Multicomponent synthesis of pyran-2-ylidene chromium(0) and tungsten(0) fischer carbene complexes

Article abstract of DOI:10.1021/om9009558

A new reaction between chromium(0) and tungsten(0) carbene complexes 1 and alkynyl esters or ketones 2 in the presence of NMO to yield pyran-2-ylidene complexes 3 has been explored. Here, we discuss the scope of the reaction and propose a plausible mechanistic pathway. The method is a new multicomponent approach for the synthesis of pyranylidene carbene complexes.

Full text of DOI:10.1021/om9009558

Organometallics 2010, 29, 1607–1611 1607
DOI: 10.1021/om9009558
Multicomponent Synthesis of Pyran-2-ylidene Chromium(0) and
Tungsten(0) Fischer Carbene Complexes
†
Beatriz Baeza, Luis Casarrubios,* Mar Gomez-Gallego, Miguel A. Sierra,* and
,†
†
,†
ꢀ
Montserrat Olivan
‡
ꢀ
†
´
ꢀ
´
Departamento de Quımica Organica, Facultad de Quımica, Universidad Complutense de Madrid,
´
ꢀ
Aragon, Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain
‡
28040 Madrid, Spain, and Departamento de Quımica Inorganica-Instituto de Ciencia de Materiales de
ꢀ
Received November 2, 2009
A new reaction between chromium(0) and tungsten(0) carbene complexes 1 and alkynyl esters or
ketones 2 in the presence of NMO to yield pyran-2-ylidene complexes 3 has been explored. Here, we
discuss the scope of the reaction and propose a plausible mechanistic pathway. The method is a new
multicomponent approach for the synthesis of pyranylidene carbene complexes.
Scheme 1
Cr(0) and W(0) Fischer carbene complexes can undergo multi-
step transformations in a single synthetic step. This ability, in
either intermolecular or intramolecular processes, within com-
plexes having an adequate structure, has been profusely used in
synthesis.1 However, the formation of a Fischer carbene com-
plex as a result of a multicomponent reaction is less common.2
In fact, most of the approaches to obtain group 6 Fischer car-
bene complexes still rely on the procedure reported by Fischer
and Maasbol nearly 50 years ago.1l,3
In the search for new forms of reactivity we devised a multi-
component approach to these compounds by combining a simple
Cr(0) or W(0) Fischer carbene complex with N-methylmorpho-
line-N-oxide (NMO) (able to generate a vacant coordination site
in the metal complex) and a conjugated alkyne. Thus, complex 1a
was reacted with ethyl propiolate 2a and NMO for 12 h. A dark
purple solid, 3a, was obtained in 16% yield (related to the incor-
poration of two molecules of propiolate 2a), together with ethyl
benzoate, the oxidation product derived from the starting car-
bene (75% related to starting complex 1a) (Scheme 1). The
1H NMR spectrum of the new complex 3a showed two signals
(7.86 ppm (d) CH, 6.23 ppm (d) CH), which indicated the loss of
the phenyl group. These data, together with the signals indicating
the presence of two different ethoxy groups in the molecule (4.88
(q, 2H, J=6.9 Hz), 4.43 (q, 2H, J=7.1 Hz), 1.61 (t, 3H, J=6.9
Hz), 1.43 (t, 3H, J=7.1 Hz)), were in full agreement with the
structure of pyranylidene complex 3a. This compound is formed
by incorporation of two molecules of propiolate 2a to the
Cr(CO)5 fragment, with the total loss of the carbene ligand in
complex 1a. In spite of the poor yield, the formation of complex
3a was an encouraging start for our multicomponent approach.
The structure of 3a was finally confirmed by X-ray diffraction
analysis of a crystal obtained after Hex/EtOAc crystallization
(Figure 1). The Cr-C(1) bond length (2.073(3) A) is similar to
the Cr-C bond distance in other chromium-pyranylidene com-
plexes.4 The C(1)-O(1) bond length of 1.414(4) A indicates the
lack of multiple bonding between the carbene carbon and the
pyran oxygen, while the O(1)-C(5) and C(5)-O(2) bond
lengths, 1.310(4) and 1.293(4) A, respectively, indicate substan-
tial multiple bonding in this complex. The C(2)-C(3), C(3)-
C(4), and C(4)-C(5) bond distances are 1.404(5), 1.351(5), and
1.391(4) A, respectively. All these values are in agreement with
the bonding situation described by the structures in Chart 1.
