Glycerol - A non-innocent solvent for Rh-catalysed Pauson-Khand carbocyclisations

Article abstract of DOI:10.1002/ejic.201300651

Rh-catalysed carbocyclisations of the 1,6-enynes 1-8 efficiently gave bicyclo[3.3.0]octenones in neat glycerol. Unexpectedly, ligand-free [Rh(μ-OMe)(cod)]₂ was highly selective. Moreover, TPPTS [tris(3-sulfonatophenyl)phosphane trisodium salt]

Full text of DOI:10.1002/ejic.201300651

FULL PAPER
DOI:10.1002/ejic.201300651
Glycerol – A Non-Innocent Solvent for Rh-Catalysed
Pauson–Khand Carbocyclisations
[
a]
[a,b]
Kevin Fourmy,[b]
Faouzi Chahdoura, Laurent Dubrulle,
[
b]
[a]
[a]
Jérôme Durand,* David Madec, and Montserrat Gómez*
Keywords: C–C coupling / Rhodium / Reaction mechanisms / NMR spectroscopy / Glycerol
Rh-catalysed carbocyclisations of the 1,6-enynes 1–8 ef-
ficiently gave bicyclo[3.3.0]octenones in neat glycerol. Unex-
pectedly, ligand-free [Rh(μ-OMe)(cod)] was highly selective.
2
Moreover, TPPTS [tris(3-sulfonatophenyl)phosphane triso-
dium salt] improved the catalyst performance at low Rh/L
ratios, but surprisingly, ligand excess blocked the reaction.
Detailed NMR studies evidenced the role of glycerol in the
catalytic process.
Introduction
which is synthesized from biomass and is currently pro-
duced in high amounts as waste in the biodiesel production.
Its low cost, non-toxicity, high boiling point, negligible vap-
our pressure, high solubility for organic and inorganic com-
pounds, and low miscibility with other organic solvents,
constitute attractive properties for applications in catalysis.
However, the potential reactivity of its hydroxy groups can
lead to by-products, mainly, when one is working under
strong basic conditions. However, these groups can also
participate in acid–base exchanges, inducing positive effects
in the elementary catalytic steps.
The synthesis of highly functionalised organic molecules
often results in large amounts of waste products because of
the multitude of reagents and the number of purification
steps involved, which leads to a strong negative environ-
mental impact and expensive processes. Thus, the develop-
ment of multi-step syntheses, in which several bonds are
formed in “one-pot” reactions, is a good tool to reduce this
effect. This solution becomes particularly attractive when
one is working under catalytic conditions, in which case it
amplifies the atom economy[1] and decreases the required
energy, which is in accordance with the green chemistry
To the best of our knowledge, the use of glycerol in the
PKR represents a pioneering work in the literature. Herein,
we report the influence of this medium using the complexes
[
2]
principles. In the last ten years, alternatives to commonly
used organic, volatile solvents have been studied: ionic li-
quids, water, supercritical fluids, and perfluorinated sol-
–
–
[
Rh(μ-X)(cod)] (X = OMe , Cl ) as catalytic precursors.
2
The effect of mono- and diphosphane ligands was also
evaluated. A NMR study was carried out to understand
the different species that formed depending on the catalytic
system.
[
3]
vents. However, the general use of such alternatives still
has some limitations, such as high cost, a lack of data con-
cerning toxicity and biodegradability, and the separation of
products. The Rh-catalysed [2+2+1] Pauson–Khand car-
bocyclisation reaction (PKR)[ appeared to us as an excel-
lent example to illustrate the complementarity of these two
4]
concepts. The PKR comprises the simultaneous formation Results and Discussion
of three C–C bonds and the insertion of a carbonyl func-
tionality from carbon monoxide. We chose to develop the
We chose the 1,6-enynes 1–3 as model substrates for our
PKR in neat glycerol,[ an innovative solvent in catalysis, preliminary tests concerning the Rh-catalysed PKR in glyc-
5]
erol (Scheme 1).
