1.5, 18.9
Hz, 1H), 4.26 (dt, J ) 1.8, 6.3 Hz, 1H), 0.09 (s, 9H). 13C NMR
(75 MHz, CDCl3): 197.9, 139.2, 136.9, 134.3, 132.1, 130.6, 121.7,
64.2, -1.4. MS (EI, m/z, rel intensity): 292 (M+, 2.20), 131
(100.0), 115 (25.07), 103 (53.39), 102 (52.54), 84 (26.98), 75
(40.64), 73 (85.61). HRMS: calcd for C13H17BrOSi 296.0232,
found 297.0305 (M + H+).
(6) (E)-2-(4-Methoxyphenyl)-4-(trimethylsilyl)but-3-enal
(2f). Yield: 93%. IR (film) ν/cm-1: 2955 (s), 1724 (s), 1611 (m),
1512 (s), 1250 (m), 867 (m), 839 (m). 1H NMR (300 MHz, CDCl3/
TMS) δ: 9.63 (d, J ) 2.1 Hz, 1H), 7.12 (dd, J ) 2.1, 6.0 Hz, 2H),
6.92 (dd, J ) 2.1, 6.6 Hz, 2H), 6.25 (dd, J ) 6.0, 18.9 Hz, 1H),
5.81 (dd, J ) 1.5, 18.6 Hz, 1H), 4.22 (dt, J ) 2.1, 6.3 Hz, 1H),
3.79 (s, 3H), 0.07 (s, 9H). 13C NMR (75 MHz, CDCl3): 198.8,
159.0, 140.2, 135.8, 129.9, 127.2, 114.4, 64.0, 55.2, -1.4. MS (EI,
m/z, rel intensity): 248 (M+, 29.98), 162 (29.31), 161 (26.77),
147 (20.54), 131 (26.60), 121 (26.63), 73 (95.14). HRMS: calcd
for C14H20O2Si 248.1233, found 249.1305 (M + H+).
(7) (E)-2-(Naphthalen-1-yl)-4-(trimethylsilyl)but-3-enal
(2g). Yield: 98%. IR (film) ν/cm-1: 3049 (w), 2955 (m), 1724 (s),
1248 (m), 867 (m), 840 (m). 1H NMR (300 MHz, CDCl3/TMS) δ:
9.78 (d, J ) 1.8 Hz, 1H), 7.97-7.86 (m, 3H), 7.56-7.51 (m, 3H),
7.43 (dd, J ) 1.2, 6.9 Hz, 1H), 6.54 (dd, J ) 5.4, 18.6 Hz, 1H),
5.88 (dd, J ) 1.5, 18.6 Hz, 1H), 5.00 (dt, J ) 1.5, 5.4 Hz, 1H),
0.13 (s, 9H). 13C NMR (75 MHz, CDCl3): 199.0, 140.0, 135.9,
134.1, 131.7, 128.9, 128.5, 127.2, 126.5, 125.9, 125.5, 123.5,61.1,
-1.4. MS (EI, m/z, rel intensity): 268 (M+, 4.79), 181 (66.00),
165 (43.02), 153 (91.03), 152 (100), 151 (35.0), 147 (33.26), 75
(25.65), 73 (66.66). HRMS: calcd for C17H20OSi 268.1283, found
291.1176 (M + Na+).
presence of silica gel (Scheme 2), providing an easy access
to E-trisubstitued R,â-unsaturated aldehydes with high
stereoselectivity (E/Z > 50/1). The aldehyde 2c could also
be converted to homoallylic alcohol 5c by reduction with
NaBH4.
In summary, we developed an efficient gallium triflate
catalyzed rearrangement of 2-substituted vinyl epoxides
into â,γ-unsaturated carbonyl compounds with high
regio- and chemoselectivity (>97/3). The low catalyst
loading (1-5 mol %), the mild conditions, the multifunc-
tionalized products, and in particular, the use of readily
available cis/trans-vinyl epoxides as materials make the
current method useful for practical use in organic syn-
thesis.
Experimental Section
General Procedure for Rearrangement of Alkylvinyl
Epoxides. To a solution of the epoxide (0.45 mmol) in toluene
(3 mL) was added Ga(OTf)3 (11.6 mg, 5 mol %). The resulting
mixture was stirred at -10 °C under N2 atmosphere. After the
reaction was complete (monitored by TLC), it was washed with
water followed by sodium bicarbonate aqueous solution and
saturated brine solution. The organic layer was collected and
dried by anhydrous Na2SO4 and then concentrated under
reduced pressure. The residue was purified by flash chroma-
tography to give the pure product.