*Corresponding authors. E-mail: (L.C.) luis_casarrubios@quim.
ucm.es; (M.A.S.) sierraor@quim.ucm.es.
ꢀ
(1) For selected recent reviews: (a) Barluenga, J.; Fernandez-Rodrı
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M. A.; Aguilar, E. J. Organomet. Chem. 2005, 690, 539. (b) Gomez-Gallego,
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M.; Mancheno, M. J.; Sierra, M. A. Acc. Chem. Res. 2005, 38, 44. (c) Zhao, Y.;
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Wang, J. Synlett 2005, 2886. (d) Barluenga, J.; Santamaría, J.; Tomas, M. Chem.
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Rev. 2004, 104, 2259. (e) Dotz, K. H.; Jakel, C.; Haase, W.-C. J. Organomet.
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J. Organomet. Chem. 2001, 624, 5. (g) Sierra, M. A. Chem. Rev. 2000, 100,
3591. (h) de Meijere, A.; Schirmer, H.; Duetsch, M. Angew. Chem., Int. Ed.
2000, 39, 3964. (i) Barluenga, J.; Fananas, F. J. Tetrahedron 2000, 56, 4597.
(j) Herndon, J. W. Tetrahedron 2000, 56, 1257–1280. (k) Aumann, R. Eur. J.
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Kusama, H. J. Am. Chem. Soc. 2000, 122, 10226. (d) Kusama, H.;
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r
2010 American Chemical Society
Published on Web 03/05/2010
pubs.acs.org/Organometallics

1608 Organometallics, Vol. 29, No. 7, 2010
Baeza et al.
Chart 1
Pyran-2-ylidene Fischer complexes are versatile compounds5
that can be prepared from preformed carbene complexes by re-
action with pyridinium ylides,6 enol ethers,4a or 1,3-diketones.7
Alternatively, other methods rely on the generation of the
carbene complex in the reaction medium, from 1-lithio 1,3-
dienes8 or β-ethynyl R,β-unsaturated esters or amides5c,d,9
and further reaction with the adequate metal carbonyls. The
multicomponent reaction in Scheme 1 could be considered a
hybrid method to access this class of compounds.
The reactivity of alkynyl Fischer carbene complex 1b was
tested next in the same reaction conditions. It should be
noted that complex 1b has a C-C triple bond that could take
part in the assembling of the reaction products.10 However,
reaction of 1b and ethyl propiolate in the presence of NMO
yielded pure 3a (45% yield) together with ethyl 3-phenylpro-
piolate (Scheme 2). No other products incorporating the
(45%) were obtained when the molar ratio of the reactants
NMO/complex 1b/alkyne 2a was 1.8:1.2:1.0. Higher amounts
of ethyl propiolate 2a (which in principle should favor the
formation of 3a) changed the reaction outcome to produce
self-coupling products derived from the alkyne,11 and no
pyranylidene complex 3a was obtained in these conditions.
Other variations in the reaction conditions, such as the slow
addition of reagents, the change in the addition order, the use
of different solvents (Et2O, CHCl3), and changes in tempera-
ture, did not produce any improvement in the product yields.
Scheme 2
To fully demonstrate the origin of the ethoxy groups in the
pyranylidene complex 3a, a new experiment between carbene
complex 1b and methyl propiolate 2b was carried out under
analogous conditions (Scheme 2). The reaction yielded com-
plex 3b (59% yield). The presence of two methoxy groups
(4.44 (s 3H), 3.96 (s, 3H)) in the 1H NMR spectrum of this
compound unequivocally demonstrated the total loss of the
carbene ligand in the starting complex 1b and the incorpora-
tion of two molecules of the external alkyne to the Cr(CO)5
fragment into the final product.
