Thermal and photochemical reactions of Fischer carbene complexes with trialkylsilyl-substituted alkynes

Article abstract of DOI:10.1016/j.jorganchem.2007.11.007

Thermal reaction of Fischer carbene complexes with triisopropylsilyl (TIPS) substituted alkynes in benzene afforded TIPS-substituted vinylketenes or 2-TIPS-substituted cyclobutenones as major products while photochemical reaction of Fischer carbene comple

Full text of DOI:10.1016/j.jorganchem.2007.11.007

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Journal of Organometallic Chemistry 693 (2008) 361–367
www.elsevier.com/locate/jorganchem
Note
Thermal and photochemical reactions of Fischer carbene
complexes with trialkylsilyl-substituted alkynes
a
b
a
a
a,
*
Zhi Li , William H. Moser , Wenqin Zhang , Changhua Hua , Liangdong Sun
a
Department of Chemistry, School of Science, Tianjin University, Tianjin 300072, People’s Republic of China
b
Department of Chemistry, Indiana University-Purdue University Indianapolis, Indianapolis, IN, USA
Received 30 September 2007; received in revised form 1 November 2007; accepted 6 November 2007
Available online 13 November 2007
Abstract
Thermal reaction of Fischer carbene complexes with triisopropylsilyl (TIPS) substituted alkynes in benzene afforded TIPS-substituted
vinylketenes or 2-TIPS-substituted cyclobutenones as major products while photochemical reaction of Fischer carbene complexes with
trimethylsilyl (TMS) substituted alkynes in acetonitrile afforded 3-TMS-substituted cyclobutenones.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Fischer carbene; Silyl vinylketene; Cyclobutenone
1. Introduction
photolytic reaction of chromium imine–carbene complexes
with alkynes results in 2H-pyrrole derivatives [7]. However,
the photochemical [2+2] reaction of Fischer carbene com-
plexes with alkynes has not yet been explored. We reported
herein for the first time the photochemical [2+2] reaction of
the Fischer carbene complexes with trialkylsilyl-substituted
alkynes.
The thermal benzannulation of Fischer carbene com-
plexes with alkynes, commonly known as the Do¨tz reac-
tion, have been extensively studied and widely utilized to
generate substituted aromatic ring systems [1]. Recently,
Moser have discovered the interrupted Do¨tz benzannula-
tion of Fischer carbene complexes with trialkylsilyl-substi-
tuted alkynes afforded silyl vinylketenes [2] which can
function as versatile four-carbon building blocks in synthe-
sis of highly substituted carbocyclic and heterocyclic
compounds via [4+1] [2a,3] and [4+2] [4] annulations.
However, the scope of the thermal reaction of Fischer car-
bene complexes with trialkylsilyl-substituted alkynes has
not been extensively studied. On the other hand, the photo-
chemistry of Fischer carbene complexes has experienced an
enormous development in the past decades and the photo-
chemical reactions of Fischer carbene complexes with
imine, alkene, diene, ketone and aldehyde have been well
documented [5]. Low-temperature photolysis of [W(CO)5-
{C(OMe)Ph}] in the presence of alkynes leads to spectro-
scopically observable alkyne–carbene adducts [6] and
2. Results and discussion
2.1. Thermal reaction of Fischer carbene complexes with
TIPS-substituted alkynes
The Fischer carbene complexes 1a–d were prepared
according to the literature [8a]. The initial investigation
of the thermal reaction of Fischer carbene complexes 1a–
d with TIPS-substituted alkynes bearing a phenyl ring
was indicated in Fig. 1.
The degassed solution of Fischer carbene complexes
1a–c and various TIPS-substituted alkynes containing a
phenyl group in benzene was heated at reflux under argon
for 24 h affording the TIPS-vinylketenes complexed with
Cr(CO)3 moiety (Table 1, entries 1–3) or the Cr(CO)3 free
TIPS-vinylketenes (Table 1, entries 4 and 5) in moderate to
good yield [8b].
*
Corresponding author. Tel.: +86 22 81583683; fax: +86 22 27403475.
E-mail address: ldsun@tju.edu.cn (L. Sun).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.11.007

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Z. Li et al. / Journal of Organometallic Chemistry 693 (2008) 361–367
Fig. 1. Thermal reaction of Fischer carbene complexes with TIPS-substituted alkynes containing a phenyl ring.