The use of [Rh(μ-OMe)(cod)] as a catalytic precursor
[
a] Laboratoire Hétérochimie Fondamentale et Appliquée UMR
CNRS 5069 Université Paul Sabatier,
2
afforded active catalytic systems in glycerol, and using the
substrates 1–3 in the absence of an additional ligand and a
silver salt led to 90% (1a and 3a) and 60% (for 2a) isolated
1
18, route de Narbonne, 31062 Toulouse Cedex 9, France
E-mail: gomez@chimie.ups-tlse.fr
http://hfa.ups-tlse.fr/
[
b] Laboratoire de Chimie de Coordination UPR CNRS 8241 - yields (Table 1, entries 1–3). At a shorter reaction time, the
Composante ENSIACET,
bicyclo[3.3.0]octenone 1a was obtained in high yield (82%,
Table 1, entry 4). Surprisingly, under similar conditions, the
4
, Allée Emile Monso, BP 44362, 31030 Toulouse Cedex 4,
France
E-mail: Jerome.durand@ensiacet.fr
[
Rh(μ-Cl)(cod)] precursor was practically inactive for these
2
Homepage: http://www.lcc-toulouse.fr/
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300651.
substrates (conversions Ͻ5%). The beneficial influence of
glycerol was evidenced by comparison with different or-
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Whereas the catalytic system using [Rh(μ-OMe)(cod)]2/
TPPTS in a 1:1 Rh/ligand ratio was very active and selective
(up to 90% isolated yield for 1a, entry 9 in Table 1), the 1:2
Rh/ligand ratio led to an inactive system (Table 1, entry 10).
Consistent with these results, when the bidentate ligand rac-
BINAP (Scheme 1) was used, the corresponding Rh–BI-
NAP system was also inactive (Table 1, entry 11). In an
attempt to increase the catalytic activity, [Rh(μ-Cl)(cod)]2
was treated with silver triflate, but no reaction was detected
even after 24 h (Table 1, entry 12). This behaviour strongly
contrasts with the data reported for studies with thf as the
[
11]
solvent.
Other related substrates were tested under the best condi-
tions found for substrate 1, and this proved the high effi-
ciency of the catalytic system (Table 2). The presence of
electron-donor groups on the aryl fragment triggers an ac-
tivity increase (Table 2, entries 1 and 2 vs. 3 and 4), which
Scheme 1. Rh-catalysed PKR of enynes 1–3 (L = TPPTS, rac-BI-
NAP).
ganic solvents. Whereas in toluene, a non-coordinating sol- is in agreement with the trend observed for organic sol-
[
10c]
vent, [Rh(μ-OMe)(cod)] exhibited a low activity (less than vents.
Surprisingly, despite a potential Thorpe–Ingold
2
1
0% conversion for substrates 1 and 2; Table 1, entries 5 effect, the enyne 8 afforded the corresponding bicyclo-
and 6), full conversion of 1 was achieved when the coordi- [3.3.0]octenone in a slightly lower yield (Table 2, entry 2 vs.
nating solvent thf was used. However, in this case, the reac- 5).
tion suffers from a low chemoselectivity (40% yield,
These results evidence a non-innocent role of glycerol in
Table 1, entry 7). A decrease in the CO pressure for the the PKR. We were especially interested in understanding
PKR of 1 in glycerol induced a higher catalytic activity the catalytic influence of the anion bridge of the organome-
(
Table 1, entry 8 vs. 4), which is in agreement with similar tallic precursor and of the ligand. Some NMR experiments
observations related to the PKR in conventional organic were thus carried out to better understand this behaviour.
[
6]
solvents. In total absence of CO, the system is inactive,
The catalytic activity associated to [Rh(μ-OMe)(cod)] is
2
evidencing that under these reaction conditions glycerol in contrast to the lack of activity observed with [Rh(μ-
cannot act as a CO source, which is in contrast to results Cl)(cod)] . This can be associated to the Brønsted-basic
2
[7]
described in the works of Chung et al. and Morimoto et character of the methoxide group in a protic medium such
al.,[ in which alcohols or aldoses were used as CO sources, as glycerol.
8]
[12]
To evidence the plausible proton exchange,
H and C NMR spectra for both organometallic precur-
1
13
respectively.