Pyran-2-ylidene complex 3b was also obtained from styryl-
carbene complex 1d and methyl propiolate, and the analogous
tungsten pyran-2-ylidene complex 3c was obtained in 17%
yield from tungsten carbene complex 1c, demonstrating that
the reaction does not depend on the nature of the starting
carbene. However, when complex 1b was reacted with methyl
2-hexynoate 2c, no pyranylidene complex was detected, which
indicated the need of a terminal alkyne for the reaction to take
place (Scheme 3). A mixture of inseparable 3-phenylpropiolate
and unreacted 2c (83% mass recovery) was isolated after
workup and flash chromatography.
Figure 1. ORTEP drawing of 3a. Hydrogen atoms were
omitted for clarity.
former carbene ligand in 1b were detected in the reaction. The
best conditions for the reaction of 1b with ethyl propiolate
(7) (a) Szesni, N.; Weibert, B.; Fischer, H. Inorg. Chim. Acta 2006, 359,
€
€
617. (b) Aumann, R.; Komeier, M.; Roths, K.; Frohlich, R. Tetrahedron 2000, 56,
€
4935. (c) Yu, Z.; Aumann, R.; Frohlich, R.; Roths, K.; Hecht, J. J. Organomet.
€
Chem. 1997, 541, 187. (d) Aumann, R.; Meyer, A. G.; Frohlich, R. J. Am. Chem.
€
Soc. 1996, 118, 10853. (e) Aumann, R.; Meyer, A. G.; Frohlich, R. Organome-
~
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tallics 1996, 15, 5018. (f) Jordi, L.; Camps, F.; Ricart, S.; Vinas, J. M.; Moreto, J.
M.; Mejías, M.; Molins, E. J. Organomet. Chem. 1995, 494, 53. (g) Aumann, R.;
€
€
Komeier, M.; Roths, K.; Frohlich, R. Synlett 1994, 1041–1044. (h) Aumann, R.;
€
ꢀ
Roths, K.; Lage, M.; Krebs, B. Synlett 1993, 667. (i) Camps, F.; Moreto, J. M.;
~
Ricart, S.; Vinas, J. M.; Molins, E.; Miravitlles, C. J. Chem. Soc., Chem.
Commun. 1989, 1560. (j) Aumann, R.; Heinen, H. Chem. Ber. 1987, 120, 537.
(8) Wang, Q.; Zhang, W.-X.; Xi, Z. Organometallics 2008, 15, 3627.
(9) (a) Kusama, H.; Sawada, T.; Okita, A.; Shiozawa, F.; Iwasawa,
N. Org. Lett. 2006, 8, 1077. (b) Iwasawa, N.; Shido, M.; Maeyama, K.;
Kusama, H. J. Am. Chem. Soc. 2000, 122, 10226.
All the experimental data collected pointed to the initial
reaction of the starting carbene complex 1 and NMO with
formation of a (CO)5M L species in the reaction medium,
3
(10) The cycloadditon reactions of alkynylchromium(0) carbene
followed by extrusion of the former carbene ligand in its
complexes and alkynes are scarce. See: (a) Barluenga, J.; Garcı
ꢀ
´
´
a-Garcıa,
P.; Fernandez-Rodrı
´
guez, M. A.; Rocaboy, C.; Aguilar, E.; Andina, F.;
Merino, I. Chem.;Eur. J. 2007, 13, 9115. (b) He-Ping Wu, H.-P.; Aumann,
(11) (a) Ramachandran, P. V.; Rudd, M. T.; Reddy, V. R. Tetra-
hedron Lett. 2005, 46, 2547. (b) Wenkert, E.; Adams, K. A. H.; Leicht, C. L.
Can. J. Chem. 1963, 41, 1844. (c) Pollart, K. A. U.S. Patent 3,383,403;
Chem. Abstr. 1968, 69, P35475k.
€
R.; Frohlich, R.; Saarenketo, P. Chem.;Eur. J. 2001, 7, 700. (c) Fogel, L.;
Hsung, R. P.; Wulff, W. D.; Sommer, R. D.; Rheingold, A. L. J. Am. Chem.
Soc. 2001, 123, 5580. (d) Fr€uhauf, H.-W. Chem. Rev. 1997, 97, 523.