(1) (E)-1-Cyclohexyl-4-(trimethylsilyl)but-3-en-1-one (3a).
Yield: 87%. IR (film) ν/cm-1: 2931 (s), 2854 (s), 1710 (s), 1615
(w), 1450 (m), 1247 (m), 863 (s), 838 (s). 1H NMR (300 MHz,
CDCl3/TMS) δ: 6.10 (dt, J ) 6.6, 12.3 Hz, 1H), 5.74 (dt, J ) 1.5,
17.4 Hz, 1H), 3.25 (dd, J ) 1.2, 6.9 Hz, 2H), 2.40-2.32 (m, 1H),
1.85-1.62 (m, 5H), 1.34-1.16 (m, 5H), 0.06 (s, 9H). 13C NMR
(75 MHz, CDCl3): 211.8, 138.3, 134.9, 50.5, 48.6, 28.3, 25.8, 25.6,
-1.4. MS (EI, m/z, rel intensity): 223 (M+, 1.96), 209 (18.23),
208 (77.02), 134 (49.27), 111 (19.76), 83 (25.47), 75 (15.09), 73
(100.00). HRMS: calcd for C13H24OSi 224.1596, found 225.1669
(M + H+).
(2) (E)-1-(Trimethylsilyl)tridec-1-en-4-one (3b). Yield:
93%, IR (film) ν/cm-1: 2955 (s), 2926 (s), 2855 (s), 1718 (s), 1248
(s), 863 (s), 839 (s). 1H NMR (300 MHz, CDCl3/TMS) δ: 6.06
(dt, J ) 6.6, 12.6 Hz, 1H), 5.76 (dt, J ) 1.5, 17.4 Hz, 1H), 3.21
(dd, J ) 1.5, 6.6 Hz, 2H), 2.41 (t, J ) 6.6 Hz, 2H), 1.60-1.50 (m,
2H), 1.35-1.18 (m, 12H), 0.86 (t, J ) 6.6 Hz, 3H), 0.06 (s, 9H).
13C NMR (75 MHz, CDCl3): 209.1, 138.0, 135.2, 50.8, 42.4, 31.8,
29.40, 29.39, 29.24, 29.16, 23.7, 22.6, 14.1, -1.4.. MS (EI, m/z,
rel intensity): 269 (M+, 12.12), 169 (42.88), 156 (33.80), 155
(100.00), 85 (43.98), 73 (45.05), 71 (61.00), 43 (72.67). HRMS:
calcd for C16H32OSi 268.2222, found 269.2295 (M + H+).
General Procedure for Rearrangement of Arylvinyl
Epoxides. To a solution of the epoxide (0.5 mmol) in CH2Cl2
(2.5 mL) was added Ga(OTf)3 (2.6 mg, 1 mol %). The resulting
mixture was stirred at 0 °C under N2 atmosphere. After the
reaction was completed (monitored by TLC), the mixture was
diluted with CH2Cl2 and rapidly filtered through a glass funnel
with a thin layer of silica gel (eluted with CH2Cl2). The filtrate
was collected and concentrated under reduced pressure to give
the pure product.
(8) (E)-2-(4-Fluorophenyl)-2-methyl-4-(trimethylsilyl)-
but-3-enal (2h). Yield: 76%. IR (film) ν/cm-1: 2956 (s), 1729
1
(s), 1604 (m), 1509 (s), 1249 (s), 866 (s), 839 (s). H NMR (300
MHz, CDCl3/TMS) δ: 9.55 (s, 1H), 7.21-7.04 (m, 4H), 6.29 (d, J
) 19.2 Hz, 1H), 5.87 (d, J ) 19.2 Hz, 1H), 1.49 (s, 3H), 0.12 (s,
9H). 13C NMR (75 MHz, CDCl3). 199.2, 162.0 (d, JC-F ) 245.6
Hz), 144.7, 136.1 (d, JC-F ) 2.8 Hz), 134.0, 129.2 (d, JC-F ) 8.2
Hz), 115.8 (d, JC-F ) 21.2 Hz), 58.9, 20.6, -1.3. MS (EI, m/z,
rel intensity): 250 (M+, 5.41), 221 (18.84), 139 (15.48), 129
(28.24), 127 (16.39), 75 (16.76), 73 (100), 43 (13.65). Anal. Calcd
for C14H19FOSi: C, 67.16; H, 7.65. Found: C, 66.78; H, 7.86.