Aldehydes have also been reported as alternative CO sors were analysed in CD Cl {[Rh(μ-X)(cod)] /glycerol =
2
2
2
sources for Rh-catalysed PKR.[ The addition of cinnam- 1:2, X = Cl , OMe } (Figs. S1–S4). The C NMR spectrum
9]
–
–
13
aldehyde to our catalytic mixture did not lead to its Rh- of [Rh(μ-OMe)(cod)] (Figure 1, b) shows the presence of
2
catalysed decarbonylation, which is in contrast to previous two rhodium species, which can be clearly identified by the
[
10]
reports.
signals corresponding to the coordinated cyclooctadiene
To study the influence of phosphanes on the PKR reac- [two doublets in the methylene region: 78.7 ppm,
tion in glycerol, we chose TPPTS (Scheme 1) because of its JRh–(CH=CH) = 14 Hz; 74.1 ppm, JRh–(CH=CH) = 14.8 Hz;
higher solubility in this medium compared to PPh3.
two singlets in the aliphatic region: 30.9 and 30.6 ppm], be-
I
[a]
Table 1. Rh -catalysed Pauson–Khand reaction using 1, 2 and 3 as 1,6-enynes.
Entry Enyne
Ligand (Rh/P)
Solvent
pCO [bar]
Reaction time [h] Temperature [°C] Conversion[b] (isolated yield) [%]
1
2
3
4
5
6
7
8
9
1
1
1
1
2
3
1
1
2
1
1
1
1
1
1
–
–
–
–
–
–
–
–
glycerol
glycerol
glycerol
glycerol
toluene
toluene
thf
glycerol
glycerol
glycerol
1
1
1
1
1
1
1
0.5
1
1
16
16
16
4
16
16
16
4
80
80
80
100 (90)
100 (60)
100 (90)
82 (82)
10
80
reflux
reflux
reflux
80
80
80
5
100 (40)
90 (90)
90 (90)
0
TPPTS (1:1)
TPPTS (1:2)
4
0
1
2
24
24
24
rac-BINAP (1:1) glycerol
1
1
80
80
0
0
rac-BINAP (1:1)[ glycerol
c]
[
a] Reaction conditions: [Rh(μ-OMe)(cod)]
2
as catalytic precursor; Rh/enyne = 1:20; 5 mL of solvent. [b] Determined by 1H NMR
spectroscopy. [c] [Rh(μ-Cl)(cod)] /BINAP/AgOTf = 0.5:1:1.
2
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I
[a]
Table 2. Rh -catalysed Pauson–Khand reactions using 4–8 as 1,6-enynes.
[
2
a] Reaction conditions: [Rh(μ-OMe)(cod)] as catalytic precursor; Rh/enyne = 1:20; 5 mL of glycerol; 80 °C; 0.5 bar CO; 4 h. [b] Deter-
1
mined by H NMR spectroscopy.
Figure 1. Comparison between 13C NMR spectra (76.5 MHz, CD
glycerol. Rh/glycerol = 1:1.
2
2 2 2
Cl , 298 K) of [Rh(μ-Cl)(cod)] (a) and [Rh(μ-OMe)(cod)] (b) in
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sides the appearance of a CH OH resonance. This is in con- as signals of free COD and sharp signals for CH OH and
3
3
trast to the unique species observed for [Rh(μ-Cl)(cod)] [δ glycerol (Figure S5), all of which suggests an irreversible
2
=
78.6 ppm (d), J
= 14.9 Hz; 30.9 ppm (s), Fig- process [Equation (2), Scheme 2]. The two sets of signals
Rh–(CH=CH)
[
13]
ure 1, a].
These facts agree with the coexistence of two can be attributed to dimeric Rh species containing one and
Rh dimers, in one of which deprotonated glycerol acts as a two equivalents of diphosphane per Rh starting complex
bridging ligand [Equation (1), Scheme 2].
