Synthesis of 2-pyranylidene or (2-furyl)carbene-chromium complexes from conjugated enyne carbonyl compounds with Cr(CO)5(THF)

Article abstract of DOI:10.1016/S0022-328X(01)01328-6

The reaction of Β-ethynyl α,β-unsaturated esters or amides with Cr(CO)₅(L) (L = Et₂O, THF), derived from chromium hexacarbonyl, gives 2-pyranylidene-chromium complexes in good yields. The conjugated ene-carbonyl-vinylidene complex is a key intermediate to these Fischer-type oxacarbene complexes. In contrast, β-ethynyl α,β-unsaturated ketones react with Cr(CO)₅(THF) to give (2-furyl)carbene complexes via nucleophilic attack of the carbonyl oxygen atom to the intermediate π-alkyne-chromium complexes. Some chemical transformation, such as [4 + 2] type cyclization of 2-pyranylidene complexes with alkynes and aldehyde formation from (2-furyl)carbene complexes, has also been described.

Full text of DOI:10.1016/S0022-328X(01)01328-6

Journal of Organometallic Chemistry 645 (2002) 228–234
www.elsevier.com/locate/jorganchem
Synthesis of 2-pyranylidene or (2-furyl)carbene–chromium
complexes from conjugated enyne carbonyl compounds with
Cr(CO)5(THF)
Koji Miki, Tomomi Yokoi, Fumiaki Nishino, Kouichi Ohe *, Sakae Uemura *
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto Uni6ersity, Sakyo-ku, Kyoto 606-8501, Japan
Received 21 August 2001; received in revised form 18 September 2001; accepted 23 September 2001
Abstract
The reaction of b-ethynyl a,b-unsaturated esters or amides with Cr(CO)5(L) (L=Et2O, THF), derived from chromium
hexacarbonyl, gives 2-pyranylidene–chromium complexes in good yields. The conjugated ene-carbonyl-vinylidene complex is a
key intermediate to these Fischer-type oxacarbene complexes. In contrast, b-ethynyl a,b-unsaturated ketones react with
Cr(CO)5(THF) to give (2-furyl)carbene complexes via nucleophilic attack of the carbonyl oxygen atom to the intermediate
p-alkyne–chromium complexes. Some chemical transformation, such as [4+2] type cyclization of 2-pyranylidene complexes with
alkynes and aldehyde formation from (2-furyl)carbene complexes, has also been described. © 2002 Elsevier Science B.V. All rights
reserved.
Keywords: Chromium; Pyranylidene; Furylcarbene; Vinylidene
of oxacarbene complexes in catalytic and stoichiometric
reactions [3–5]. We have recently reported that 2-
pyranylidene–molybdenum and –tungsten complexes,
as cyclic Fischer-type oxacarbene complexes, were pre-
pared from M(CO)5(L) (M=Mo, W; L=THF, NEt3)
and b-ethynyl a,b-unsaturated esters or amides via nu-
cleophilic attack of the carbonyl oxygen to the a-car-
bon of a vinylidene–metal intermediate (Scheme 1)
[6,7]. However, the preparation of 2-pyranylidene–
chromium complexes from Cr(CO)5(L) (L=Et2O,
THF), which was prepared by photo-irradiation, was
unsuccessful. The complex Cr(CO)5(NMe3) [8] prepared
from Cr(CO)6 and trimethylamine-N-oxide in situ was
only slightly effective for the preparation of 2-pyranyli-
dene–chromium complex. After we investigated the
optimal conditions to obtain 2-pyranylidene–chromium
complexes, we found that the reaction of b-ethynyl
a,b-unsaturated esters or amides with Cr(CO)5(solv),
which was prepared from Cr(CO)6 by irradiation in a
suitable solvent, in the presence of Et3N as an additive
gave effectively the corresponding pyranylidene–
chromium complexes. In sharp contrast with this result,
the reaction of b-ethynyl a,b-unsaturated ketones
with Cr(CO)5(THF) afforded new (2-furyl)carbene–
1. Introduction
Transition metal carbene complexes, especially Fis-
cher-type oxacarbene complexes, have been widely
studied and applied to synthetic organic chemistry as
versatile organometallic reagents [1,2]. Typical oxacar-
bene complexes like (CO)5MꢀC(OR)R% are readily pre-
pared by the reaction of metal hexacarbonyl with a
range of organolithium and organomagnesium
reagents. Nucleophilic addition of an alcohol to the a-
and b-carbons of a vinylidene–metal complex (M=
Ca=Cb, M=Cr, Mo, W) also leads to the formation
Scheme 1.
* Corresponding authors. Tel.: +81-75-753-5687; fax: +81-75-
753-3573.