Table 1
Thermal reaction of 1a–d with TIPS-substituted alkynes
Entry
1
Carbene complex
Alkyne
Product
Yielda [%]
48
1a
O
TIPS
C
MeO
TIPS
Ph
(CO)3Cr
MeO
OMe
3a
2
3
4
5
6
1b
1a
1c
1a
1d
33
TIPS
O
TIPS
C
n
-Bu
(CO)3Cr
OMe
3b
60
O
O
TIPS
O
C
TIPS
Ph
(CO)3Cr
OMe
3c
59
TIPS
O
TIPS
O
C
O
O
Me
OMe
3d
65
O
C
TIPS
TIPS
O
Ph
OMe
3e
O
3f: 32 4a: 30
TIPS
O
TIPS
C
TIPS
+
OCH3
(CO)3Cr
TIPS
(CO)3Cr
OCH3
4a
3f
7
8
1c
1b
66
73
O
TIPS
OMe
Me
4b
TIPS
O
TIPS
O
OMe
-Bu
n
O
4c
a
Isolated yield.

Z. Li et al. / Journal of Organometallic Chemistry 693 (2008) 361–367
363
Interestingly, when the cyclopropyl methoxy chromium
Fischer carbene complex 1d reacted with TIPS-substituted
phenyl acetylene under the same thermal reaction condi-
tions, TIPS vinylketene 3f was obtained in 32% yield along
with 30% of the 2-TIPS-substituted cyclobutenone 4a
(Table 1, entry 6).
Due to the significance of cyclobutenones in organic
chemistry [9] and encouraged by the previous results, we
investigated the thermal reaction of the Fischer carbene
complexes with TIPS-substituted alkynes without a phenyl
group to explore the scope of the interrupted Do¨tz benz-
annulation. Surprisingly, Fischer carbene complex 1c and
1b reacted with TIPS-substituted cyclopropyl acetylene
and TIPS-substituted furan-2-yl acetylene afforded
2-TIPS-substituted cyclobutenone 4b and 4c as sole prod-
uct respectively(Table 1, entries 7 and 8). The regiochemist-
ry of cyclobutenones 4a, 4b and 4c could be established by
the NOE enhancement between the cyclopropyl methylene
proton and the methyl group on the cyclobutenone ring of
4b.
intermediate 7 generates the g4-vinylketene complexed
intermediate 8 [2a,10–12]. The cyclobutenone 4 is formed
from ring closure of the Cr(CO)3 complexed intermediate
8 [1a].
2.2. Photochemical reaction of Fischer carbene complexes
with TMS-substituted alkynes
Initially, Fischer carbene complex 1a was irradiated in
the presence of tert-butyl dimethylsilyl (TBS) or TIPS-
substituted phenyl acetylene under argon. Disappointingly,
the reaction only led to decomposition of 1a. When the
alkyne was switched to phenyl acetylene, the similar disap-
pointing result was observed. While 1a was photolyzed in
the presence of TMS-substituted phenyl acetylene in DME
under argon, a new product 9a was obtained in 10% yield
(see Fig. 3). According to the IR spectra of 9a, the silyl vinyl-
ketene structure was excluded because 9a did not have the
characteristic ketene band at 2080 cmÀ1
.
As shown in Table 2, a variety of reaction conditions
were screened to maximize the cyclobutenone 9a forma-
tion. Photolysis of 1a in the presence of TMS-substituted
phenyl acetylene in benzene or ethyl acetate, disappoint-
ingly, gave none of the desired product (Table 2, entries 2
and 3). A variety of other solvents were screened (Table
2, entries 4–7), but the desired product was obtained in
The proposed mechanism accounted for the thermal
reaction of Fischer carbene complexes with TIPS-substi-
tuted alkynes was outlined in Fig. 2.
Decarbonylation of Fischer carbene complex 1 followed
by coordination of the TIPS-substituted alkyne 2 forms the
alkyne–carbene complex intermediate 5. Subsequent
alkyne insertion of 5 results in the metallacycle intermedi-
ate 6, which undergoes ring opening to generate the inter-
mediate 7 [10]. When the R2 contains a phenyl group,
CO insertion of 7 results in silyl vinylketene 3A with the
Cr(CO)3 moiety coordinated to the phenyl ring. The
Cr(CO)3 moiety in 3A can be removed through ligand
exchange with the benzene solvent to afford 3B [2]. When
the R2 does not contain a phenyl group, CO insertion of
Fig. 3. Photochemical reaction of 1a with TMS-substituted alkyne.
