Synthesis of 3-silyl-2(5H)-furanone by rhodium-catalyzed cyclocarbonylation

Article abstract of DOI:10.1016/S0040-4039(00)02234-6

3-Silyl-2(5H)-furanones are readily formed by the rhodium-catalyzed cyclocarbonylation of propargyl alcohol derivatives bearing a trialkylsilyl group on the terminal sp-carbon under hydroformylation conditions. The following two requirements must be satisfied for the success of this protocol; (i) the presence of a silyl group on the sp-carbon, and (ii) the presence of a catalytic amount of Rh₄(CO)₁₂.

Full text of DOI:10.1016/S0040-4039(00)02234-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 1301–1304
Synthesis of 3-silyl-2(5H)-furanone by rhodium-catalyzed
cyclocarbonylation
Yukimasa Fukuta, Isamu Matsuda* and Kenji Itoh
Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa,
Nagoya 464-8603, Japan
Received 5 December 2000; accepted 6 December 2000
Abstract—3-Silyl-2(5H)-furanones are readily formed by the rhodium-catalyzed cyclocarbonylation of propargyl alcohol deriva-
tives bearing a trialkylsilyl group on the terminal sp-carbon under hydroformylation conditions. The following two requirements
must be satisfied for the success of this protocol; (i) the presence of a silyl group on the sp-carbon, and (ii) the presence of a
catalytic amount of Rh4(CO)12. © 2001 Elsevier Science Ltd. All rights reserved.
Regio-control for the incorporation of CO into a start-
ing substrate has been an outstanding issue since the
discovery of the Roelen reaction (oxo reaction). Hydro-
formylation of alkene has been widely investigated, and
there are many excellent papers concerning the regio-
chemistry of terminal alkenes.1 However, little is known
about the regio-control in hydroformylation of alkynes
to give an unsaturated aldehyde because hydrogenation
of the primary product proceeds under the reaction
conditions.2–4 During our project on the Rh-catalyzed
selective incorporation of CO into alkynes, we explored
rhodium-catalyzed silylformylation of alkynes, in which
complete regio-control was realized by using a hydrosi-
lane.5
a trialkylsilyl group on the sp-carbon smoothly incor-
porate CO to form a 2(5H)-furanone framework. We
describe here a one-pot procedure for the synthesis of
3-silyl-2(5H)-furanones composed of 1-substituted-3-
silylpropyn-1-ols, CO, and H2 in the presence of a
catalytic amount of Rh4(CO)12.
First of all, a benzene solution of 1-(trimethylsilyl-
ethynyl)cyclohexan-1-ol (1a, R=SiMe3, 1.0 mmol) and
a catalytic amount of Rh4(CO)12 (0.25 mol% of 1a) was
heated for 3 h at 90°C under synthesis gas pressure (40
kg/cm2, CO/H2=1/1) in a glass tube contained in a
stainless steel reactor. Chromatographic separation of
the reaction mixture through silica gel gave two prod-
ucts, a spiro butenolide (2a)6 and 2-cyclohexylidene-3-
trimethylsilylpropanal (3a)6 in 92 and 3% yields,
respectively (Eq. (1)).
As the primary target at the second stage of this
project, we concentrated on the regio-control in the
R
CO / H2 (40 kg/cm2)
R
R
CHO
(1)
+
Rh4(CO)12 (0.25 mol%)
OH
O
O
C6H6, 90 ˚C, 3 h
2
1
3
reaction of alkynes under hydroformylation conditions.
Thus, we focussed on rhodium-catalyzed reaction of
propargyl-type alcohols and found that alkynes bearing
This result shows clearly that the selective incorpora-
tion of CO is attained on the silylated sp-carbon of 1a.
It should be noted that the resultant carbonꢀcarbon
double bond remained intact in both products 2a and
3a, although the reaction of 1a was operated under the
equal pressure of H2 with CO. We are stimulated by
this preliminary evidence because the present reaction
provides a protocol for the incorporation of CO into
Keywords: cyclocarbonylation; rhodium complex; synthesis gas;
2(5H)-furanone.
* Corresponding author. Fax: +81-52-789-3205; e-mail: matsudai@
apchem.nagoya-u.ac.jp
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)02234-6