(compounds A and B, Scheme 2); the two observed dif-
ferently coordinated COD ligands can be due to the dif-
ferent nature of the bridging alkoxide group. Subsequent
CO addition leads to the formation of two main species
[
16]
(
Figure 2, bottom). One of them has non-equivalent P
atoms [δ = 45.6 ppm (dd), JRh–P = 161.6 Hz, JP–P
3.7 Hz; 23.7 ppm (dd), JRh–P = 127.6 Hz, JP–P = 43.7 Hz],
which is consistent with monometallic Rh complexes coor-
=
4
[
15]
dinated to CO and BINAP (C, Scheme 2); the other one
exhibits a symmetrical environment, which leads to a
unique doublet corresponding to a neutral species (δ =
4
6.9 ppm, J
= 172 Hz) (D, Scheme 2). In the CO re-
Rh–P
13
gion, the C NMR spectrum exhibits a doublet of doublets
of doublets (δ =186.9 ppm, JRh–CO = 79.2 Hz, JPtrans–CO
7.8 Hz, JPcis–CO = 2.5 Hz), which is in agreement with one
=
1
CO ligand coordinated to the metal complex containing
BINAP (Figure S6). Further addition of enynes (1 or 2) did
not lead to the corresponding bicyclo[3.3.0]octenones (1a
or 2a), which shows that these saturated rhodium species
are not able to coordinate the 1,6-enyne, which prevents the
carbocyclisation because of the lack of enough labile posi-
I
Scheme 2. Rh species generated from [Rh(μ-OMe)(cod)]
2
in glyc-
erol in the presence of rac-BINAP.
tions around the metal centre. For [Rh(μ-Cl)(cod)]
same pattern of signals is observed after addition of rac-
Further addition of rac-BINAP (Scheme 1) to the [Rh(μ- BINAP and CO (Figure S7).
2
, the
OMe)(cod)] glycerol solution leads to the formation of two
However, Rh–TPPTS catalytic systems with monophos-
2
main rhodium species, as evidenced by the two close dou- phane/Rh ratios lower than 2 lead to active species, as ob-
3
1
blets observed by P NMR spectroscopy (δ = 49.3 ppm, served with TPPTS (Table 1, entry 9). For low TPPTS con-
JRh–P = 207 Hz; 48.9 ppm, JRh–P = 199 Hz) (Figure 2, top). tent, unsaturated Rh species stabilised by coordinated glyc-
In agreement with the literature,[
14,15]
their Rh–P cou- erol can be envisaged, which could be responsible for the
pling constants and chemical shifts point to the formation catalytic activity, as proposed in Scheme S1.
1
of neutral species, where the diphosphane does not act as a
The H NMR monitoring of [Rh(μ-OMe)(cod)] in the
2
1
3
bridging ligand. The C NMR spectrum exhibits signals of presence of CO evidences the formation of both free COD
two differently coordinated cyclooctadiene ligands, as well and CH OH, which allows for the formation of cationic Rh
3
Figure 2. 31P NMR spectra (121.5 MHz, CD
subsequent addition of 1 bar CO (bottom). Rh/L/glycerol = 1:1:1. The signal at approximately 40 ppm is attributed to phosphane oxide.
2
2 2
Cl , 298 K) of [Rh(μ-OMe)(cod)] in glycerol after addition of rac-BINAP (top) and after
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species I (Scheme 3 and Figure S8), which favours a biden- Experimental Section
tate enyne coordination (species II in Scheme 3). The for-
mation of bicyclo[3.3.0]octenone 2a could be observed after
General: NMR spectra were recorded with a Bruker Avance 300
1
13
(
300 MHz for H NMR, 76.5 MHz for C NMR, and 121.5 MHz
addition of 2. When [Rh(μ-Cl)(cod)] was used under the
31
2
for P NMR spectra).
same conditions, no COD decoordination was observed
The 1,6-enynes N-allyl-N-(3-phenyl-2-propynyl)-4-tolylsulfonamide
(Figure S8); the subsequent addition of enyne did not afford
18]
[19]
(
1),[
3-allyloxy-1-phenylpropyne (2),
3-allyloxy-1-(4Ј-meth-
and N-allyl-N-[3-(4Ј-methoxyphenyl)-2-
propynyl]-4-tolylsulfonamide (4), and N-allyl-N-[3-(4Ј-nitro-
the Pauson–Khand product. Inactive species such as
[20]
oxyphenyl)propyne (5),
[
RhCl(cod)(CO)] could probably be formed.
[21]
phenyl)-2-propynyl]-4-tolylsulfonamide (6) were prepared as de-
scribed in the literature. Diethyl allyl(3-phenyl-2-propynyl)malon-
ate (3) was purchased from Alfa Aesar and used without further
purification. Glycerol (99%, purchased from Sigma–Aldrich) was
treated under vacuum at 80 °C overnight prior to use. The organic
solvents were purified by standard procedures and distilled under
nitrogen. [Rh(μ-Cl)(cod)]
2
was commercially available, and [Rh(μ-
[
22]
OMe)(cod)] was prepared by following a reported methodology.