Article
Organometallics, Vol. 29, No. 7, 2010 1609
Scheme 3
oxidized form.12 The terminal alkyne should then coordinate
the (CO)5M L species and rearrange to form the allenylli-
dene intermediate 5, which by reaction with another mole-
cule of alkyne would finally yield the pyranylidene complex 3
(Scheme 4).13
the preformed 3-lithio ethylpropiolate failed to yield the ex-
pected pyranylidene complexes 3. Since the self-condensation
of propiolates in the presence of tertiary amines such as
DABCO or TMEDA is known,11 it can be thought that the
ethyl propiolate may self-couple in the presence of NMO to
form ethyl hex-2-(E)-en-4-yn-1,6-oate. This product may sub-
sequently react with (CO)5ML to yield the pyranylidene com-
plex. To discard this possibility, ethyl hex-2-(E)-en-4-yn-1,6-
oate was prepared following the literature procedure11 and
3
Scheme 4
reacted with (CO)5Cr THF. The ester was recovered un-
3
changed after 24 h at rt. Thus, the ester self-coupling followed
by cycloisomerization is not forming the final pyranylidene
complex, at least in the conditions used in this work.
In the search for new evidence of the reaction mecha-
nism, propargyl ketones were next tested. The reaction of
ketone 2d and complex 1b yielded exclusively a new
pyranylidene complex, 3d (24% isolated yield). It should
be remarked that complex 3d incorporated two different
fragments, one fragment coming from the ketone 2d and
the other from the ethyl phenyl propiolate arising from the
starting carbene (Scheme 5).
Scheme 5
To obtain evidence for this proposal, the reaction was
carried out by generation in situ of the active (CO)5Cr
species, either by treatment of (CO)6Cr with amine-N-oxides
(NMO, TMANO, pyridine-N-oxide) or by light irradiation
in the presence of coordinating solvents (THF, Et2O) or amines
(Et3N). In all cases tested, the reaction with alkynes 2 or with
The incorporation of ethyl 3-phenylpropiolate in pyrany-
lidene 3d after being extruded from the starting complex 1b
was demonstrated by adding an excess (3.5 equiv) of methyl
hex-2-ynoate together with complex 1b to the preformed
mixture of NMO and 1-phenylprop-2-yn-1-one 2d. In this
case 3d (13%) was obtained, together with the new complex
3e (4%), therefore demonstrating the sequential incorpora-
tion of the ketone and the ester in the final product. An
analogous experiment was performed by using ethyl propio-
late 2a instead of 2d, yielding exclusively complex 3a (13%)
(Scheme 6).
(12) Generation of coordination vacant sites by the action of TMA-
NO is well known: Matthews, S. L.; Heinekey, D. M. J. Am. Chem. Soc.
2006, 128, 2615.
(13) Two identical NMR experiments were run in an attempt to
detect intermediates in these reactions. Thus, in a 0.5 cm diameter NMR
tube were placed 15 mg (0.13 mmol) of NMO and 5.98 mg (0.071 mmol)
of methyl propiolate in 0.6 mL of THF-d8. The NMR tube was allowed
to stand at rt, and the NMR spectrum was registered at rt. After 5 min
the tube was cooled to 0 °C and a new 1H NMR spectrum was registered
at 0 °C. A 30 mg (0.086 mmol) amount of complex 1a was then added,
and 1H NMR spectra were registered every 5 min for 1 h at rt. Finally,
the 1H NMR spectrum was registered overnight. No intermediates were
observed in these reactions.

1610 Organometallics, Vol. 29, No. 7, 2010
Baeza et al.
Scheme 6
The results above are compatible with a new reac-
tion pathway involving the initial addition of the NMO to
the highly electrophilic carbene carbon of the complex 1,
Scheme 7
leading not to (CO)5Cr L but to a new intermediate, 6, having
3
a highly nucleophilic chromium center.14 The attack of this
nucleophilic center to the alkyne 2 would yield a new inter-
mediate, 7, from which fragmentation and intramolecular
hydrogen transfer would lead to extrusion of the ester,
N-methylmorpholine, and the complex 5. This product will
evolve to the vinylidene intermediate 8 by Michael-type addi-
tion to a new alkyne (clearly in this step the presence of other
alkynes in the reaction medium will yield mixed products).