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Y. Fukuta et al. / Tetrahedron Letters 42 (2001) 1301–1304
the terminal sp-carbon of 1b. Selective incorporation of
CO into the terminal sp-carbon of 1b has been attained
as shown in Eq. (2).5b
exclusively although high pressure of the synthesis gas
was required for the complete conversion of 1a (entry 10
in Table 1). Other solvents, CH2Cl2, CH3CN, and
SitBuMe2
tBuMe2SiH
CO (20 kg/cm2)
O
(2)
O
Rh4(CO)12, DBU (cat.)
C6H6, 90 ˚C, 2 h
OH
1b
4
Thus, some variable factors were examined for exploring
the optimal conditions. The results are summarized in
Table 1. The overall carbonylation proceeded uniformly
in a benzene solution under the pressure of synthesis gas
from 2 to 40 kg/cm2. The isolated yield of 2a increased
to 97% under 20 kg/cm2 of synthesis gas (entry 2 in Table
1), while no products were obtained in the reaction under
the atmosphere of CO/H2 (entry 4 in Table 1). In sharp
contrast to the result of Eq. (2), the incorporation of CO
was completely suppressed by the presence of a catalytic
amount of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene)
(entry 5 in Table 1). To the contrary, 2a was isolated in
79% yield as the sole product despite the incomplete
conversion of 1a in the presence of 1,2,2,6,6-pentamethyl-
piperidine (4 mol%) (entry 6 in Table 1). Other rhodium
EtOH, resulted in low yields of 2a (entries 11–13 in Table
1). Yamazaki and co-workers reported the incorporation
of two molecules of CO into an alkyne to give an
alkoxyfuranone in the reaction using methanol as a
solvent.7 In our case, however, the corresponding
product was not detected at all even in the reaction using
ethanol as a solvent.
The presence of a silyl group on the sp-carbon seems to
be crucial for smooth incorporation of CO in the
present-type cyclocarbonylation. Alkynols bearing tert-
BuMe2Si (1c), Et3Si (1d), and Me2PhSi (1e) as R reacted
uniformly to give 26 (entries 14–16 in Table 1), while
other alkynols (R=H, phenyl, n-butyl, and methoxycar-
bonyl) resulted in no reaction with recovery of the
starting materials under similar conditions. In contrast
to Rh-catalyst, a similar transformation catalyzed by
Pd2(dba)3·CHCl3 is free from this constraint.8 Our
method, however, makes it possible to shorten apprecia-
bly the time required for completion in the reaction of
specific substrates.
complexes, Rh(CO)2(acac), [Rh(cod)(dppb)]+ClO4 , and
−
[RhCl(CO)2]2 did not exceed the efficiency of Rh4(CO)12
as a catalyst precursor (entries 7–9 in Table 1).
The nature of solvents affected the efficacy for the
incorporation of CO. When THF was employed as a
solvent instead of benzene, 2a was obtained almost
Table 1. Cyclocarbonylation of 1a
Entry
Alkyne (1)
Pressure of CO/H2 (kg/cm2)
Solvent
Time (h)
Yield (%)b
Recovery (%)
R
2
3
1
1
2
3
4
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1c
1d
1e
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
40
20
2
C6H6
C6H6
C6H6
C6H6
C6H6
C6H6
C6H6
C6H6
C6H6
THF
CH2Cl2
CH3CN
EtOH
C6H6
C6H6
C6H6
3
3
13
6
3
3
3
3
3
3
3
3
3
3
3
3
92
97
89
0
3
<1
3
0
0
0
0
0
0
<1
0
0
0
6
0
0
8
1
>90
>90
11
62
85
>90
0
61
74
40
0
5c
6d
7e
8f
20
20
20
20
20
40
20
20
20
20
20
40
0
79
37
15
0
99
27
14
46
92
77
79
9g
10
11
12
13
14
15
16
tBuMe2Si
Et3Si
Me2PhSi
3
0
0
0
a Reactions were carried out on a 1.0 mmol scale of 1 at 90°C using Rh4(CO)12 (0.25 mol%) as a catalyst under synthesis gas pressure
(CO/H2=1/1).
b Isolated yields.
c 5 mol% of DBU was added.
d 4 mol% of 1,2,2,6,6-pentamethylpiperidine was added.
e Rh(CO)2(acac) (1.0 mol%) was used as a catalyst.
−
f [Rh(cod)(dppb)]+ClO4 (1.0 mol%) was used as a catalyst.
g [RhCl(CO)2]2 (0.5 mol%) was used as a catalyst.