E-mail address: uemura@scl.kyoto-u.ac.jp (S. Uemura).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01328-6

K. Miki et al. / Journal of Organometallic Chemistry 645 (2002) 228–234
229
Table 1
Preparation of 2a
chromium complexes. The 5-exo-dig nucleophilic cy-
clization in a p-alkyne complex of the ketone with
Cr(CO)5 might be responsible for the formation of
nonstabilized carbene complexes. 2-Pyranylidene–
chromium complexes undergo [4+2] type cycloaddi-
tion with dimethyl acetylenedicarboxylate followed by
demetallation to give tetralin derivatives, while (2-
furyl)carbene–chromium complexes react with molecu-
lar oxygen to give the corresponding furfurals.
Solvent
Additive
Isolated yield (%)
Et2O (30 ml)
Et2O (30 ml)
THF (20 ml)
Et3N (0.1 ml)
Et3N (0.1 ml)
27
62
2. Results and discussion
a The solution of Cr(CO)5(L) was prepared by irradiating Cr(CO)6 (in
Et2O or THF) for 4 h with a high-pressure Hg lamp.
We have reported that 2-pyranylidene–tungsten or
–molybdenum complexes were prepared from b-ethynyl
a,b-unsaturated esters or amides with W(CO)5(THF) [9]
or Mo(CO)5(NEt3) [8]. However, the corresponding
pyranylidene–chromium complexes could not be pre-
pared under similar conditions using Cr(CO)5(Et2O) or
Cr(CO)5(THF). When we examined the reaction with
these chromium complexes in more detail, we found
that the reaction of b-ethynyl a,b-unsaturated ester 1a
with Cr(CO)6 and Me3N+O− gave 2-pyranylidene–
chromium complex 2a in 9% yield (Eq. (1)). We consid-
Table 2
Preparation of pyranylidene–chromium complexes from conjugated
enyne carbonyls and Cr(CO)5(THF) a,b
(1)
ered that trimethylamine, which is generated from the
reaction between Cr(CO)6 and Me3N+O− might play
some role in the formation of pyranylidene complex.
Then we tried the reaction using an amine as an
additive. The reaction of 1a with Cr(CO)5(Et2O) in the
absence of triethylamine gave none of 2a (Table 1).
However, the reaction proceeded in the presence of
triethylamine to give complex 2a in 27% isolated yield
together with the recovered 1a (30–50%). The use of
THF instead of Et2O as a solvent gave a better yield of
2a. The reactions of other substrates with
Cr(CO)5(THF) in the presence of triethylamine were
next examined, typical results of which being shown in
Table 2.
Reactions of 1a with
a
lesser amount of
Cr(CO)5(THF) gave lower yields of 2a in 15% (1.2
equivalents of Cr) and 33% (2.0 equivalents of Cr),
respectively (entries 1 and 2). The reaction of an amide
1b with Cr(CO)5(THF) at room temperature for 0.5 h
also gave the corresponding 2-pyranylidene–chromium
complex 2b in 68% yield (entry 4). The ester 1c and the
amide 1d gave similar complexes 2c and 2d in 69 and
50% yields, respectively (entries 5 and 6). At present, we
assume that triethylamine facilitates the formation of a
vinylidene–chromium intermediate from a p-alkyne–
chromium complex (Scheme 2) [7b].
Scheme 2.

230
K. Miki et al. / Journal of Organometallic Chemistry 645 (2002) 228–234
The structure of pyranylidene–chromium complexes
chromatography. 2-Thienyl ketone 4b also gave the
corresponding (2-furyl)carbene–chromium complex 5b
in 59% yield. When 4a was treated with three equiva-
lents of W(CO)5(THF), (2-furyl)carbene–tungsten com-
plex 5c was isolated in 56% yield [11] (Eq. (4)).
represents a-metallopyrone. Therefore, we envisaged
cycloaddition reaction of these 2-pyranylidene–
chromium complexes with dienophiles. The reaction of
2a with an excess amount of dimethyl acetylenedicar-
boxylate (DMAD, 15 equivalents) gave the tetralin
derivative 3a in 26% isolated yield (Table 3). The use of
solvent, i.e., toluene, did not positively affect the reac-
tion. The reaction in DMSO resulted in demetallation
leading to the formation of compound 1a in 59% yield.
The complex 2b also reacted with DMAD to give the
corresponding tetralin derivative 3b in 25% yield. How-
ever, the reaction of 2a with an electron-rich dienophile,
i.e., ethyl ethynyl ether, gave only a trace amount of
tetralin derivative as one isomer (Eq. (2)). The transfor-
mation was explained by assuming [4+2] cycloaddition
reaction between 2-pyranylidene–chromium complex
and the acetylene followed by a pericyclic demetallation
of chromium hexacarbonyl (Scheme 3).
(3)
(4)
However, in the reaction of an alkyl vinyl ketone, such
as ethyl 2-ethynyl-1-cyclohexenyl ketone (R=Et in 4),
we could not succeed in the isolation of the correspond-
ing (2-furyl)carbene complex. These complexes 5a–5c
were stored for several days under N2 atmosphere, but
they gradually decomposed in CDCl3 or under oxygen
atmosphere. When the isolated carbene complex 5a was
stirred in THF under oxygen atmosphere, furfural
derivative 6a was obtained in 76% yield. The displace-
ment of metal carbonyl moiety with the oxygen atom in
carbene complex by molecular oxygen is a well-known
process [12]. Most plausible pathway from 4 to 5 is
shown in Scheme 4.