Fig. 2. Proposed mechanism for the thermal reaction of Fischer carbene complexes with TIPS-substituted alkynes.

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Z. Li et al. / Journal of Organometallic Chemistry 693 (2008) 361–367
Table 2
Photolysis of 1a to 9a under different reaction conditions
Entry
Solvent
Adduct
Yield of 9aa [%]
1
2
3
DME
Ethyl acetate
Benzene
10
0
0
4
5
6
7
8
9
10
11
12
a
Dioxane
n-Hexane
Trifluoromethyl benzene
Acetonitrile/dioxane = 1:2
Diethyl ether
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
18
15
13
18
39
43
28
15
28
Fig. 6. [2+2] reaction of TMS-substituted hexyne and carbene complex
1e.
[5b,14]. Excitation into this state results in the formation
of the metalacycle intermediate 10 or the chromium–ketene
complex 11 [5b,14a,14b]. The metal–ketene complex 11
undergoes [2+2] cyclization to afford the cyclobutenone
9a in a similar way to the photochemical [2+2] reaction
of Fischer carbene complexes with olefins [5b,15]. The silyl
group which can enhance the electron density of the alkyne
is necessary because the alkyne serves as the nucleophilic
part in the photochemical [2+2] reaction with the metal–
ketene complex 11 [16]. The similar result was observed
in the photochemical [2+2] cyclization of Fischer carbene
complexes with olefins where the electron-rich olefins
underwent the [2+2] reaction smoothly while the elec-
tron-poor olefins did not give the cyclobutanone product
[15e]. On the other hand, the steric hindrance of the bulky
TBS group may prevent the [2+2] cyclization to give the
cyclobutenone product. This could account for the failure
of the reaction of 1a with phenyl acetylene or TBS-substi-
tuted phenyl acetylene.
PPh3
CuBr
CF3SO3Cu
Isolated yield.
low yield. While the photochemical reaction was carried
out in acetonitrile, the best yield of 9a (43%) was obtained
in all solvents screened. Adducts such as PPh3, CuBr and
CF3SO3Cu in acetonitrile (Table 2, entries 10–12), to our
surprise, lowered the yield.
Similarly, 9b was obtained in 46% in acetonitrile from 1a
and TMS-substituted hexyne (Fig. 4).
The regiochemistry of above two cyclobutenones was
confirmed by transformation of 9b to a known compound
[13]. To our surprise, they are 3-TMS-substituted cyclob-
utenones, in which the regiochemistry was different and
complementary to the 2-TIPS-substituted cyclobutenone
obtained from the thermal reaction.
The mechanism of this 3-TMS-substituted cyclobute-
none-forming reaction is unknown at present. The plausi-
ble mechanism is shown in Fig. 5.
Interestingly, when the carbene complex 1e was stirred
in the presence of TMS-substituted hexyne in acetonitrile
under argon at room temperature for 20 h, 3-TMS-substi-
tuted cyclobutenone 9a was also obtained in 20% yield
(see Fig. 6).
The Fischer carbene complex 1a is initially irradiated
into the metal-to-ligand charge transfer (MLCT) state
3. Conclusions
The thermal and the photochemical reactions of Fischer
carbene complexes with trialkylsilyl-substituted alkynes
were investigated in this paper. In the thermal reaction of
Fischer carbene complexes with TIPS-substituted alkynes,
the silyl vinylketenes generated smoothly when the TIPS-
substituted alkynes contained a phenyl ring. On the con-
trary, 2-TIPS-substituted cyclobutenones could be
obtained if the TIPS-substituted alkynes did not bear a
phenyl group. Finally, the photochemical [2+2] reaction
of the Fischer carbene complexes with the TMS-substituted
alkynes in acetonitrile afforded the 3-TMS-substituted
cyclobutenones.
Fig. 4. Photochemical reaction of 1a with TMS-substituted hexyne.
4. Experimental
4.1. General information
1H NMR spectra and 13C NMR spectra were recorded
on VARIAN INOVA (500 MHz) spectrometer. Chemical
shifts were reported in ppm relative to (CH3)4Si (0 ppm,
Fig. 5. Proposed mechanism for photochemical reaction of Fischer
carbene complexes with TMS-substituted alkynes.

Z. Li et al. / Journal of Organometallic Chemistry 693 (2008) 361–367
365
1H) or CDCl3 (77.0 ppm, 13C). IR spectra were recorded on
1636, 1598, 1461, 1420, 1256, 1158, 1105, 1073, 997 cmÀ1
.