Y. Fukuta et al. / Tetrahedron Letters 42 (2001) 1301–1304
Table 2. Rhodium-catalyzed cyclocarbonylation of 5a
1303
Entry
Alkynol (5)
R2
Solvent
CO/H2 (kg/cm2)
Yield (%)b
Ratio
R1
66
6:7c
1
2
3
4
5
6
7
8
5a
5b
5c
5d
5e
5f
-(CH2)4-
-(CH2)6-
THF
THF
C6H6
C6H6
C6H6
C6H6
THF
C6H6
THF
C6H6
THF
C6H6
40d
40
20
20
20
40
40
40
40
40
40
40
6a
6b
6c
6d
6e
6f
82
95
83
88
85
67
72
74
76
76e
95e
0f
95:5
99:1
98:2
97:3
94:6
90:10
96:4
93:7
93:7
88:12
96:4
–
Et
Me
Ph
H
H
H
H
H
H
H
Et
Ph
Ph
Oct
5f
Oct
6f
5g
5g
5h
5h
5i
iPr
6g
6g
6h
6h
6i
9
iPr
10
11
12
Ph
Ph
CHꢁCHPh
a Reactions were carried out on a 1.0 mmol scale of 5 containing a Rh4(CO)12 (0.25 mol%) for 3 h at 90°C under synthesis gas pressure
(CO/H2=1/1).
b Isolated yields.
c The ratio was estimated from NMR spectrum of a crude mixture.
d The reaction was carried out for 12 h.
e The yield was estimated from NMR spectrum after a bulb-to-bulb distillation of a crude mixture.
f 5i was recovered intact.
SiMe3
O
SiMe3
R2
R1
SiMe3
CHO
CO/H2
R2
R1
+
R2
R1
Rh4(CO)12
(3)
O
OH
5
6
7
Next, various types of propargyl alcohol (5) were sub-
jected to the present carbonylation in order to clarify
the scope and limitation of the method. The results are
summarized in Table 2. Alkynols bearing two sub-
stituents on the propargyl position (5a–e) gave the
corresponding furanones6 in high yields and high regio-
selectivity (entries 1–5 in Table 2). Less substituted ones
resulted in a slight decrease of the selectivity for 6
(entries 6, 8, and 10 in Table 2) in addition to the
requirement of relatively high pressure of synthesis gas
(40 kg/cm2) for the complete conversion of 5. The yield
and the selectivity of 6f–h6 were remarkably improved
The position of the hydroxy group in the starting
substrates also affected the reaction path. Two types of
lactone were isolated as major products in the carbony-
lation of silylated alkynes 8 and 11, respectively, under
analogous conditions (Eqs. (4) and (5)). These results
imply that the rhodium species cannot kinetically differ-
entiate two sp-carbons of alkynes, 8 and 11, under the
conditions. Therefore, intervention of a thermodynami-
cally controlled step should be assumed for elucidation
of the remarkable high regio-selectivity in the reactions
of 1 and 5.
(4)
(5)
Our protocol was also applied to a steroidal propargyl
alcohol 14 to form a spiro lactone 15 as the sole
product (93%) (Eq. (6)). In this reaction, the olefinic
unit of 14 remained intact after the carbonylation step.
A similar transformation has been attained through
hydroformylation of an alkynol part in which an oxida-
tion step was inevitably required for the dehydrogena-
tion from the lactol intermediate.10
by replacing benzene with THF as the solvent. In
particular, the yield of 6h increased to 95% (entries 7, 9,
and 11 in Table 2). In sharp contrast to these results, a
styryl group on the propargyl carbon inhibited car-
bonylation under our conditions (entry 12 in Table 2),
although the incorporation of CO was reported in the
reaction of 1,4-diphenylbut-1-en-3-yne.9

1304
Y. Fukuta et al. / Tetrahedron Letters 42 (2001) 1301–1304
(6)
In summary, we have developed a new method for the
transformation of propargyl alcohols to form 2(5H)-
furanones bearing a trialkylsilyl group, in which Rh4-
(CO)12 is the most suitable as a catalyst under hydro-
formylation conditions. We have described the scope
and limitation of this protocol and demonstrated the
successful result for ethisterone. The trialkylsilyl group
contained in the resultant furanones would become an
important clue for various transformations.11
4. (a) Van den Hoven, B. G.; Alper, H. J. Org. Chem. 1999,
64, 3964; (b) Van den Hoven, B. G.; Alper, H. J. Org.
Chem. 1999, 64, 9640.
5. (a) Matsuda, I.; Ogiso, A.; Sato, S.; Izumi, Y. J. Am. Soc.
Chem. 1989, 111, 2332; (b) Matsuda, I.; Ogiso, A.; Sato,
S. J. Am. Chem. Soc. 1990, 112, 6120; (c) Matsuda, I.;
Sakakibara, J.; Nagashima, H. Tetrahedron Lett. 1991,
32, 7431; (d) Monteil, F.; Matsuda, I.; Alper, H. J. Am.
Chem. Soc. 1995, 117, 4419; (e) Ojima, I.; Vidal, E.;
Tzamarioudaki, M.; Matsuda, I. J. Am. Chem. Soc. 1995,
117, 6797; (f) Matsuda, I.; Fukuta, Y.; Tsuchihashi, T.;
Nagashima, H.; Itoh, K. Organometallics 1997, 16, 4327.
6. All these compounds were identified by 1H NMR, 13C
NMR and IR spectra. All new compounds gave satisfac-
tory combustion analyses. For example, 2a: white needles
from hexane (mp 117.2–117.5°C). IR (CCl4): 1751 (wCꢁO),
Acknowledgements
We
gratefully
acknowledge
financial
support
(12450360) from the Ministry of Education, Science,
Sports, and Culture, Japanese Government.
1597 (wCꢁC), 1252 (wSiꢀC) cm−1 1H NMR (CDCl3, 300
.
MHz) l: 0.23 (s, 9H, Si-(CH3)3), 1.25–1.79 (m, 10H,
-(CH2)5-), 7.45 (s, 1H, ꢁCH). 13C NMR (CDCl3, 75
MHz) l: −2.08 (SiCH3), 22.50 (-(CH2)5-), 24.63 (-(CH2)5-),
34.55 (-(CH2)5-), 88.21 (OC), 132.60 (ꢁCSi), 168.12
(ꢁCH), 174.77 (CꢁO). Anal. calcd for C12H20O2Si: C,
64.24; H, 8.98. Found: C, 64.30; H, 9.11.
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