(2)
Next, we examined the reactions of b-ethynyl a,b-un-
saturated ketone instead of b-ethynyl a,b-unsaturated
ester or amide with chromium and tungsten carbonyls.
When 2-ethynyl-1-cyclohexenyl phenyl ketone (4a) was
treated with three equivalents of Cr(CO)5(THF) in the
presence of triethylamine, the corresponding 2-pyranyli-
dene–chromium complex 2e was obtained only in 8%
yield together with many unidentified products (Eq.
(3)). On the other hand, in the absence of triethylamine
the reaction of 4a with three equivalents of
Cr(CO)5(THF) did not afford 2e, and instead (2-
furyl)carbene–chromium 5a was isolated in 52% yield
as a blue solid (Eq. (4)) [10]. The complex 5a is mar-
ginally stable during purification with silica gel column
In the pre-equilibrium between a p-alkyne complex 7
and a vinylidene complex 8, 5-exo-dig cyclization takes
place as a favorable process to give the furylcarbene
Table 3
Reaction of pyranylidene–chromium complex with dimethyl acetylene
dicarboxylate
Scheme 3.
Entry
Substrate
Solvent
Product
Yield (%) a
1
2
3
4
5
2a
2b
2a
2a
2a
–
–
3a
3b
3a
3a
3a
26
25
9
Toluene
Dioxane
DMSO
0
0 b
a Isolated yield.
b An enyne carbonyl compound 1a was obtained in 59% yield.
Scheme 4.

K. Miki et al. / Journal of Organometallic Chemistry 645 (2002) 228–234
231
complex. The presence of triethylamine, which may
promote the isomerization of a p-alkyne complex to a
vinylidene complex, in fact, precluded the formation of
the (2-furyl)carbene complex. The mode of the complex
formation is also attributed to the difference in the
reactivity of carbonyl functionality of b-ethynyl a,b-un-
saturated carbonyl compounds.
was subjected to column chromatography on SiO2 with
hexane–EtOAc (v/v=10:1) as an eluent to afford 2a
(44 mg, 62% yield) as an orange solid, m.p. 91.5–
94.3 °C. IR (KBr, cm−1): 1897, 1935, 1976, 2053.
1H-NMR (CDCl3, 300 MHz, 25 °C): l=1.72–1.84 (m,
4H), 2.38–2.49 (m, 2H), 2.55–2.64 (m, 2H), 4.32 (s,
3H), 7.33 (s, 1H). 13C-NMR (CDCl3, 75 MHz, 25 °C):
l=20.4, 21.2, 21.4, 29.0, 56.9, 108.2, 134.7, 154.9,
171.9, 218.6 (CrꢁCO), 223.4 (CrꢁCO), 251.0 (Cr=C).
HRMS (FAB); m/z: 355.9995 ([M+], calc. for
C15H12CrO7: 355.9988).
3. Conclusions
We have demonstrated that 2-pyranylidene–
chromium complexes were prepared from b-ethynyl
a,b-unsaturated esters and amides in the presence of
triethylamine. In sharp contrast, the reaction of b-eth-
ynyl a,b-unsaturated ketones with M(CO)5(THF) (M=
Cr, W) gave (2-furyl)carbene complexes selectively via
nucleophilic attack of a carbonyl oxygen to a p-alkyne
complex. Some chemical transformation of newly pre-
pared 2-pyranylidene–chromium complexes and (2-
furyl)carbene–chromium and tungsten complexes has
been described: [4+2] type cyclization with alkynes in
the former cases and aldehyde formation in the latter
cases, respectively.
4.2.2. 2-Pyranylidene–chromium complex 2b from 1b
An orange solid (68% yield), m.p. 118.4–121.5 °C.
IR (KBr, cm−1): 1888, 1909, 1965, 2045. 1H-NMR
(CDCl3, 300 MHz, 25 °C): l=1.36 (t, J=6.9 Hz, 6H),
1.69–1.79 (m, 4H), 2.44–2.50 (m, 2H), 2.53–2.60 (m,
2H), 3.63 (q, J=6.9 Hz, 4H), 6.96 (s, 1H). 13C-NMR
(CDCl3, 75 MHz, 25 °C): l=13.7, 21.1, 22.6, 25.4,
29.5, 44.7, 108.6, 132.0, 151.2, 170.1, 219.3 (CrꢁCO),
223.9 (CrꢁCO), 240.7 (CrꢀC). Anal. Calc. for
C18H19CrNO6: C, 54.41; H, 4.82; N, 3.53. Found: C,
54.27; H, 5.03; N, 3.40%.