(9) (E)-2-(4-Chlorophenyl)but-2-enal (4i-E).13 The total
1
yield of E and Z isomers (E/Z ) 77/23) was 61%. H NMR (300
(13) Dana, G.; Thuan, S. L. T.; Gharbi-Benarous, J. Bull. Soc. Chim.
Fr. 1974, 2089.
J. Org. Chem, Vol. 70, No. 16, 2005 6539

MHz, CDCl3/TMS) for E-isomer δ: 9.59 (s, 1H), 7.41-7.36 (m,
2H), 7.13-7.10 (m, 2H), 6.87 (q, J ) 7.2 Hz, 1H), 2.01 (d, J )
6.9 Hz, 3H).
centrated under reduced pressure. The residue was purified by
flash chromatography to give 5c as white solid. Yield: 86%. Mp:
75-77 °C. IR (KBr) ν/cm-1: 3268 (w, br), 2953 (m), 1608 (w),
1
(10) (E)-2-(4-Methoxyphenyl)but-2-enal (4j-E). The total
yield of E and Z isomers (E/Z ) 91/9) was 65%. IR (film) ν/cm-1
for E-isomer: 2956 (w), 2837 (w), 1688 (s), 1607 (m), 1514 (s),
1463 (w), 1249 (s), 842 (m), 805 (m). 1H NMR (300 MHz, CDCl3/
TMS) δ: 9.56 (s, 1H), 7.11-7.08 (m, 2H), 6.94-6.90 (m, 2H),
6.77 (q, J ) 7.2 Hz, 1H), 3.79 (s, 3H), 1.99 (d, J ) 7.2 Hz, 3H).
13C NMR (75 MHz, CDCl3): 193.8, 159.1, 151.0, 144.3, 130.6,
124.2, 113.6, 55.1, 15.9. MS (EI, m/z, rel intensity) 176 (M+,
100), 147 (61.78), 135 (32.07), 132 (21.39), 117 (20.60), 115
(31.33), 91 (37.19), 77 (23.23). HRMS: calcd for C11H12O2
176.0837, found 199.0730 (M + Na+).
1491 (m), 1246 (s), 866 (s), 836 (s). H NMR (300 MHz, CDCl3/
TMS): δ 7.34-7.29 (m, 2H), 7.18-7.15 (m, 2H), 6.11 (dd, J )
6.9, 18.6 Hz, 1H), 5.81 (dd, J ) 1.2, 18.6 Hz, 1H), 3.85-3.75 (m,
2H), 3.55 (dd, J ) 6.3, 13.8 Hz, 1H), 1.52 (s, br, 1H), 0.06 (s,
9H). 13C NMR (75 MHz, CDCl3): 144.9, 139.2, 133.3, 132.5,
129.4, 128.7, 65.7, 54.1, -1.3. MS (EI, m/z, rel intensity): 254
(M+, 1.02), 225 (10.39), 224 (16.17), 223 (22.31), 129 (12.39), 115
(18.79), 75 (27.44), 73 (100.00). Anal. Calcd for C13H19ClOSi: C,
61.27; H, 7.52. Found: C, 61.37; H, 7.55.
Acknowledgment. We are grateful for financial
support from the Natural Sciences Foundation of China
and The Science and Technology Commission of Shang-
hai Municipality.
(11) Synthesis of (E)-2-(4-chlorophenyl)but-2-enal13 (4i-
E). Aldehyde 2c was chromatographed on silica gel to give pure
product. Total yield of E and Z isomers (E/Z > 50/1) was 88%.
(12) Synthesis of (E)-2-(4-Chlorophenyl)-4-(trimethyl-
silyl)but-3-en-1-ol (5c). To a solution of aldehyde 2c (126.4 mg,
0.5 mmol) in MeOH (10 mL) at 0 °C was added NaBH4 (20 mg).
After 15 min, the reaction mixture was acidified slowly by
addition of hydrogen chloride solution (2 N) to PH ) 4. To the
resulting mixture was added 10 mL of water, and the mixture
was extracted with dichloromethane (3 × 15 mL). The combined
organic extracts were dried over anhydrous Na2SO4 and con-
Supporting Information Available: NMR spectra of new
compounds and experimental details for the preparation of
vinyloxiranes 2g and 2h. This material is available free of
charge via the Internet at http://pubs.acs.org.
JO050810Z
6540 J. Org. Chem., Vol. 70, No. 16, 2005