2
Synthesis of Enyne 7
1
3
-Iodo-4-nitrobenzene (1.24 g, 5 mmol), [PdCl
2 3 2
(PPh ) ] (0.10 g,
mol-%), CuI (0.057 g, 6 mol-%), Et N (1.4 mL, 10 mmol), pro-
3
pargyl alcohol (0.302 mL, 5.2 mmol), and freshly distilled thf
5 mL) were introduced into a round-bottom flask with a Teflon
(
inter-key under argon. The resulting dark-brown reaction mixture
was stirred at 30–35 °C for 3 h (up to complete consumption of the
iodo derivative, which was monitored by GC analysis). The product
corresponding to the Sonogashira coupling was obtained as a light-
brown solid after the evaporation of thf, and it was purified by
flash column chromatography on silica gel by using dichlorometh-
1
ane as the eluent (0.8 g, 90% yield). H NMR (CDCl
3
, 300 MHz):
I
Scheme 3. Rh species proposed for the PKR catalysed by [Rh(μ-
δ = 8.18 (d, J = 8.0 Hz, 2 H), 7.56 (d, J = 8.0 Hz, 2 H), 4.54 (s, 2
OMe)(cod)]
2
in glycerol under ligand-free conditions consistent
with NMR studies (S = glycerol).
13
H), 2.08 (br. s, 1 H) ppm. C NMR (CDCl
3
, 76.4 MHz): δ = 147.4,
132.3, 129.6, 123.2, 92.6, 83.7, 51.4 ppm. MS (EI): m/z = 177.04.
3-(4-Nitrophenyl)-2-propyn-1-ol (0.7 g, 4 mmol), NaH (144 mg,
As stated above, the PKR also takes place in thf as coor- 6 mmol), allyl bromide (0.17 mL, 6 mmol), and freshly distilled thf
dinating solvent but with low selectivity (Table 1, entry 7), (10 mL) were mixed at room temperature for 18 h to give the corre-
which is probably due to the robustness of the alkoxide sponding enyne 7. It was obtained as a light-yellow liquid after
purification by flash column chromatography on silica gel with
group in this medium, which makes the bidentate coordina-
1
tion of the enyne difficult.[17]
pentane/ethyl acetate (4:1) as the eluent (0.75 g, 86% yield).
NMR (CDCl
H
3
, 300 MHz): δ = 8.18 (d, J = 8.0 Hz, 2 H), 7.59 (d,
J = 8.0 Hz, 2 H), 5.89–6.00 (m, 1 H), 5.33 (dd, J = 17.0, 9.0 Hz, 2
1
3
3
H), 4.40 (s, 2 H), 4.15 (d, J = 5.0 Hz, 2 H) ppm. C NMR (CDCl ,
7
7
6.4 MHz): δ = 134.6, 132.4, 129.6, 123.5, 118.4, 90.7, 84.4, 85.3,
1.3, 57.8 ppm. MS (EI): m/z = 217.
Conclusions
Synthesis of Enyne 8
In conclusion, we could demonstrate the feasibility of the 4-Iodoanisole (1.16 g, 5 mmol), [PdCl (PPh ) ] (0.10 g, 3 mol-%),
2
3 2
3
Rh-catalysed PKR in glycerol, which shows that glycerol is CuI (0.057 g, 6 mol-%), Et N (1.4 mL, 10 mmol), 2-methyl-3-bu-
stable and suffers neither decarbonylation nor dehydrogena- tyn-2-ol (0.503 mL, 5.2 mmol), and freshly distilled thf (5 mL) were
introduced into a round-bottom flask with a Teflon inter-key under
tion under catalytic conditions. Interestingly, ligand-free Rh
argon. The resulting dark-brown reaction mixture was stirred at
systems are active and highly selective, depending on the
nature of the organometallic precursor. Because of the
30–35 °C for 3 h (up to complete consumption of the iodo deriva-
tive, which was monitored by GC analysis). The product corre-
sponding to the Sonogashira coupling was obtained as a light-
brown solid after the evaporation of thf, and it was purified by
flash column chromatography on silica gel by using dichlorometh-
Brønsted acid behaviour of glycerol, [Rh(μ-OMe)(cod)] , in
2
contrast to [Rh(μ-Cl)(cod)] , catalyses the efficient forma-
2
tion of bicyclo[3.3.0]octenones. In this medium, the alk-
oxide groups are labile, favouring both the generation of
1
3
ane as the eluent (0.84 g, 84% yield). H NMR (CDCl , 300 MHz):
vacant positions, which allows for enyne coordination, and δ = 7.29 (d, J = 8.0 Hz, 2 H), 6.76 (d, J = 8.0 Hz, 2 H), 3.72 (s, 3
1
3
3
the stabilisation of intermediates thanks to the coordinating H), 1.53 (s, 6 H) ppm. C NMR (CDCl , 76.4 MHz): δ = 159.7,
behaviour of glycerol (Scheme 3), aspects required for the 133.6, 115.5, 114.5, 92.5, 82.3, 65.6, 55.3, 31.6, 31 ppm. MS (EI):
m/z = 190.11.