4.2.3. 2-Pyranylidene–chromium complex 2c from 1c
An orange solid (69% yield), m.p. 71.0–73.5 °C. IR
(KBr, cm−1): 1898, 1917, 1976, 2053. 1H-NMR
(CDCl3, 300 MHz, 25 °C): l=4.32 (s, 3H), 6.15 (d,
J=8.1 Hz, 1H), 7.15 (dd, J=8.1, 8.1 Hz, 1H), 7.68 (d,
J=8.1 Hz, 1H). 13C-NMR (CDCl3, 75 MHz, 25 °C):
l=57.0, 96.9, 134.1, 139.6, 175.0, 217.9 (CrꢁCO),
223.4 (CrꢁCO), 269.6 (CrꢀC). HRMS (FAB); m/z:
301.9518 ([M+], calc. for C11H6CrO7: 301.9519).
4. Experimental
4.1. General
Tetrahydrofuran (THF) and Et2O were distilled from
sodium benzophenone ketyl under Ar. Analytical thin-
layer chromatographies (TLC) were performed with
silica gel 60 Merck F-254 plates. Column chromatogra-
phies were performed with Merck silica gel 60. The
NMR spectra were measured for solutions in CDCl3 or
THF-d8 with Me4Si as an internal standard (1H and
13C) and the following abbreviations are used: s, singlet;
d, doublet; t, triplet; q, quartet; quint, quintet; m,
multiplet. IR spectra were recorded with a FT-IR spec-
trometer. Melting points (m.p.) are uncorrected. Ele-
mental analyses were performed at Microanalytical
Center of Kyoto University. All new compounds were
prepared and fully characterized.
4.2.4. 2-Pyranylidene–chromium complex 2d from 1d
An orange solid (50% yield), m.p. 128.3–129.5 °C.
1
IR (KBr, cm−1): 1906, 1966, 2052. H-NMR (CDCl3,
300 MHz, 25 °C): l=3.75–3.87 (m, 8H), 6.00 (m, 1H),
6.97 (m, 1H), 7.26 (m, 1H). 13C-NMR (CDCl3, 75
MHz, 25 °C): l=44.7, 65.9, 95.4, 129.4, 137.6, 169.2,
218.7 (CrꢁCO), 223.8 (CrꢁCO), 258.1 (CrꢀC). HRMS
(FAB); m/z: 356.9934 ([M+], calc. for C14H11CrNO7:
356.9941).
4.2. Synthesis of 2-pyranylidene–chromium complex 2
from 1 or 4a
4.2.5. 2-Pyranylidene–chromium complex 2e from 4a
The ketone 4a (0.13 g, 0.60 mmol) and Et3N (1.0 ml)
were used. A red solid (8% yield), m.p. 132.0–134.6 °C.
1
4.2.1. 2-Pyranylidene–chromium complex 2a from 1a
A solution of Cr(CO)6 (0.13 g, 0.60 mmol) in THF
(20 ml) and Et3N (0.1 ml) under Ar was irradiated by a
Hg lamp (350 nm) at room temperature (r.t.) for 4 h.
To this orange solution under Ar was added a solution
of 1a (33 mg, 0.20 mmol) in THF (1 ml) by a syringe.
The mixture was stirred at r.t. for 0.5–2 h. The solvent
was removed under reduced pressure, and the residue
IR (KBr, cm−1): 1918, 1974, 2051. H-NMR (THF-d8,
300 MHz, 25 °C): l=1.78–1.91 (m, 4H), 2.76–2.84
(m, 4H), 7.56–7.62 (m, 3H), 7.79–7.86 (m, 2H), 7.95 (s,
1H); 13C-NMR (THF-d8, 75 MHz, 25 °C): l=22.0,
23.0, 26.2, 29.6, 124.8, 129.6, 129.7, 132.0, 133.1, 141.0,
150.6, 175.5, 219.2 (CrꢁCO), 224.3 (CrꢁCO), 268.8
(CrꢀC). HRMS (FAB); m/z: 402.0185 ([M+], calc. for
C20H14CrO6: 402.0196).

232
K. Miki et al. / Journal of Organometallic Chemistry 645 (2002) 228–234
4.3. Typical procedure for [4+2] type cycloaddition of
2
l=21.5, 21.6, 22.2, 22.7, 125.3, 129.2, 130.3, 131.5,
132.8, 137.2, 163.3, 169.9, 218.2 (CrꢁCO), 232.3
(CrꢁCO), 276.4 (CrꢀC). HRMS (FAB); m/z: 407.9756
([M+], calc. for C19H12CrO6S: 407.9760).
4.3.1. Dimethyl 5,6,7,8-tetrahydro-1-methoxy-2,3-
naphthalenedicarboxylate (3a)
A mixture of complex 2a (0.034 g, 0.095 mmol) and
dimethyl acetylenedicarboxylate (0.2 ml, 1.6 mmol) in a
sealed tube was stirred at 90 °C for 12 h under N2. The
mixture was subjected to column chromatography on
SiO2 with hexane–EtOAc (v/v=10:1) as an eluent to
afford 3a (7 mg, 0.025 mmol, 26% yield) as a colorless
4.4.3. Tungsten complex 5c
A solution of W(CO)6 (0.21 g, 0.60 mmol) in THF
(20 ml) under Ar was irradiated by a Hg lamp (350 nm)
at r.t. for 4 h. To the yellow solution under Ar was
added a solution of 4a (42 mg, 0.2 mmol) in THF (1
ml) by a syringe. The mixture was stirred at r.t. for 0.5
h. The solvent was removed under reduced pressure,
and the residue was subjected to column chromatogra-
phy on SiO2 with hexane–EtOAc (v/v=10:1) as an
eluent to afford 5c (60 mg, 0.11 mmol, 56% yield) as a
blue solid. IR (KBr, cm−1): 580, 677, 825, 1920, 1934,
1
liquid. H-NMR (CDCl3, 300 MHz, 25 °C): l=1.77–
1.84 (m, 4H), 2.74–2.82 (m, 4H), 3.79 (s, 3H), 3.86 (s,
3H), 3.94 (s, 3H), 7.52 (s, 1H). 13C-NMR (CDCl3, 75
MHz, 25 °C): l=22.2, 22.4, 23.7, 29.3, 52.3, 52.6,
61.7, 125.3, 126.6, 127.2, 136.9, 140.4, 155.0, 165.8
(CO), 168.4 (CO).
1
2052. H-NMR (THF-d8, 300 MHz, 25 °C): l=1.94–
2.10 (m, 4H), 2.54–2.60 (m, 2H), 3.07–3.13 (m, 2H),
7.64–7.78 (m, 3H), 8.26–8.32 (m, 2H), 13.3 (s, 1H).
13C-NMR (THF-d8, 75 MHz, 25 °C): l=21.3, 22.5,
22.5, 23.5, 127.4, 127.9, 129.5, 129.8, 131.5, 141.7,
166.5, 171.3, 198.1 (WꢁCO), 210.2 (WꢁCO), 247.8
(WꢀC). HRMS (FAB); m/z: 534.0300 ([M+], calc. for
C20H14WO6: 534.0286).
4.3.2. Dimethyl 1-diethylamino-5,6,7,8-tetrahydro-2,3-
naphthalenedicarboxylate (3b)
A yellow liquid (25% yield). H-NMR (CDCl3, 300
MHz, 25 °C): l=1.00 (t, J=7.2 Hz, 6H), 1.72–1.82
(m, 4H), 2.65–2.75 (m, 2H), 2.75–2.86 (m, 2H), 2.90–
3.12 (m, 4H), 3.85 (s, 3H), 3.89 (s, 3H), 7.57 (s, 1H).
13C-NMR (CDCl3, 75 MHz, 25 °C): l=14.4, 22.4,
22.6, 26.6, 29.6, 47.4, 52.1, 52.2, 124.7, 128.1, 134.9,
139.4, 144.2, 146.8, 166.2 (CO), 169.8 (CO).
1
4.5. Synthesis of furfural deri6ati6es 6
4.5.1. Furfural 6a
4.4. Synthesis of furylcarbene complexes 5
A solution of 5a (22 mg, 0.054 mmol) in THF (5 ml)
was stirred at r.t. under O2 atmosphere for 12 h. The
solvent was removed under reduced pressure and the
residue was subjected to column chromatography on
SiO2 with hexane–EtOAc (v/v=8:1) as an eluent to
afford 6a (9.2 mg, 0.041 mmol, 76% yield) as a white
solid, m.p. 91.3–94.8 °C. IR (KBr, cm−1): 696, 773,
4.4.1. Chromium complex 5a
A solution of Cr(CO)6 (0.13 g, 0.60 mmol) in THF
(20 ml) under Ar was irradiated by a Hg lamp (350 nm)
at r.t. for 4 h. To the yellow solution under Ar was
added a solution of 4a (42 mg, 0.20 mmol) in THF (1
ml) by a syringe. The mixture was stirred at r.t. for 0.5
h. The solvent was removed under reduced pressure,
and the residue was subjected to column chromatogra-
phy on SiO2 with hexane–EtOAc (v/v=10:1) as an
eluent to afford 5a (42 mg, 0.10 mmol, 52% yield) as a
blue solid. IR (KBr, cm−1): 651, 826, 1934, 1994, 2045.
1H-NMR (THF-d8, 300 MHz, 25 °C): l=1.84–2.00
(m, 4H), 2.75–2.83 (m, 2H), 2.95–3.04 (m, 2H), 7.60–
7.69 (m, 3H), 8.16–8.25 (m, 2H), 13.5 (s, 1H). 13C-
NMR (THF-d8, 75 MHz, 25 °C): l=23.0, 24.0, 24.1,
24.4, 127.7, 128.8, 129.9, 130.8, 132.9, 138.4, 168.2,
171.7, 219.6 (CrꢁCO), 233.9 (CrꢁCO), 284.4 (CrꢀC).
HRMS (FAB); m/z: 402.0195 ([M+], calc. for
C20H14CrO6: 402.0219).
1
828, 1650, 1669. H-NMR (THF-d8, 300 MHz, 25 °C):
l=1.73–1.86 (m, 4H), 2.81–2.87 (m, 2H), 2.87–2.93
(m, 2H), 7.31–7.38 (m, 1H), 7.41–7.49 (m, 2H), 7.76–
7.81 (m, 2H), 9.73 (s, 1H). 13C-NMR (THF-d8, 75
MHz, 25 °C): l=22.8, 23.4, 23.9, 24.4, 122.6, 124.7,
127.1, 129.9, 130.2, 132.1, 147.8, 152.9, 178.2 (CHO).
HRMS (FAB); m/z: 227.1067 ([M+H+], calc. for
C15H14O2: 227.1072).
4.5.2. Furfural 6b
A white solid (76% yield), m.p. 100.5–101.6 °C. IR
(KBr, cm−1): 698, 819, 853, 1445, 1635, 1663. 1H-NMR
(THF-d8, 300 MHz, 25 °C): l=1.75–1.90 (m, 4H),
2.68–2.76 (m, 2H), 2.87–2.94 (m, 2H), 7.14 (dd, J=
3.6, 4.8 Hz, 1H), 7.42 (d, J=4.8 Hz, 1H), 7.47 (d,
J=3.6 Hz, 1H), 9.69 (s, 1H). 13C-NMR (THF-d8, 75
MHz, 25 °C): l=22.7, 23.1, 23.5, 24.1, 121.6, 126.6,
128.2, 129.3, 134.0, 136.7, 147.4, 149.6, 177.8 (CHO).
Anal. Calc. for C13H12O2S: C, 67.21; H, 5.21. Found:
C, 66.97; H, 5.17%.
4.4.2. Chromium complex 5b
A blue solid (59% yield). IR (KBr, cm−1): 1933,
1
1970, 2041. H-NMR (THF-d8, 300 MHz, 25 °C): l=
1.73–1.90 (m, 4H), 2.66 (t, J=3.9 Hz, 2H), 2.77 (t,
J=3.9 Hz, 2H), 7.27–7.31 (m, 1H), 7.88–7.94 (m, 2H),
13.0 (s, 1H). 13C-NMR (THF-d8, 75 MHz, 25 °C):

K. Miki et al. / Journal of Organometallic Chemistry 645 (2002) 228–234
233
ml) was added preformed phenylmagnesium bromide
(4.2 mmol) in THF (15 ml) at 0 °C, and the mixture
was stirred at r.t. for 4 h. The reaction mixture was
poured into saturated NH4Cl solution (30 ml), and the
aqueous layer was extracted with EtOAc (20 ml×3).
The combined organic layer was dried over MgSO4.
The solvent was removed under reduced pressure and
then 1 N KOH solution (2.0 ml) was added to the
residue in MeOH (20 ml) at r.t. After stirring for 0.5 h,
this solution was poured into saturated NH4Cl solution
(50 ml). The aqueous layer was extracted with EtOAc
(20 ml×3) and the combined organic layer was dried
over MgSO4. The solvent was removed under reduced
pressure and the residue was subjected to column chro-
matography on SiO2 with hexane–EtOAc (v/v=20:1)
as an eluent to afford 4a (0.22 g, 1.0 mmol, 52% yield)
as a colorless liquid. IR (neat, cm−1): 648, 690, 709,
732, 916, 1662 (C=O), 2093 (CꢂC), 3292 (ꢂCꢁH).
1H-NMR (CDCl3, 300 MHz, 25 °C): l=1.71–1.77 (m,
4H), 2.28–2.38 (m, 4H), 2.81 (s, 1H), 7.40–7.48 (m,
2H) 7.50–7.57 (m, 1H), 7.85–7.92 (m, 2H). 13C-NMR
(CDCl3, 75 MHz, 25 °C): l=21.4, 21.8, 27.3, 29.8,
82.2, 82.3, 119.8, 128.5, 129.5, 133.2, 136.0, 145.8, 199.0
(CO). HRMS (FAB); m/z: 211.1119 ([M+H+], calc.
for C15H14O: 211.1123).
Scheme 5.
4.6. Synthesis of substrates
Methyl 2-(trimethylsilyl)-1-cyclohexenecarboxylate
(10) was prepared from cyclohexanone in several steps:
see the supporting information of Ref. [6a] (Scheme 5).
4.6.1. N-Methyl N-methoxy
2-(trimethylsilyl)-1-cyclohexenecarboxamide (11) [13]
A solution of methyl 2-(trimethylsilylethynyl)-1-cy-
clohexenecarboxylate (10) (3.6 g, 15 mmol) in benzene
(5 ml) was added to benzene (40 ml) and hexane (45 ml)
solution of Me2AlNMe(OMe) prepared from a hexane
solution of Me3Al (45 ml, 45 mmol) and N,O-dimethyl-
hydroxylamine hydrochloride (4.4 g, 45 mmol). The
resulting solution was heated under reflux for 3 h. The
reaction mixture was cooled down to r.t., and hy-
drolyzed by slow and cautious addition of 1.0 N HCl
(30 ml). The upper organic layer was separated, and the
aqueous layer was extracted with EtOAc (30 ml×3).
The organic extracts were combined, washed with
brine, and dried over MgSO4. The solvent was removed
under reduced pressure to give the residual liquid,
which was subjected to column chromatography on
SiO2 with hexane–EtOAc (v/v=4:1) as an eluent to
afford N-methyl N-methoxy 2-(trimethylsilyl)-1-cyclo-
hexenecarboxamide (11) (3.6 g, 14 mmol, 92% yield) as
a pale yellow liquid. IR (KBr, cm−1): 845, 1659 (CꢀO),
4.7.2. 2-Ethynyl-1-cyclohexenyl 2-thienyl ketone (4b)
To a solution of thiophene (0.46 ml, 6.0 mmol) in
THF (5 ml) was added n-BuLi (4 ml, 1.6 M in hexane,
6.4 mmol) at 0 °C under N2, and the mixture was
stirred at r.t. for 2 h. This mixture was added to a
solution of 10 (0.80 g, 3.0 mmol) in THF (5 ml) at
0 °C, and the mixture was stirred at r.t. for 10 min. The
reaction mixture was poured into saturated NH4Cl
solution (20 ml), and the aqueous layer was extracted
with EtOAc (10 ml×3). The combined organic layer
was dried over MgSO4. The solvent was removed under
reduced pressure and then K2CO3 (1.0 g, 7.5 mmol) was
added to the residue in MeOH (30 ml) at r.t. After
stirring for 12 h, this solution was poured into satu-
rated NH4Cl solution (100 ml). The aqueous layer was
extracted with EtOAc (30 ml×3) and the combined
organic layer was dried over MgSO4. The solvent was
removed under reduced pressure and the residue was
subjected to column chromatography on SiO2 with
hexane–EtOAc (v/v=20:1) as an eluent to afford 4b
(0.28 g, 1.3 mmol, 43% yield) as a colorless liquid. IR
(neat, cm−1): 643, 734, 774, 856, 1262, 1285, 1411, 1644
(CꢀO), 2094 (CꢂC), 2935, 3288 (ꢂCꢁH). 1H-NMR
(CDCl3, 300 MHz, 25 °C): l=1.71–1.77 (m, 4H),
2.28–2.40 (m, 4H), 2.92 (s, 1H), 7.13 (dd, J=4.2, 4.2
Hz, 1H), 7.68 (d, J=4.2 Hz, 2H). 13C-NMR (CDCl3,
75 MHz, 25 °C): l=21.4, 21.7, 27.3, 29.7, 82.0, 82.2,
119.4, 128.1, 134.6, 134.7, 143.0, 145.8, 191.2 (CO).
HRMS (FAB); m/z: 217.0685 ([M+H+], calc. for
C13H12OS: 217.0687).
1
2144 (CꢂC). H-NMR (CDCl3, 300 MHz, 25 °C): l=
0.12 (s, 9H), 1.57–1.65 (m, 4H), 2.14–2.27 (m, 4H),
3.23 (s, 3H), 3.71 (s, 3H). 13C-NMR (CD2Cl2, 100
MHz, −25 °C): l= −0.1 (SiCH3), −0.1 (SiCH3),
21.5 (CH2), 21.5 (CH2), 21.8 (CH2), 21.9 (CH2), 26.5
(CH2), 26.7 (CH2), 28.8 (CH2), 29.5 (CH2), 31.8
(NCH3), 35.7 (NCH3), 60.3 (OCH3), 62.0 (OCH3), 96.4
(Cꢂ), 97.2 (Cꢂ), 103.0 (Cꢂ), 104.5 (Cꢂ), 116.7 (C=),
119.4 (C=), 140.0 (C=), 143.1 (C=), 166.4 (C=O),
170.8 (C=O) as a mixture of rotamers. Anal. Calc. for
C14H23NO2Si: C, 63.35; H, 8.73; N, 5.28. Found: C,
63.07; H, 8.47; N, 5.21%.
4.7. Preparation of i-ethynyl-h,i-unsaturated carbonyl
compounds 4
4.7.1. 2-Ethynyl-1-cyclohexenyl phenyl ketone (4a)
To a solution of 11 (0.47 g, 2.0 mmol) in THF (10

234
K. Miki et al. / Journal of Organometallic Chemistry 645 (2002) 228–234
[5] For reviews on vinylidene–metal complexes, see: (a) M.I. Bruce,
Acknowledgements
A.G. Swincer, Adv. Organomet. Chem. 22 (1983) 59;
(b) M.I. Bruce, Chem. Rev. 91 (1991) 197;
We thank Mr Yasuaki Hisamoto in our department
for measuring HRMS spectra. This research was sup-
ported on Priority Areas (A) ‘‘Exploitation of Multi-El-
ement Cyclic Molecules’’ from the Ministry of
Education, Culture, Sports, Science and Technology,
Japan.
