M. Tokunaga et al. / Journal of Organometallic Chemistry 690 (2005) 5378–5382
5381
In conclusion, we have performed copper-catalyzed
oxidative C@C bond cleavage of aromatic enol ethers.
The reaction employs rather mild condition compared
with known methods in other alkenes using molecular
oxygen ([3b] and references sited therein). Further inves-
tigation on the mechanism and synthetic applications
are now in progress.
1-Methoxy-2-(p-chlorophenyl)propene (1d) (E/Z =
1:1.1). 1H NMR (CDCl3, 400 MHz): (E)-isomer;
d 1.95 (3H, d, J = 1.4 Hz), 3.71 (3H, s), 6.39 (1H, d,
J = 1.4 Hz), 7.19–7.28 (4H, m), (Z)-isomer; d 1.88 (3H,
d, J = 1.4 Hz), 3.67 (3H, s), 6.12 (1H, d, J = 1.4 Hz),
7.19–7.28 (2H, m), 7.51–7.56 (2H, m). 13C NMR
(C6D6, 100 MHz): (E)-isomer; d 12.5, 60.1, 113.5,
126.2 (2C), 128.5 (2C), 131.5, 139.2, 145.5, (Z)-isomer;
d 18.2, 60.3, 109.7, 128.0 (2C), 128.8 (2C), 131.5,
136.8, 145.2; EI-MS: C10H11ClO+ requires m/z =
182.0498, found: 182.0487.
2. Experimental
1-Methoxy-2-(p-fluorophenyl)propene (1e) (E/Z =
1
1:1.1). H NMR (C6D6, 400 MHz): (E)-isomer; d 1.94
2.1. Preparation and characterization of the substrates
(3H, d, J = 1.4 Hz), 3.11 (3H, s), 6.00 (1H, d, J = 1.4
Hz), 6.75–6.94 (4H, m), (Z)-isomer; d 1.65 (3H, d,
J = 1.4 Hz), 3.00 (3H, s), 5.66 (1H, d, J = 1.4 Hz),
6.85–6.90 (2H, m), 7.52–7.56 (2H, m). 13C NMR
(C6D6, 100 MHz): (E)-isomer; d 12.6, 59.0, 113.2,
115.0 (2C, d, J = 21 Hz) 126.5 (2C, d, J = 7.7 Hz),
134.6 (d, J = 2.9 Hz), 145.1, 161.6 (d, J = 244 Hz), (Z)-
isomer; d 18.0, 59.3, 109.4, 114.5 (2C, d, J = 21 Hz)
129.3 (2C, d, J = 7.7 Hz), 134.6 (d, J = 2.9 Hz), 144.5,
161.2 (d, J = 246 Hz); Anal. Calc. for C10H11FO: C,
72.27; H, 6.67. Found: C, 72.78; H, 6.80.
Enol ethers 1 were synthesized by the procedures as
described below and determination of E/Z stereochemis-
try were carried out by 1H NMR, DPFGSE-NOE meth-
od [8] (double pulse field gradient spin echo), which
gives nearly identical results to a conventional NOE dif-
ference experiment with better S/N ratio. Assignment of
1H and 13C chemical shifts was based on HMQC and
HMBC experiments.
1-Methoxy-2-phenylpropene (1a) was synthesized
from 2-phenylpropionaldehyde by a literature method
[9a]. A mixture of 2-phenylpropionaldehyde (1.34 g, 10
mmol), trimethyl orthoformate (1.38 g, 13 mmol), and
p-toluenesulfonic acid (19 mg, 0.10 mmol) was stirred
at 70 °C for 3h. Then heated to 140 °C for 12 h, evolved
methanol and trimethyl orthoformate was removed by
distillation take off head. The mixture was distilled un-
der reduced pressure and purified by silica-gel column
chromatography (hexane/ether 10:1) to give 1a [9b]
1-Methoxy-2-phenyl-1-butene (1f) [9d] (E/Z = 1.2:1).
1H NMR (CDCl3, 400 MHz): (E)-isomer; d 1.05 (3H,
t, J = 7.3 Hz), 2.52 (2H, q, J = 7.3 Hz), 3.70 (3H, s),
6.27 (1H, s), 7.15–7.37 (5H, m), (Z)-isomer; d 1.05
(3H, t, J = 7.3 Hz), 2.32 (2H, q, J = 7.3 Hz), 3.63 (3H,
s), 6.08 (1H, s), 7.15–7.37 (3H, m), 7.46–7.50 (2H, m).
1
1-Methoxy-2-phenyl-1-tridecene (1g) (E/Z = 2:1). H
NMR (CDCl3, 400 MHz): (E)-isomer; d 0.92 (3H, t,
J = 6.8 Hz), 1.22–1.46 (18H, m), 2.54 (2H, t, J = 6.8
Hz), 3.71 (3H, s), 6.31 (1H, s), 7.18–7.37 (5H, m), (Z)-
isomer; d 0.92 (3H, t, J = 6.8 Hz), 1.22–1.46 (16H, m),
2.32 (2H, t, J = 6.8 Hz), 3.65 (3H, s), 6.10 (1H, s),
7.18–7.37 (3H, m), 7.48–7.53 (2H, m). 13C NMR
(C6D6, 100 MHz): (E)-isomer; d 14.2, 22.8, 27.0, 28.4–
32.0 (8C), 59.9, 120.3, 125.9 (2C), 126.0, 128.4 (2C),
140.0, 145.3. (Z)-isomer; d 14.2, 22.8, 28.4–32.0 (8C),
32.7, 60.1, 117.0, 126.1, 128.0 (2C), 128.3 (2C), 137.7,
144.1; EI-MS: C20H32O+ requires m/z = 288.2453,
found: 288.2460.
1
(0.90 g, 6.1 mmol, 61%, E/Z = 3.3:1). H NMR (C6D6,
400 MHz): (E)-isomer; d 2.04 (3H, s), 3.11 (3H, s),
6.17 (1H, s), 7.00–7.25 (5H, m), (Z)-isomer; d 1.76
(3H, s), 3.03 (3H, s), 5.72 (1H, s), 7.00–7.25 (3H, m),
7.73–7.77 (2H, m).
The substrates 1b–h were prepared from correspond-
ing ketones by Wittig reaction [1b].
1-Methoxy-2-(p-methoxyphenyl)propene (1b) (E/Z =
1:1.2). 1H NMR (C6D6, 400 MHz): (E)-isomer;
d 2.07 (3H, s), 3.15 (3H, s), 3.30 (3H, s), 6.15 (1H, s),
6.75–6.79 (2H, m), 7.12–7.17 (2H, m), (Z)-isomer;
d 1.79 (3H, s), 3.08 (3H, s), 3.27 (3H, s), 5.73 (1H, s),
6.83–6.87 (2H, m), 7.71–7.74 (2H, m). 13C NMR
(C6D6, 100 MHz): (E)-isomer; d 12.9, 54.5, 59.0, 113.9
(2C), 114.0, 126.1(2C), 133.3, 144.2, 158.4, (Z)-isomer;
1-Methoxy-2,2-diphenylethene (1h) [9e]. 1H NMR
(CDCl3, 400 MHz): d 3.19 (3H, s), 6.25 (1H, s), 7.15–
7.37 (8H, m), 7.70–7.71 (2H, m).
The substrate 1i was prepared from 2-phenylpropion-
aldehyde and 1-dodecanol by a similar procedure to 1a.
1-Dodecyloxy-2-phenylpropene (1i) (E/Z = 5:1). 1H
NMR (CDCl3, 400 MHz): (E)-isomer; d 0.87 (3H, t,
J = 7.2 Hz), 1.20–1.45 (18H, m), 1.62–1.72 (2H, m),
2.00 (3H, s), 3.84 (2H, t, J = 6.8 Hz), 6.47 (1H, s),
7.13–7.35 (5H, m), (Z)-isomer; d 0.87 (3H, t, J = 7.2
Hz), 1.20–1.45 (18H, m), 1.62–1.72 (2H, m), 1.91 (3H,
s), 3.81 (2H, t, J = 6.8 Hz), 6.18 (1H, s), 7.25–7.35
(3H, m), 7.63–7.67 (2H, m), 13C NMR (CDCl3, 100
d 18.2, 54.4, 59.2, 110.2, 113.4 (2C), 128.9 (2C), 131.2,
+
143.7, 158.1; EI-MS: C11H14O2
178.0994, found: 178.0991.
requires m/z =
1-Methoxy-2-(p-tolyl)propene (1c) [9c] (E/Z = 1:1.2).
1H NMR (CDCl3, 400 MHz): (E)-isomer; d 1.98 (3H,
s), 2.34 (3H, s), 3.71 (3H, s), 6.38 (1H, s), 7.08–7.15
(4H, m), (Z)-isomer; d 1.90 (3H, s), 2.34 (3H, s), 3.66
(3H, s), 6.08 (1H, s), 7.18–7.21 (2H, m), 7.48–7.74
(2H, m).