formation of the expected product. Further investigations
concerning the use of glycerol in metal-catalysed processes 4-(4-methoxyphenyl)-2-methylbut-3-yn-2-ol (0.76 g, 4 mmol), NaH
are currently in progress.
(144 mg, 6 mmol), allyl bromide (0.17 mL, 6 mmol), and freshly
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distilled thf (10 mL) were mixed at room temperature for 18 h to
give the corresponding enyne 8. It was obtained as a light-yellow
liquid after purification by flash column chromatography on silica
[2] a) P. T. Anastas, J. B. Zimmerman, Environ. Sci. Technol. 2003,
37, 94A–101A; b) P. T. Anastas, M. M. Kirchhoff, Acc. Chem.
Res. 2002, 35, 686–694; c) P. Anastas, J. Warner, in: Green
Chemistry: Theory and Practice, Oxford University Press, New
York, 1998.
gel by using pentane/ethyl acetate (5:1) as the eluent (0.85 g, 92%
1
yield). H NMR (CDCl
3
, 300 MHz): δ = 7.35–7.38 (d, J = 8.0 Hz,
[
3] See for example: a) W. Leitner, Acc. Chem. Res. 2002, 35, 746–
2
H), 6.81–6.85 (d, J = 8.0 Hz, 2 H), 5.94–6.06 (m, 1 H), 5.35 (d,
7
56; b) S. Liu, J. Xiao, J. Mol. Catal. A 2007, 270, 1–43; c) M.
J = 17.0 Hz, 1 H), 5.14 (d, J = 10.0 Hz, 1 H), 4.19 (d, J = 5.0 Hz,
Gómez, E. Teuma, J. Durand, C. R. Chim. 2007, 10, 152–177;
d) R. K. Henderson, C. Jiménez-González, D. J. C. Constable,
S. R. Alston, G. G. A. Inglis, G. Fisher, J. Sherwood, S. P.
Binks, A. D. Curzons, Green Chem. 2011, 13, 854–862; e) M. J.
Raymond, C. S. Slater, M. J. Savelski, Green Chem. 2010, 12,
3
2
7
7
H), 3.79 (s, 3 H), 1.58 (s, 6 H) ppm. 1 C NMR (CDCl
3
,
6.4 MHz): δ = 159.6, 135.9, 133.1, 116.3, 114.8, 113.6, 89.9, 84.2,
1.1, 65.6, 55.4, 29.2 ppm. MS (EI): m/z = 230.10.
General Procedure for Rh-catalysed PKR: 0.0125 mmol [Rh(μ-
1826–1834.
–
2
X)(COD)] (X = OMe: 6.05 mg; X = Cl , 6.05 mg) and, if appropri-
[4] For pioneering work, see: a) I. U. Khand, G. R. Knox, P. L.
ated, the corresponding ligand (0.025 mmol; TPPTS: 14.2 mg; rac-
BINAP: 15.6 mg) were dissolved in glycerol (5 mL) in a Fisher–
Porter bottle. The corresponding 1,6-enyne was then added
Pauson, W. E. Watts, J. Chem. Soc., Chem. Commun. 1971, 36–
36. For preliminary mechanistical discussion, see: b) P.
Magnus, L. M. Principe, Tetrahedron Lett. 1985, 26, 4851–
4854. For a first example of intramolecular reaction, see: c)
N. E. Schore, M. C. Croudace, J. Org. Chem. 1981, 46, 5436–
5438. For reviews, see: d) P. L. Pauson, Tetrahedron 1985, 41,
(0.5 mmol; 1: 162.5 mg; 2: 86.11 mg), and the argon atmosphere
was replaced by CO (0.5 bar). The mixture was then stirred at 80 °C
for the desired time. After completion, CO was released in the
hood, and extractions with dichloromethane were carried out (3ϫ
5855–5860; e) N. E. Schore, Org. React. 1991, 40, 1–90; f) S. E.