(c) C. Bruneau, P.H. Dixneuf, Acc. Chem. Res. 32 (1999) 311.
[6] Preparation of pyranylidene–metal complexes via vinylidene–
metal intermediates, see: (a) K. Ohe, K. Miki, T. Yokoi, F.
Nishino, S. Uemura, Organometallics 19 (2000) 5525;
(b) N. Iwasawa, M. Shido, K. Maeyama, H. Kusama, J. Am.
Chem. Soc. 122 (2000) 10226.
[7] Transformation of vinylidene–metal intermediates in conjugated
systems, see: (a) Y. Wang, M.G. Finn, J. Am. Chem. Soc. 117
(1995) 8045;
(b) K. Ohe, M. Kojima, K. Yonehara, S. Uemura, Angew.
Chem. Int. Ed. Engl. 35 (1996) 1823;
References
(c) C.A. Merlic, M.E. Pauly, J. Am. Chem. Soc. 118 (1996)
11319;
(d) T. Manabe, S. Yanagi, K. Ohe, S. Uemura, Organometallics
17 (1998) 2942;
(e) K. Maeyama, N. Iwasawa, J. Am. Chem. Soc. 120 (1998)
1928;
(f) K. Maeyama, N. Iwasawa, J. Org. Chem. 64 (1999) 1344;
[1] L.S. Hegedus, Transition Metals in the Synthesis of Complex
Organic Molecules, University Science Books, Mill Valley, 1994,
p. 151.
[2] M.J. Winter, in: E.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.),
Comprehensive Organometallic Chemistry II, vol. 5, Pergamon/
Elsevier, Oxford, 1995, p. 155.
[3] For a review, see: F.E. McDonald, Chem. Eur. J. 5 (1999) 3103.
[4] For leading references, see: (a) E.O. Fischer, D. Plabst, Chem.
Ber. 107 (1974) 3326;
[8] (a) M. Wrighton, Chem. Rev. 74 (1974) 401;
(b) F.E. McDonald, C.C. Schultz, J. Am. Chem. Soc. 116 (1994)
9363.
[9] W. Strohmeier, K. Gerlach, Chem. Ber. 94 (1961) 398.
[10] A part of this work has been presented at the 79th Annual
Meeting of the Chemical Society of Japan in Kobe, March 31,
2001.
(b) C.P. Casey, R.L. Anderson, J. Chem. Soc. Chem. Commun.
(1975) 895;
(c) A. Parlier, H. Rudler, J. Chem. Soc. Chem. Commun. (1986)
514;
(d) K.H. Do¨tz, W. Sturm, H.G. Alt, Organometallics 6 (1987)
1424;
[11] Most recenty, Iwasawa and co-workers have reported the inter-
vention of a similar carbene complex in the tungsten-catalyzed
cyclization of 2-ethynylphenyl alkyl ketones. N. Iwasawa, M.
Shido, H. Kusama, J. Am. Chem. Soc. 123 (2001) 5814.
[12] Chromium moieties are readily displaced with the oxygen atom
by molecular oxygen, see: (a) R.B. Silveman, R.A. Olofson,
Chem. Commun. (1968) 1313;
(b) E.O. Fischer, S. Riedmu¨ller, Chem. Ber. 107 (1974) 915.
[13] For preparation of ketones, see: (a) M.F. Lipton, A. Baska, S.M.
Weinreb, Org. Synth. 59 (1979) 49;
(e) F.E. McDonald, C.B. Connolly, M.M. Gleason, T.B. Towne,
K.D. Treiber, J. Org. Chem. 58 (1993) 6952;
(f) P. Quayle, S. Rahman, E.L.M. Ward, J. Herbert, Tetrahe-
dron Lett. 35 (1994) 3801;
(g) F.E. McDonald, M.M. Gleason, J. Am. Chem. Soc. 118
(1996) 6648;
(h) B. Schmidt, P. Kocienski, G. Reid, Tetrahedron 52 (1996)
1617;
(i) C.F. Bernasconi, Chem. Soc. Rev. 26 (1997) 299;
(j) F.E. McDonald, H.Y.H. Zhu, J. Am. Chem. Soc. 120 (1998)
4246;
(b) J.I. Levin, E. Turos, S.M. Weinreb, Synth. Commun. 12
(1982) 989;
(c) S. Nahm, S.M. Weinreb, Tetrahedron Lett. 22 (1981) 3815.
(k) F.E. McDonald, K.S. Reddy, Y. D´ıaz, J. Am. Chem. Soc.
122 (2000) 4304;