Complex 8 renders the final pyranylidene complex 3 by ring
closure of intermediate 9, formed upon protonation of 8
(Scheme 7). The aromatic nature of pyranylidene complexes
3 (represented by the contribution of the pyrilium form to the
description of the molecule) should be the driving force of the
process. Other N-oxides such as TMANO or pyridine-N-oxide
did not yield pyranylidenes due to their higher reactivity, which
probably breaks the M-C bond in intermediate 6 prior to the
nucleophilic attack to the external alkyne.
In conclusion, in this paper we describe a new method for the
formation of pyran-2-ylidene Fischer carbene complexes through
a multicomponent reaction. The addition of the NMO to the
carbene carbon of the starting carbene complex promotes the
nucleophilic cascade of reactions leading to the final products.
While the final yields are only acceptable, the sequential reported
procedure forms four bonds in a single step, leading to new
carbene complexes that are not easily available by other means.
The reaction is applicable to aryl-, styryl-, and ethynylchromium-
(0) and tungsten(0) Fischer carbene complexes.
anhydrous solvents from a Pure Solvent PS-MD-5 apparatus.
Commercial reactants were used without previous purification.
Chemical yields for products 3 are given related to starting
materials 2. NMR spectra were registered in a Bruker 300 AC
(300.01 MHz) at room temperature using CDCl3 as solvent.
Chemical shifts are given in ppm relative to CHCl3 (7.27 ppm)
for 1H NMR and CDCl3 (77.0 ppm) for 13C NMR. IR spectra
were registered in a Bruker TENSOR 27 apparatus (7500-370
cm-1) with 1 cm-1 resolution. ESI-HRMS spectra were re-
corded in a QTOF 6520 Agilent Technologies apparatus. All
attempts to obtain correct analytical data of pyranylidene
complexes 3 meet with no success. Even running two successive
analyses (with an intermediate test for the analyzer) of the same
Experimental Section
General Procedures. All reactions were carried out under
an Ar atmosphere using standard Schlenk techniques and
(14) (a) Imwinkelried, R.; Hegedus, L. S. Organometallics 1988, 7,
702. (b) Semmelhack, M. F.; Lee, G. R. Organometallics 1987, 6, 1839.
(c) Licandro, E.; Maiorana, S.; Manzotti, R.; Papagni, A.; Perdicchia, D.;
Pryce, M.; Tiripicchio, A.; Lanfranchi, M. Chem. Commun. 1998, 383.
(d) Bouaucheau, C.; Parlier, A.; Rudler, H. J. Org. Chem. 1997, 62, 7247.
€
(e) Kretschik, O.; Nieger, M.; Dotz, K. H. Chem. Ber. 1995, 128, 987.

Article
Organometallics, Vol. 29, No. 7, 2010 1611
complex gave totally unequal results. The reason for this
behavior is at present unknown.
with a solution of 483 mg (1.38 mmol) of complex 1b and 580 mg
(4.60 mmol) of methyl hex-2-ynoate 2c, in 5 mL of THF. The
reaction was stirred at room temperature until total consumption
of the starting complex 1b (overnight). After solvent evaporation
and purification by SiO2 chromatograpy (hexane to Hex/EtOAc,
1:1), 15 mg (4%) of pure 3e (dark orange solid) and 72 mg (13%) of
3d were obtained. 3e: 1H NMR (CDCl3, 700 MHz): δ 8.15-7.70
(m, 2H), 7.65-7.61 (m, 1H), 7.52-7.47 (m, 2H), 6.21 (s, 1H), 4.39
General Procedure for the Preparation of Pyranylidene Car-
bene Complexes 3. To a 0 °C suspension of NMO (1.80 mmol) in
anhydrous THF (15 mL) and under Ar was added 1.00 mmol of
the corresponding unsaturated alkyne 2. This mixture was
treated at 0 °C, under Ar, with 1.20 mmol of Fischer carbene
complex 1 in 5 mL of THF. The reaction was stirred at room
temperature until total consumption of the starting materials
(TLC). The solvent was removed under reduced pressure and
the crude purified by SiO2 chromatography (Hex/EtOAc
mixtures). The yields of complexes 3 are given relative to starting
alkynes 2.
(s, 3H), 2.23 (bt, 2H), 1.56-1.47 (m, 2H), 0.85 (t, 3H, J = 7.3). 13
C
NMR (CDCl3, 175 MHz): δ 259.4, 222.6, 217.1, 194.2, 173.4,
157.8, 145.8, 137.3, 134.3, 128.9, 128.9, 98.2, 57.4, 35.4, 22.1, 13.8.
IR (film): ν 2053, 1913, 1594, 656 cm-1. ESI-HRMS m/z: calcd for
C21H15CrO8 [M - H]- 447.0178; found 447.0175.
Complex 3a. Following the general procedure, from 430 mg
(3.67 mmol) of NMO, 200 mg (2.04) of ethyl propiolate 2a, and
858 mg (2.45 mmol) of complex 1b and after SiO2 chromato-
graphy (hexane to Hex/EtOAc, 8:2), 180 mg (45%) of pure 3a was
obtained as a dark purple solid. 1H NMR (CDCl3, 300 MHz): δ
7.86 (d, 1H, J = 8.8 Hz), 6.23 (d, 1H, J = 8.8 Hz), 4.88 (q, 2H,
J = 7.1 Hz), 4.43 (q, 2H, J = 7.1 Hz), 1.61 (t, 3H, J= 7.1 Hz), 1.43
(t, 3H, J = 7.1 Hz). 13C NMR (CDCl3, 75 MHz): δ 272.3, 223.5,
217.4, 173.6, 167.0, 144.7, 138.5, 97.84, 68.4, 62.1, 14.3, 14.0. IR
Structural Analysis of Complex 3a. Crystals suitable for X-ray
diffraction were obtained by crystallization in hexane/EtOAc.
X-ray data were collected on a Bruker Smart APEX CCD
diffractometer equipped with a normal focus, 2.4 kW sealed
tube source (Mo radiation, λ = 0.71073 A) operating at 50 kV
and 40 mA. Data were collected over the complete sphere by a
combination of four sets. Each frame exposure time was 10 s
covering 0.3° in ω. Data were corrected for absorption by using
a multiscan method applied with the SADABS program.16 The
structure was solved by Patterson (Cr atom) and conventional
Fourier techniques and refined by full-matrix least-squares on
F2 with SHELXL97.17 Anisotropic parameters were used in the
last cycles of refinement for all non-hydrogen atoms. Hydrogen
atoms (except those of the pyranilidene, which were observed in
the difference Fourier maps and refined as free isotropic atoms)
were included in calculated positions and refined riding on their
respective carbon atoms with the thermal parameter related to
the bonded atoms. All the highest electronic residuals were
observed in close proximity of the Cr center and make no
chemical sense.
(film): ν 2057, 1908, 1585, 666 cm-1
.
Complex 3b. Following the general procedure, from 150 mg
(1.28 mmol) of NMO, 60 mg (0.71) of methyl propiolate 2b, and
300 mg (0.86 mmol) of complex 1b and after SiO2 chromato-
graphy (hexane to Hex/EtOAc, 8:2), 75 mg (59%) of pure 3b was
obtained as a dark violet solid. 1H NMR (CDCl3, 500 MHz): δ
7.89 (d, 1H, J = 8.7 Hz), 6.27 (d, 1H, J = 8.7 Hz), 4.44 (s, 3H),
3.96 (s, 3H). 13C NMR (CDCl3, 125 MHz): δ 274.1, 223.9, 217.7,
174.4, 167.7, 145.2, 138.9, 97.9, 58.4, 52.8. IR (film): ν 2057,
1908, 1585, 666 cm-1. ESI-HRMS m/z: calcd for C13H7CrO9
[M - H]- 358.9501; found 358.9508.
Complex 3c. Following the general procedure, from 145 mg
(1.24 mmol) of NMO, 68 mg (0.69 mmol) of 2a, and 400 mg (0.83
mmol) of complex 1c and after SiO2 chromatography (hexane to
Hex/EtOAc, 8:2), 30 mg (17%) of pure 3c was obtained as a dark
violet solid. 1H NMR (CDCl3, 300 MHz): δ 8.03 (d, 1H, J = 8.8
Hz), 6.33 (d, 1H, J = 8.8 Hz), 4.85 (q, 2H, J = 7.1 Hz), 4.43 (q,
2H, J = 7.1 Hz), 1.60 (t, 3H, J = 7.1 Hz), 1.42 (t, 3H, J = 7.1
Hz). 13C NMR (CDCl3, 75 MHz): δ 247.5, 203.8, 198.5, 173.2,
166.7, 146.2, 137.5, 128.7, 98.8, 68.6, 62.6, 14.3, 14.0. IR (film): ν
2061, 1914, 1726, 772 cm-1. ESI-HRMS m/z: calcd for
C17H15O11W [M þ CH3COO]- 579.0132; found 579.0144.
Complex 3d. Following the general procedure, from 405 mg
(3.46 mmol) of NMO, 250 mg (1.92 mmol) of ketone 2d,15 and
808 mg (2.30 mmol) of complex 1b and after SiO2 chromato-
graphy (hexane to Hex/AcOEt, 8:2), 228 mg (24%) of pure 3d was
Crystal data for 3a: C15H12CrO9, Mw 388.25, dark orange
prism (0.08 ꢀ 0.08 ꢀ 0.08), triclinic, space group P1, a 9.486(3)
A, b 9.511(3) A, c 10.054(3) A, R 100.853(6)o, β 113.551(5)o, γ
94.245(6)o, V 805.4(4) A3, Z 2, Dcalc 1.601 g cm-3, F(000) 396, T
100(2) K, μ 0.758 mm-1; 7391 measured reflections (2θ: 4-57°,
ω scans 0.3°), 3840 unique (Rint = 0.0923); min./max. transmn
factors 0.764/0.955. Final agreement factors were R1 = 0.0561
(2518 observed reflections, I > 2σ(I)) and wR2 = 0.1286; data/
restraints/parameters 3840/0/235; GoF = 0.929. Largest peak
and hole 0.930 and -0.782 e/A3.
Acknowledgment. Financial support from the MICINN
of Spain (project numbers CTQ2007-67730-C02-01/BQU
(to M.A.S.), CTQ2008-00810 (to M.O.), and Consolider
ꢀ
Ingenio 2010 CSD2007-00006), the Diputacion General de
Aragon (E35) (to M.O.), and the CAM (P2009/PPQ1634-
1
obtained as a red solid. H NMR (CDCl3, 300 MHz): δ 7.67-
ꢀ
7.24 (m, 10H), 6.24 (s, 1H), 4.89 (q, 2H, J = 6.8 Hz), 1.65 (t, 3H,
J = 6.8 Hz). 13C NMR (CDCl3, 75 MHz): δ 262.6, 222.9, 217.1,
194.8, 172.9, 153.7, 144.1, 137.4, 135.4, 133.4, 130.3, 129.7, 128.6,
128.3, 128.2, 98.7, 67.7, 14.5. IR (film): ν 2053, 1913, 1586, 657
cm.-1 ESI-HRMS m/z:calcdforC23H11CrO8 [M - Et]- 466.9859;
found 466.9852.
AVANCAT) (to M.A.S.) is acknowledged.
Supporting Information Available: Copies of the 1H and 13
C
NMR spectra for all compounds prepared through this work,
X-ray analysis and crystal structure determination, including
bond lengths and angles of compound 3a. This material is
available free of charge via the Internet at http://pubs.acs.org.
Complex 3e. To a suspension of 243 mg (2.10 mmol) of NMO
in anhydrous THF (5 mL) and under Ar was added 150 mg (1.15
mmol) of ketone 2d. The mixture was treated at 0 °C, under Ar,
(16) Blessing, R. H. Acta Crystallogr. 1995, A51, 33. SADABS: Area-
detector absorption correction; Bruker-AXS: Madison, WI, 1996.
(17) SHELXTL Package v. 6.10; Bruker-AXS: Madison, WI, 2000.
Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(15) Heasley, V. L.; Shellhamer, D. F.; Chappell, A. E.; Cox, J. M.;
Hill, D. J.; McGovern, S, L.; Eden, C. C. J. Org. Chem. 1998, 63, 4433.