1
Thermo Nicolet AVATAR 360 spectrometer. Mass spectra
were recorded on Bruker Daltonics Inc., APEX II FT-
ICRMS (FAB). Glassware was dried in oven overnight
then flame dried prior to use. Thin layer chromatography
(TLC) was performed on Silica Gel 60 F254 plates and
visualized with UV light and KMnO4 stain. Reactions were
conducted under argon atmosphere unless otherwise noted.
Benzene was distilled from calcium hydride prior to use.
500 MHz H NMR (CDCl3): d 7.40 (5H), 5.43–5.39 (m,
4H), 5.26 (1H), 4.33 (s, 2H), 4.25 (s, 2H), 3.34 (s, 3H),
1.09–0.93 (m, 21H). 125 MHz 13C NMR (CDCl3): d
232.9, 180.4, 157.0, 134.4, 129.9, 128.9, 128.3, 108.3,
108.2, 93.1, 92.9, 92.7, 91.6, 70.4, 69.7, 58.0, 18.6, 12.7,
12.2. HRMS (FAB): m/z calc. for [C31H38CrO6Si+Na]+:
609.1740. Found: 609.1746.
4.2.4. Silyl vinylketene 3d
4.2. General procedure for thermal reactions of Fischer
carbene complexes with TIPS-substituted alkynes
Carbene complex (250 mg, 1.0 mmol) and alkyne
(520 mg, 1.8 mmol) were subjected to the general proce-
dure, affording silyl vinylketene 3d (219 mg, 59% yield) as
a colorless oil. IR (neat): m 2944, 2866, 2085, 1647, 1598,
1585, 1495, 1463, 1381, 1299, 1235, 1154, 1075, 1029,
1006, 939, 882 cmÀ1. 500 MHz 1H NMR (CDCl3): d
7.26–7.23 (m, 2H), 6.93–6.89 (m, 3H), 4.60 (s, 2H), 3.58
(s, 3H), 2.05 (s, 3H), 1.21–1.13 (m, 3H), 1.09–1.08 (m,
18H). 125 MHz 13C NMR (CDCl3): d 179.0, 158.7, 154.4,
129.2, 120.3, 114.9, 104.8, 65.5, 56.3, 18.5, 14.8, 12.6,
11.3. HRMS (FAB): m/z calc. for [C22H34O3Si+Na]+:
397.2175. Found: 397.2170.
A degassed solution of the appropriate Fischer carbene
complex (1.0 equiv.) and silyl-substituted alkyne (1.8
equiv.) in benzene was heated at reflux under argon atmo-
sphere for 24 h. Upon cooling to room temperature, the
solution was concentrated under reduced pressure, and
the residue was purified via flash chromatography (SiO2,
30:1 petroleum ether/ethyl acetate) to afford the silyl vinyl-
ketenes or the cyclobutenones.
4.2.1. Silyl vinylketene 3a
Carbene complex (312 mg, 1.0 mmol) and alkyne
(514 mg, 1.8 mmol) were subjected to the general procedure,
affording silyl vinylketene 3a (272 mg, 48% yield). IR (neat):
m 2946, 2867, 2084, 1959, 1877, 1741, 1593, 1539, 1462, 1252,
1124 cmÀ1. 500 MHz 1H NMR (CDCl3): d 7.41–7.37
(m, 3H), 7.33–7.32 (m, 2H), 6.07 (d, J = 7.0 Hz, 2H), 5.21
(d, J = 7.0 Hz, 2H), 3.73 (s, 3H), 3.37 (s, 3H), 0.88–0.79
(m, 21H). 125 MHz 13C NMR (CDCl3): d 234.0, 180.1,
157.9, 141.2, 135.0, 129.8, 129.1, 128.5, 103.9, 102.9, 97.0,
78.4, 58.0, 55.9, 18.5, 14.6, 12.5. HRMS (FAB): m/z calc.
for C30H36CrO6Si: 572.1686. Found: 572.1683.
4.2.5. Silyl vinylketene 3e
Carbene complex (312 mg, 1.0 mmol) and alkyne
(520 mg, 1.8 mmol) were subjected to the general proce-
dure, affording silyl vinylketene 3e (283 mg, 65% yield) as
a colorless oil. IR (neat): m 2944, 2866, 2085, 1598, 1494,
1462, 1287, 1238, 1170, 1107, 1074, 1030, 1003, 881 cmÀ1
.
500 MHz1H NMR (CDCl3): d 7.41–7.33 (m, 5H), 7.30–
7.27 (m, 2H), 7.00 (dd, J = 8.5 Hz, J = 1.0 Hz, 2H), 6.94
(t, J = 7.5 Hz, 1H), 4.78 (s, 2H), 3.35 (s, 3H), 0.91–0.89
(m, 21H). 125 MHz 13C NMR (CDCl3): d 179.7, 158.7,
156.5, 134.1, 129.8, 129.3, 128.6, 128.5, 128.0, 120.6,
115.0, 107.6, 66.6, 57.7, 18.5, 12.2, 11.7. HRMS (FAB):
m/z calc. for C27H36O3Si: 436.2434. Found: 436.2431.
4.2.2. Silyl vinylketene 3b
Carbene complex (280 mg, 1.0 mmol) and alkyne
(403 mg, 1.8 mmol) were subjected to the general proce-
dure, affording silyl vinylketene 3b (180 mg, 33% yield) as
a yellow oil. IR (neat): m 2951, 2867, 2080, 1964, 1889,
1739, 1596, 1525, 1460, 1382, 1307, 1257, 1211, 1156,
4.2.6. Silyl vinylketene 3f and cyclobutenone 4a
Carbene complex (276 mg, 1.0 mmol) and alkyne
(464 mg, 1.8 mmol) were subjected to the general proce-
dure, affording silyl vinylketene 3f (162 mg, 32% yield).
1064, 973, 879, 804 cmÀ1. 500 MHz H NMR (CDCl3): d
IR (neat): m 2084, 1963, 1887 cmÀ1. 300 MHz H NMR
1
1
7.33 (d, J = 16.0 Hz, 1H), 6.16 (d, J = 15.5 Hz, 1H),
5.55–5.54 (m, 2H) 5.32–5.31 (m, 3H), 3.63 (s, 3H), 2.54
(t, J = 8.0 Hz, 2H), 1.50–1.47 (m, 2H), 1.40–1.36 (m, 2H),
1.26–1.21 (m, 3H), 1.15–1.11 (m, 18H), 0.95 (t, J =
7.5 Hz, 3H). 125 MHz 13C NMR (CDCl3): d 233.3, 177.8,
160.8, 129.2, 128.4, 128.2, 124.5, 109.2, 107.0, 92.4, 92.0,
91.8, 56.8, 29.7, 29.0, 23.0, 18.8, 14.1, 13.0, 9.4. HRMS
(FAB): m/z calc. for C29H40CrO5Si: 548.2050. Found:
548.2043.
(CDCl3): 5.79–5.77 (m, 2H), 5.27–5.25 (m, 3H), 3.62 (s,
3H), 1.81–1.76 (m, 1H), 1.17–1.07 (m, 21H), 0.96–0.88
(m, 2H), 0.80–0.75 (m, 2H). 75.5 MHz 13C NMR (CDCl3):
233.4, 178.4, 159.9, 110.5, 107.1, 95.7, 91.9, 57.8, 18.7, 13.8,
1
12.9, 12.8, 7.6. The H and 13C NMR data consistent with
the literature [2a] and the cyclobutenone 4a (152 mg, 30%
yield). IR (neat): m 2945, 2866, 1973, 1903, 1739, 1542,
1456, 1070, 882 cmÀ1. 300 MHz 1H NMR (CDCl3): d
6.14–6.04 (m, 1H), 5.93–5.82 (m, 1H), 5.72–5.58 (m, 1H),
5.35–5.21 (m, 2H), 3.44 (s, 3H), 1.54–1.29 (m, 4H), 1.23–
1.00 (m, 18H), 0.97–0.82 (m, 2H), 0.76–0.64 (m, 2H).
75.5 MHz 13C NMR (CDCl3): d 230.8, 196.0, 184.0,
152.1, 102.0, 95.1, 94.9, 94.5, 92.6, 88.5, 88.3, 53.1, 18.8,
18.7, 14.6, 12.0, 4.0, 3.0. HRMS (FAB): m/z calc. for
C26H34CrO5Si: 506.1581. Found: 506.1589.
4.2.3. Silyl vinylketene 3c
Carbene complex (312 mg, 1.0 mmol) and alkyne
(540 mg, 1.8 mmol) were subjected to the general proce-
dure, affording silyl vinylketene 3c (351 mg, 60% yield) as
a yellow oil. IR (neat): m 2944, 2866, 2082 1971, 1893,

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Z. Li et al. / Journal of Organometallic Chemistry 693 (2008) 361–367
4.2.7. Cyclobutenone 4b
in 15 ml acetonitrile was irradiated under argon for 24 h.
After filtered via Celite, the solution was concentrated
under reduced pressure and purified via flash chromatogra-
phy (SiO2, 30:1 petroleum ether/ethyl acetate) to afford the
cyclobutenone 9b (174 mg, 46% yield) as a yellowish oil. IR
(neat): m 2957, 2934, 2873, 2830, 1750, 1493, 1449, 1251,
1197, 1135, 1078, 1019, 843 cmÀ1. 500 MHz 1H NMR
(CDCl3): d 7.34–7.20 (m, 5H), 3.45 (s, 3H), 2.45–2.31 (m,
2H), 1.71–1.54 (m, 2H), 1.48–1.29 (m, 2H), 0.92 (t,
J = 7.0 Hz, 3H), 0.15 (s, 9H). 125 MHz 13C NMR
(CDCl3): d 193.6, 184.1, 169.3, 138.8, 128.1, 127.6, 125.8,
103.7, 52.9, 29.9, 25.8, 22.8, 13.7, À1.3. HRMS (FAB):
m/z calc. for C18H26O2Si: 302.1702. Found: 302.1709.
Carbene complex (250 mg, 1.0 mmol) and alkyne
(400 mg, 1.8 mmol) were subjected to the general proce-
dure, affording cyclobutenone 4b (203 mg, 66% yield). IR
(neat): m 2942, 2865, 1740, 1554, 1459, 1368, 1303, 1234,
1124, 1093, 1063 cmÀ1. 500 MHz 1H NMR (CDCl3): d
3.27 (s, 3H), 2.09–2.04 (m, 1H), 1.38 (s, 3H), 1.37–1.30
(m, 4H), 1.23–1.18 (m, 3H), 1.11–1.09 (m, 18H).
125 MHz 13C NMR (CDCl3): d 198.6, 151.0, 97.9, 52.5,
21.1, 18.6, 18.5, 15.2, 11.2, 10.7, 9.9. HRMS (FAB): m/z
calc. for C18H32O2Si: 308.2172. Found: 308.2165.
4.2.8. Cyclobutenone 4c
Carbene complex (215 mg, 0.73 mmol) and alkyne
(340 mg, 1.3 mmol) were subjected to the general procedure,
affording cyclobutenone 4c (201 mg, 73% yield). IR (neat): m
2931, 2865, 1748, 1600, 1516, 1455, 1388, 1300, 1125, 1084,
4.4. Reaction of 1e with TMS-substituted hexyne at room
temperature
1
1021 cmÀ1. 500 MHz H NMR (CDCl3): d 7.74–7.73 (m,
A degassed solution of the Fischer carbene complex 1e
(480 mg, 0.88 mmol) and the alkyne (271 mg, 1.76 mmol)
in 10 ml acetonitrile was stirred at room temperature under
argon for 20 h. After filtered via Celite, the solution was
concentrated under reduced pressure and purified via flash
chromatography (SiO2, 30:1 petroleum ether/ethyl acetate)
to afford the cyclobutenone 9a (55 mg, 20% yield).
1H), 7.05–7.04 (m, 1H), 6.62–6.61 (m, 1H), 3.25 (s, 3H),
2.02–1.96 (m, 1H), 1.86–1.80 (m, 1H), 1.56–1.49 (m, 3H),
1.30–1.25 (m, 4H), 1.08 (d, J = 7.5 Hz, 18H), 0.82
(t, J = 7.0 Hz, 3H). 125 MHz 13C NMR (CDCl3): d 198.4,
172.4, 148.2, 148.1, 146.9, 118.3, 113.6, 102.7, 53.1, 33.4,
28.2, 23.6, 19.3, 14.4, 12.0. HRMS (FAB): m/z calc. for
C22H36O3Si: 376.2434. Found: 376.2428.
Acknowledgements
4.3. General procedure for photochemical reactions of
Fischer carbene complexes with TMS-substituted alkynes
This work was supported by National Natural Science
Foundation of China (20402010). We thank State Key
Laboratory of Elemento-organic Chemistry, Nankai Uni-
versity for the support.
A degassed solution of the appropriate Fischer carbene
complex (1.0 equiv.) and silyl-substituted alkyne (2.0 equiv.)
in acetonitrile in a quartz tube charged with glass beads was
irradiated with a 20-W Vitalite under argon at room temper-
ature for 24 h. The red solution turned light-yellow and
heterogeneous. After filtered through a bed of Celite, the
solution was concentrated under reduced pressure and
purified via flash chromatography (SiO2, 30:1 petroleum
ether/ethyl acetate) to afford the cyclobutenone.
References
[1] For reviews of the Do¨tz benzannulation see: (a) K.H. Do¨tz, P.
Tomuschat, Chem. Soc. Rev. 28 (1999) 187;
(b) W.D. Wulff, in: A.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.),
Comprehensive Organometallic Chemistry II, vol. 12, Pergamon,
Oxford, 1995;
(c) L.S. Hegedus, in: A.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.),
Comprehensive Organometallic Chemistry II, vol. 12, Pergamon,
Oxford, 1995;
4.3.1. Cyclobutenone 9a
A degassed solution of the Fischer carbene complex
(390 mg, 1.25 mmol) and the alkyne (375mg, 2.50 mmol)
in 15 ml acetonitrile was irradiated under argon for 24 h.
After filtered via Celite, the solution was concentrated
under reduced pressure and purified via flash chromatogra-
phy (SiO2, 30:1 petroleum ether/ethyl acetate) to afford the
(d) D.F. Harvey, D.M. Sigano, Chem. Rev. 96 (1996) 271.
[2] (a) W.H. Moser, L.A. Feltes, L. Sun, M.W. Giese, R.W. Farrell, J.
Org. Chem. 71 (2006) 6542;
(b) W.H. Moser, L. Sun, J.C. Huffman, Org. Lett. 3 (2001) 3389.
[3] (a) C.P. Davie, R.L. Danheiser, Angew. Chem., Int. Ed. 44 (2005)
5867;
1
(b) J.H. Rigby, Z. Wang, Org. Lett. 5 (2003) 263;
(c) A.M. Dalton, Y. Zhang, C.P. Davie, R.L. Danheiser, Org. Lett. 4
(2002) 2465;
(d) J.L. Loebach, D.M. Bennett, R.L. Danheiser, J. Am. Chem. Soc.
120 (1998) 9690.
cyclobutenone 9a (173 mg, 43% yield). 500 MHz H NMR
(CDCl3): d 7.83–7.81 (m, 2H), 7.48–7.42 (m, 5H), 7.35–7.31
(m, 2H), 7.28–7.23 (m, 1H), 3.52 (s, 3H), 0.25 (s, 9H).
125 MHz 13C NMR (CDCl3): d 192.0, 181.8, 162.9,
138.9, 130.3, 129.9, 129.0, 128.6, 128.5, 128.0, 126.2,
104.3, 53.3, À1.2. HRMS (FAB): m/z calc. for C20H22O2Si:
322.1389. Found: 322.1387.
[4] (a) W.F. Austin, Y. Zhang, R.L. Danheiser, Org. Lett. 7 (2005) 3905;
(b) D.M. Bennett, I. Okamoto, R.L. Danheiser, Org. Lett. 1 (1999)
641;
(c) J.L. Loebach, D.M. Bennett, R.L. Danheiser, J. Org. Chem. 63
(1998) 8380;
(d) R.L. Danheiser, H. Sard, J. Org. Chem. 45 (1980) 4810.
[5] For reviews see: (a) L.S. Hegedus, Top. Organomet. Chem. 13 (2004)
157;
4.3.2. Cyclobutenone 9b
A degassed solution of the Fischer carbene complex
(390 mg, 1.25 mmol) and the alkyne (385 mg, 2.50 mmol)

Z. Li et al. / Journal of Organometallic Chemistry 693 (2008) 361–367
367
(b) L.S. Hegedus, Tetrahedron 53 (1997) 4105;
(c) L.S. Hegedus, in: E.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.),
Comprehensive Organometallic Chemistry II, vol. 12, Pergamon,
Oxford, 1995, pp. 549–576.
[12] For examples of g4-vinyl ketene complexes isolated from reactions of
metal carbene complex with alkyne see: (a) W.D. Wulff, S.R.
Gilbertson, J.P. Springer, J. Am. Chem. Soc. 108 (1986) 520;
(b) M.F. Semmelhack, R. Tamura, W. Schnatter, J. Park, M.
Steigerwald, S. Ho, New Aspects of Organic Chemistry, in: Proceed-
ings of the Third International Kyoto Conference on Organic
Chemistry, Kyoto, Japan, March, 1986, Kodansha Ltd., Tokyo,
Japan.
[6] H.C. Foley, L.M. Strubinger, T.S. Targos, G.L. Geoffroy, J. Am.
Chem. Soc. 105 (1983) 3064.
´
[7] P.J. Campos, D. Sampedro, M.A. Rodrıguez, J. Org. Chem. 68
(2003) 4674.
[8] (a) L.S. Hegedus, M.A. McGuire, L.M. Schultze, Org. Synth. 8
(1993) 216;
[13] A degassed solution of 9b in toluene was heated at reflux under argon
for 16 h to give 2-butyl-3-TMS-4-methoxy naphthalen-1-ol in 64%
yield. 2-Butyl-3-TMS-4-methoxy naphthalen-1-ol was treated with
TFA in CHCl3 at room temperature affording the 2-butyl-4-methoxy
naphthalen-1-ol in 46% yield with 1H and 13C NMR data consistent
with the literature: A. Yamashita, R.G. Schaub, M.K. Bach, G.J.
White, A. Toy, et al., J. Med. Chem. 33 (1990) 775.
[14] (a) M.L. Gallagher, J.B. Greene, A.D. Rooney, Organometallics 16
(1997) 5260;
(b) Thermal reactions of Fischer carbene complexes with TMS-
substituted alkynes only afforded normal Do¨tz annulation products
instead of silyl vinylketenes in refluxing benzene.
[9] For the recent developments of cyclobutenones in organic synthesis
see: (a) D.C. Harrowven, D.D. Pascoe, I.L. Guy, Angew. Chem., Int.
Ed. 46 (2007) 425;
(b) T. Kondo, M. Niimi, M. Nomura, K. Wada, T. Mitsudo,
Tetrahedron Lett. 48 (2007) 2837;
(c) T. Kondo, Y. Taguchi, Y. Kaneko, M. Niimi, T. Mitsudo,
Angew. Chem., Int. Ed 43 (2004) 5369;
(d) N.A. Magomedov, P.L. Ruggiero, Y. Tang, J. Am. Chem. Soc.
126 (2004) 1624;
(e) A.R. Hergueta, H.W. Moore, J. Org. Chem. 67 (2002) 1388;
(f) M. Murakami, Y. Miyamoto, Y. Ito, J. Am. Chem. Soc. 123
(2001) 6441;
(b) L.S. Hegedus, G. de Weck, S. D’Andrea, J. Am. Chem. Soc. 110
(1988) 2122;
(c) L.S. Hegedus, M.A. McGuire, L.M. Schultze, C. Yijun, O.P.
Anderson, J. Am. Chem. Soc. 106 (1984) 2680;
(d) L.S. Hegedus, M.A. McGuire, J. Am. Chem. Soc. 104 (1982)
5538.
[15] (a) L.S. Hegedus, R.W. Bates, B.C. So¨derberg, J. Am. Chem. Soc.
113 (1991) 923;
(g) M. Zora, I. Koyuncu, B. Yucel, Tetrahedron Lett. 41 (2000) 7111.
[10] (a) H. Fischer, J. Mulheimer, R. Markl, K.H. Do¨tz, Chem. Ber. 115
(1982) 1355;
(b) L.S. Hegedus, B.C. So¨derberg, J. Org. Chem. 56 (1991) 2209;
(c) B.C. So¨derberg, L.S. Hegedus, M.A. Sierra, J. Am. Chem. Soc.
112 (1990) 4364;
´
`
(b) K.H. Do¨tz, B.F. Koster, Chem. Ber. 113 (1980) 1449.
[11] (a) B.A. Anderson, J. Bao, T.A. Brandvold, C.A. Challener, W.D.
Wulff, Y.C. Xu, A.L. Rheingold, J. Am. Chem. Soc. 115 (1993)
10671;
(d) E. Valentı, M.A. Pericas, A. Moyano, J. Org. Chem. 55 (1990)
3582;
(e) L.S. Hegedus, M.A. Sierra, J. Am. Chem. Soc. 111 (1989) 2335.
[16] Contrary to the bulky TIPS group of alkynes used in thermal
reactions, the relatively small TMS group of alkynes in photochemical
reactions probably could be another factor that would favor the
observed different regiochemistry of 9a and 9b.
(b) L.S. Hegedus, D.B. Miller Jr., J. Org. Chem. 54 (1989) 1241;
(c) J.S. McCallum, F.A. Kunng, S.R. Gilbertson, W.D. Wulff,
Organometallics 7 (1988) 2346.