Gibson, N. Mainolfi, Angew. Chem. 2005, 117, 3082; Angew.
Chem. Int. Ed. 2005, 44, 3022–3037; g) H.-W. Lee, F.-Y. Kwong,
Eur. J. Org. Chem. 2010, 789–811; h) The Pauson–Khand Reac-
tion. Scope, Variations and Applications (Ed.: R. R. Torres),
Wiley-VCH, Weinheim, Germany, 2012.
1
0 mL). The organic phases were then concentrated under vacuum
1
and analysed by H NMR spectroscopy. The corresponding car-
bocyclisation product was isolated by following the reported pro-
cedure.
[
23]
[
5] For selected reviews, see: a) A. Corma, S. Iborra, A. Velty,
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-(4-Nitrophenyl)-7-oxabicyclo[3.3.0]oct-1-en-3-one (7a): The prod-
uct was obtained by a Rh-catalysed carbocyclisation from the en-
yne 7 by following the procedure described in the main text. The
bicyclo[3.3.0]octenone 7a was obtained as a colourless oil after pu-
rification by column chromatography on silica gel by using pent-
ane/ethyl acetate (2:1) as the eluent. H NMR (CDCl
1
3
, 300 MHz):
[
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2
001, 624, 73–87; b) E. Kim, I. S. Kim, V. Ratovelomanana-
5
3
3
1
.04 (d, J = 16 Hz, 1 H), 4.67 (d, J = 8.0 Hz, 1 H), 4.34 (t, 1 H),
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7989.
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.0 Hz, 1 H) ppm. C NMR (CDCl
3
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(
EI): m/z = 245.13.
-(4-Methoxyphenyl)-8,8-dimethyl-7-oxabicyclo[3.3.0]oct-1-en-3-one
8a): The product was obtained by a Rh-catalysed carbocyclisation
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2
(
[
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after purification by column chromatography on silica gel by using
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pentane/ethyl acetate (2:1) as the eluent. H NMR (CDCl
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,
3
8
1
1
00 MHz): δ = 7.23–7.26 (d, J = 8.0 Hz, 2 H), 6.92–6.95 (d, J =
.0 Hz, 2 H), 4.34 (t, J = 8.0 Hz, 1 H), 3.83 (s, 1 H), 3.47–3.53 (m,
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13
ppm. C NMR (CDCl
30.4, 123.1, 114.1, 78.9, 70.2, 55.5, 43.9, 39.2, 29.1, 24.1 ppm. MS
EI) m/z = 258.18.
3
, 125 MHz): δ = 208.2, 183.2, 160.1, 135.3,
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(
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[
12] pK (CH OH) = 15.5; pK (glycerol) = 14.4. W. L. F. Armarego,
a
3
a
Supporting Information (see footnote on the first page of this arti-
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ed., Elsevier, Oxford, 2009.
[13] The signals corresponding to glycerol (width at middle height
2
7 and 17 Hz) and methanol (width at middle height 14 Hz)
appear larger than those corresponding to the complexes
Ͻ5 Hz), which proves that the exchange proposed between the
Acknowledgments
(
This work was financially supported by the Centre National de la
Recherche Scientifique (CNRS) and the Université Paul Sabatier.
F. C. thanks the Région Midi-Pyrénées and CNRS for a PhD
grant. The authors thank Pierre Lavedan for the helpful NMR dis-
cussions.
two rhodium complexes is slower than that between methanol
and glycerol on the NMR time scale. However, for [Rh(μ-
Cl)(cod)] , the glycerol signals are sharper (width at middle
2
height less than 8 Hz, Figure S3).
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Received: May 22, 2013
Published Online: August 28, 2013
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim