Interaction of dihydropyridines with alkoxycarbene complexes of tungsten: Formation and use as cyclopropanation reagents of pyridinium ylide complexes

Article abstract of DOI:10.1016/S0022-328X(98)00673-1

Alkoxycarbene complexes of tungsten, e.g. (CO)₅W=C(CH₃)OEt (13) react with 1,2- and 1,4-dihydropyridines, to give, upon transfer of a hydride to the carbene carbon, elimination of ethanol, and readdition of pyridine to an unstable alkylidene complex (CO)₅W=C(H)CH₃ (22), pyridinium ylide complexes of the type (CO)₅W^--C(H)(CH3)Py⁺ (17). A second pyridinium ylide complex (CO)₅W-C(H)(CH₃)C₅H₇N (16), and a third dihydropyridinium complex (CO)₅W-C(H)(CH₃)C₈H₁₁N (15), resulting from the interaction of respectively 2,5-dihydropyridine and 5-isopropylidene-2,5-dihydropyridine with (CO)₅W=C(H)(CH₃) were also isolated and fully characterized by X-ray crystallography. The origin of the two latter complexes could be established. The new N-ylide complexes react with olefins to give cyclopropanes. Especially interesting, as far as the yields are concerned, is the interaction of highly nucleophilic olefins such as enamines with (CO)₅W^--C(H)PhPy⁺ (25) which leads to isomeric cyclopropylamines. The mechanism of their formation will be discussed.

Full text of DOI:10.1016/S0022-328X(98)00673-1

Journal of Organometallic Chemistry 567 (1998) 119–126
Interaction of dihydropyridines with alkoxycarbene complexes of
tungsten: formation and use as cyclopropanation reagents of
pyridinium ylide complexes
Blanca Mart´ın-Vaca, Henri Rudler *, Max Audouin, Muriel Nicolas, Thomas Durand-Re´ville,
Brice Vissie`re
Laboratoire de Synthe`se Organique et Organome´tallique, UMR 7611, Uni6ersite´ Pierre et Marie Curie, Tour 44-45, 4 place Jussieu,
75252 PARIS Cedex 5, France
Received 16 October 1997; received in revised form 5 January 1998
Abstract
Alkoxycarbene complexes of tungsten, e.g. (CO)5WꢀC(CH3)OEt (13) react with 1,2- and 1,4-dihydropyridines, to give, upon
transfer of a hydride to the carbene carbon, elimination of ethanol, and readdition of pyridine to an unstable alkylidene complex
(CO)5WꢀC(H)CH3 (22), pyridinium ylide complexes of the type (CO)5W− –C(H)(CH3)Py+ (17). A second pyridinium ylide
complex (CO)5W–C(H)(CH3)C5H7N (16), and a third dihydropyridinium complex (CO)5W–C(H)(CH3)C8H11N (15), resulting
from the interaction of respectively 2,5-dihydropyridine and 5-isopropylidene-2,5-dihydropyridine with (CO)5WꢀC(H)(CH3) were
also isolated and fully characterized by X-ray crystallography. The origin of the two latter complexes could be established. The
new N-ylide complexes react with olefins to give cyclopropanes. Especially interesting, as far as the yields are concerned, is the
interaction of highly nucleophilic olefins such as enamines with (CO)5W− –C(H)PhPy+ (25) which leads to isomeric cyclopropy-
lamines. The mechanism of their formation will be discussed. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Alkoxy carbenes; Tungsten; Dihydropyridines; Pyridinium ylide complexes; Cyclopropanations
1. Introduction
5 was obtained via the reaction of the corresponding
phenyl ethoxy carbene complex 4 with PhLi, followed
by an acid treatment [3], and the benzylidene tungsten
complex 7 was prepared both by Casey and Fischer
[4,5], by borohydride reduction of the corresponding
phenyl ethoxy carbene complex 4.
A way to stabilize organic carbenes 1 (Scheme 1) and
to allow their detection by physical methods, especially
by UV spectroscopy, is to react them, at low tempera-
ture with pyridine [1]. This interaction leads to pyri-
dinium ylides 3 the lifetime of which is much longer
than that of the starting carbenes. In contrast to most
organic carbenes, Fischer-type carbene complexes are
stable species, which can be easily handled at room
temperature (r.t.) [2]. Moreover, several alkylidene
complexes of tungsten and chromium could also be
prepared: thus diphenylethylidene complex of tungsten
However, both alkylidene complexes are less stable
than the corresponding starting complex. Whereas the
former could be handled at r.t., the latter was only
stable at low temperature. Stabilization of both com-
plexes could however be achieved by their reaction with
triphenylphosphine, which gave the corresponding
phosphonium ylides (e.g. 7“8) [4].
* Corresponding author. Tel.: +33 44 276197; fax: +33 44
277089; e-mail: rudler@ccr.jussieu.fr
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00673-1

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The purpose of this paper is to describe a new
general method for the preparation and stabilization of
alkylidene complexes of tungsten(0), as pyridinium
ylide complexes, and to demonstrate that these com-
plexes can be used as synthons for the cyclopropana-
tion of olefins.
Thus, when 1,2-dihydropyridine 12, prepared by this
procedure, was added at 0°C to an ethereal solution of
(CO)5WꢀC(OEt)CH3 (13), a change of the colour from
yellow to orange rapidly took place [8]. After 1 h, most
of the starting complex had reacted, and four new
complexes could be detected by TLC, as difficult to
separate pairs of products. Careful silica gel chro-
matography allowed nevertheless the separation and
characterization of the new complexes. The less polar
complex was given structure 14, the known (pentacar-
bonyl) tungsten pyridine complex [9]. The second com-
plex, isolated in a 8.5% yield, agreed with structure 15,
a 5-isopropylidene-2,5-dihydropyridinium ylide com-
plex of tungsten, on the grounds of its spectroscopic
data (Table 1), and confirmed by X-ray spectroscopy
(Fig. 1).
2. Results and discussion
Alkoxycarbene complexes of the Fischer-type can be
compared, as far as some of their reactions are con-
cerned, to carbonyl derivatives, e.g. ketones or esters.
Two typical transformations which confirm this anal-
ogy are the aminolysis of alkoxycarbene complexes
which leads to aminocarbene complexes [6], the analogs
of amides, and their reduction with hydrides, which
The third complex, isolated in a 20% yield, had
structure 16, again a complex of a 2,5-dihydropyridine
as shown by its X-ray structure on Fig. 2. Finally, to
the most polar complex, the main product of the reac-
tion (50%) was given structure 17, the ethylidene pyri-
dinium ylide of tungsten pentacarbonyl. Its ORTEP
view is shown on Fig. 3. The most important bond
distances and bond angles of these three complexes are
shown in Table 1.
gives rise to tungstates (CO)5W− –C(H)(OR)(R) M+
[4].
It is known that carbonyl compounds can be reduced
by dihydropyridines to alcohols, a reaction which is
well documented in biochemistry (Scheme 2). In order
to further the analogy between carbene complexes and
carbonyl compounds, we explored the possibility of
using dihydropyridines as reducing agents for alkoxy-
carbene complexes.
According to the literature, protected 1,2-dihydropy-
ridine 10 is easily prepared as a single isomer, by low
temperature reduction of pyridinium chloroformate 9
with NaBH4 [7]. Removal of the protecting group is
achieved by treatment with excess MeLi, followed by
protonation.
Scheme 1.

B. Mart´ın-Vaca et al. / Journal of Organometallic Chemistry 567 (1998) 119–126
121
Table 1
13
1H and C-NMR data, crystallographic data and bond distances (A) and angles (°) for complexes 15, 16 and 17
˚
Complex
NMR data
1H H(1)
X-ray data
W–C(1)
l
l
13C C(1)
C(1)–C(2)
C(1)–N(1)
W–C(1)–C(2)
W–C(1)–N(1)
15
16
17
3.86
3.81
4.90
52.6
54.1
57.2
2.381(9)
2.34(2)
2.32(2)
1.51(1)
1.48(2)
1.35(3)
1.45(1)
1.54(2)
1.49(2)
113.2(6)
116.6(13)
122.8(16)
114.1(5)
109.2(11)
112.3(9)
2.1. Mechanism of the reduction reaction. Origin of the
new pyridinium ylide complexes
tion by pyridinium at oxygen followed by elimination
of ethanol and formation of the benzylidene complex 7
and pyridine. Interaction of the two latter species
would then lead to the observed pyridinium ylide com-
plex Scheme 3.
If the interaction of dihydropyridine with carbene
complexes follows the same pathway as with carbonyl
compounds, hydride transfer to the carbene carbon
should be observed. Although hydrogen is present on
the former carbene carbon of the three new complexes,
the course of the reduction reaction is more compli-
cated. In order to gain more insight into the new
reduction process, interaction of alkoxycarbene com-
plex 4 with N-methyl-1,4-dihydropyridine [10], which is
also a reducing dihydropyridine was examined: in that
case a pyridinium tungstate 6 (N+R4ꢀMePy+) was
isolated and characterized by NMR spectroscopy.
Treatment of 6 with CF3CO2H led to the expected
benzylidene complex 7 which could be stabilized as its
known triphenylphosphonium ylide 8 and fully charac-
terized. Thus, hydride transfer to the carbene carbon
takes indeed place; moreover, protonation by
CF3CO2H at the oxygen atom of the ethoxy group
induced the elimination of ethanol and the formation of
the benzylidene complex
2.2. Formation of 2,5-dihydropyridinium ylide
complexes
The fact that complexes 15 and 16 had the same
origin, complex (CO)5WꢀC(H)CH3 (22) and the lithium
amide of 1,2-dihydropyridine 11, was demonstrated in
the following way. The interaction of the protected
dihydropyridine 10 with two equivalents of MeLi leads
to the lithium amide 11 and acetone. Protonation of 11
leads to 1,2-dihydropyridine 12 (Eq. 3). However, 11
can be in equilibrium with the carbon–lithio compound
18: upon protonation 18 could indeed lead to 2,5-dihy-
dropyridine 19. Moreover, reaction of 18 with acetone
might also take place and lead, after dehydration to
5-isopropylidene-2,5-dihydropyridine 21.
Confirmation of this hypothesis was obtained by the
following simple reaction: addition of two equivalents
of CD3Li to the protected 1,2-dihydropyridine followed
by protonation, and reaction with complex 13 led inter-
The same set of reactions could thus take place in the
case of 1,2-dihydropyridine: first, a hydride transfer
which leads to the pyridinium tungstate then protona-
1
alia to complex 15D, in which, according to H and
13C-NMR spectra both methyl groups of the isopropyli-
dene substituent were deuterated.
Scheme 2.

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B. Mart´ın-Vaca et al. / Journal of Organometallic Chemistry 567 (1998) 119–126
Fig. 1. CAMERON projection of complex 15 with the atomic numbering scheme.
evaporation of the solvent and successive additions of
Thus, 1,2-dihydropyridine ‘reduces’ the alkoxy car-
excess dihydropyrane and CF3CO2H, a mixture of cis
and trans cyclopropane derivatives was formed and
isolated in 35% yield. Confirmation of their structure
bene complex 13 to the ethylidene complex 22 with
formation of pyridine. The reaction of 22 with pyridine
gives the pyridinium ylide complex 17, the main
product of the reaction. The reaction of 22 with the
more stable (less oxidable) 2,5-dihydropyridine 19 and
5-isopropylidene-2,5-dihydropyridine 21 leads, respec-
tively to the dihydropyridinium complexes 16 and 15.
Excess of MeLi reacts with acetone and suppresses the
formation of complex 15.
1
and stereochemistry was secured by H and 13C-NMR
and by NOE experiments.
2.3. Pyridinium tungstate 6 as a cyclopropanation
reagent
2.4. Pyridinium ylide complexes of tungsten as
cyclopropanation reagents for enamines
The interaction of the pyridinium tungstate 6 with
CF3CO2H, in the presence of triphenylphosphine led to
the phosphonium ylide complex 8, providing strong
evidence for the formation of the benzylidene complex
7. This could also be confirmed by its capture with
dihydropyrane. Thus, the reaction of N-methyl dihy-
dropyridine with complex 1 at −78°C led to a dark–
red solution of the pyridinium tungstate 6. After
In a previous publication [8], the transfer of the
alkylidene moieties of the pyridinium ylide complexes
to olefins was described. Especially rewarding were the
intramolecular reactions, and also the intermolecular
reactions involving electron-rich olefins such as enol
ethers. It was our feeling that enamines might be the
olefins of choice for successful intermolecular cyclo-
propanation reactions. And this was indeed the case. A

B. Mart´ın-Vaca et al. / Journal of Organometallic Chemistry 567 (1998) 119–126
123
Fig. 2. CAMERON projection of complex 16 with the atomic numbering scheme.
As far as the mechanism of these cyclopropanation
reactions is concerned, it is likely that enamines might
easily be able to displace the pyridine from the ylides,
with concomitant formation of a carbon–carbon bond,
pyridinium ylide complexes being here considered as
alkylating agents (Scheme 4). Reaction of the negatively
charged tungsten atom with the carbon of the intermedi-
ate iminium group, might then lead to a tungstacyclobu-
tane, a direct precursor of the aminocyclopropanes.
series of enamines [11], derived from cyclopentanone
and cyclohexanone, reacted with complex 25 at r.t. and
within the space of 1 h, to give high yields of the
corresponding cyclopropylamines as mixtures of iso-
mers. These were easily separated by silica gel chroma-
trography. To the less polar products were given
structures 26, 28 and 30 on the grounds of NMR
experiments, whereas 27, 29 and 31 had the opposite
stereochemistry. Cyclopropylamines had already been
obtained from enamines and precursors of carbenes by
other methods: however, transfer of the benzylidene
carbene has to the best of our knowledge not been
described [12].
3. Conclusion
The analogy between alkoxycarbene complexes of

124
B. Mart´ın-Vaca et al. / Journal of Organometallic Chemistry 567 (1998) 119–126
Fig. 3. CAMERON projection of complex 17 with the atomic numbering scheme.
tungsten and carbonyl compounds has been fruitfully
applied to the reduction of carbene complexes with
dihydropyridines: the reaction which is observed leads
to a new class of alkylidene complexes of tungsten(0),
which are stabilized as soon as they are formed by
pyridine to give pyridinium ylide complexes.
dried by distillation from a drying agent: THF and
Et2O from Na/benzophenone; CH2C12 from CaH2 and
P2O5. Enamines were prepared by published methods
[13].
4.1.1. 7-Phenyl-2-oxa-bicyclo(4.1.0)heptane
In the case of the phenyl-substituted complex, an
easy transfer of the carbene moiety was observed. This
transfer is especially efficient with electron-rich olefins
such as enol ethers and even more with enamines.
N-Methyldihydropyridine (0.22 g, 2.3 mmol) was
added to a solution of (CO)5WꢀC(OEt)Ph 4 (0.5 g, 1.14
mmol) in 25 ml of dichloromethane at −78°C. The
solution turned instantly to dark red. After warming to
0°C, the solvent was evaporated under vacuum to give
an oil which was washed with ice-cold hexane. The
residue was then disolved in 15 ml of dichloromethane
at −78°C and dihydropyrane (0.5 ml, 5.7 mmol) and
acid trifluoroacetic (0.26 ml, 3.4 mmol) were added.
The reaction mixture was warmed to r.t. slowly. Evapo-
ration of solvent followed by silica gel chromatography
gave with petroleum ether/dichloromethane (90/10) as
eluent complex 14 and with petroleum ether/diethyl
ether (90/10) 23 and 24 (0.07 g, 35%) as a melange of
isomers (93/7).
4. Experimental section
4.1. General methods
1H and 13C-NMR spectra were recorded on Bruker
AC-200 or AMX-400 instruments. Mass spectra are
m/z. Column chromatography was performed with
Merck silica gel (70–230 mesh) using various ratios of
dichloromethane/light petroleum ether and diethyl
ether/light petroleum ether as eluent. All reagents were
obtained from commercial suppliers and used as re-
ceived. Reactions were performed under an argon at-
mosphere in carefully dried glassware. Solvents were
Spectral data for 23 (major isomer): 1H-NMR
(CDC13) l 7.43–7.20 (m, 5H, Ph), 3.88–3.85 (dd, 1H,
Scheme 3.
Scheme 4.

B. Mart´ın-Vaca et al. / Journal of Organometallic Chemistry 567 (1998) 119–126
125
4H, NCH2), 2.09–2.01 (m, 1H, H3%), 1.99–1.97 (d, 1H,
J=4.3 Hz, H6), 1.91–1.84 (m, 1H, H5), 1.82–1.74 (m,
3H, H4, H5% and H3), 1.70–1.68 (m, 1H, H2), 1.44–1.38
(m, 1H, H4%). 13C-NMR (CDC13) l 128.4, 127.1, 125.0
and 121.4 (Ph), 67.3 (OCH2), 60.1 (C1), 49.6 (NCH2),
33.1 (C6), 31.6 (C2), 29 3 (C5), 28.5 (C4), 23.5 (C3).
J=6,6 Hz, H,), 3.51–3.45 (m, 1H, H3), 3.33–3.21 (m,
1H, H3%), 2.02–1.92 (m, 2H, H5 and H5%), 1.88–1.85 (m,
1H, H7), 1.33–1.24 (m, 1H, H6), 1.17 (m, 1H, H4), 0.57
(m, 1H, H4%). 13C-NMR (CDC13) l 131.8, 128.4, 126.2
and 121.6 (Ph), 64.8 (C3), 53.1 (C1), 23.3 (C7), 22.8
(C4), 17.5 (C5), 13.7 (C6). HRMS calc. (obsd) for
C12H14O+ 174.1044 (174.1044).
1
Spectral data for 29: H-NMR (CDC13) l 7.32–7.21
(m, 5H, Ph), 3.75–3.73 (m, 4H, OCH2), 2.91–2.86 (m,
2H, CH
6 H–N–CH6 H), 2.75–2.70 (m, 2H, CHH6 –N–
4.1.2. 1-[6-Phenyl-bicyclo(3.1.0)hex-l-yl]-piperidine
This was obtained from complex 25 (0.4 g, 0.88
mmol) and 1-cyclopent-1-enyl-piperidine (0.5 g, 3.3
mmol) in 10 ml of dichloromethane at r.t. for 1 h.
Evaporation of the solvent followed by silica gel chro-
matography first gave with petroleum ether/
dichloromethane (90/10) as eluent complex 14 as
yellow cristals (0.2 g, 60%), and then with petroleum
ether/diethyl ether (98/2) as eluent 26 (trans) as an oil
(0.05 g, 24%) and (90/10) 27 (cis) as an oil (0.09 g,
46%).
CHH), 2.29–2.27 (d, 1H, J=8.7 Hz, H6), 2.06–1.97
6
(m, 1H, H3), 1.96–1.86 (m, 1H, H5), 1.71–1.69 (m, 1H,
H2), 1.68 1.60 (m, 2H, H3% and H5%), 1.40–1.32 (m, 1H,
H4), 0.15–0.02 (m, 1H, H4%). 13C-NMR (CDCl3) l
137.6, 128.9, 128.3 and 126.Ph), 67.5 (OCH2), 59.1
(C1), 50.1 (NCH2), 33.3 (C6), 29.9 (C2), 25.3 (C5), 22.6
(C4), 21.2 (C3). HRMS calc. (obsd) for C16H21NO+
243.1623 (243.1623).
4.1.4. 4-[7-Phenyl-bicyclo(4.1.0)hept-1-yl]-morpholine
This was obtained from complex 25 (0.5 g, 1 mmol)
and 4-cyclohex-1-enyl-morpholine (0.85 g, 5 mmol) in
10 ml of dichloromethane at r.t. for 1 h. Evaporation
of the solvent followed by silica gel chromatography
first gave with petroleum ether/dichloromethane (90/
10) as eluent complex 14 as yellow crystals (0.1 g,
30%), and then with petroleum ether/diethyl ether (98/
2) as eluent 30 (trans) as an oil (0.075 g, 30%) and
(90/10) 31 (cis) as an oil (0.05 g, 18%).
1
Spectral data for 26: H-NMR (CDC13) l 7.20–7.03
(m, 5H, Ph), 2.36 2.27 (m, 4H, N–CH2), 1.97–1.89 (m,
1H, H3), 1.82 (d, 1H, J=4.6 Hz, H6), 1.78–1.73 (m,
1H, H5), 1.68–1.59 (m, 3H, H4, H5, and H3), 1.53–1.51
(m, 1H, H2), 1.31–1.18 (m, 7H, H4, N–CH2–CH2
N–CH2–CH2–CH
2). 13C-NMR (CDC13) l 139.9,
128.2, 126.9, 124.6 (Ph), 60.8 (C1), 50.7 (N–CH2), 33.9
(C2), 31.7 (C6), 27.5 (C5), 26.3 (N–CH2–CH2), 24.8
(N–CH2–CH2–CH2), 23.3 (C3), 21.5 (C4).
Spectral data for 27: H-NMR (CDC13) l 7.32–7.21
(m, 5H, Ph), 2.87–2.82 (m, 2H, CHH–N–CHH),
2.69–2.64 (m, 2H, CHH–N–CHH), 2.29–2.27 (d, 1H,
J=9 Hz, H6), 2.06–1.98 (m, 1H, H5), 1.95–1.86 (m,
1H, H3), 1.70–1.57 (m, 7H, H5%, N–CH2–CH2, H3%,
), 1.37–
6 ,
6
6
6
1
Spectral data for 30: H-NMR (CDC13) l 7.34–7.12
1
(m, 5H, Ph), 3.51–3.48 (m, 4H, OCH2), 2.55–2.51 (m,
4H, NCH2), 2.16–2.09 (m, 1H, H6%), 1.99–1.90 (m, 1H,
H4), 1.80–1.71 (m, 2H, H7 and H4%), 1.67–1.60 (m, 1H,
H6), 1.49–1.21 (m, 5H, H2, H3, H3%, H5 and H5%).
13C-NMR (CDC13) l 129.9, 128.0, 127.2 and 125.1
(Ph), 67.3 (OCH2), 50.3 (C1), 48.4 (NCH2), 36.5 (C7),
28.2 (C2), 24.1 (C6), 22.5 (C5), 22.4 (C4), 21.3 (C3).
6
6
6
6
6
H2), 1.50–1.45 (m, 2H, N–CH2–CH2–CH2
6
1.28 (m, 1H, H4), 0.13–0.00 (m, 1H, H4.). 13C-NMR
(CDC13) l: 138.1, 128.5, 128.3, 125.9 (Ph), 59.2 (C1),
512 (N–CH2), 33 4 (C6), 30.3 (C2), 26.4 (N–CH2–
1
Spectral data for 31: H-NMR (CDC13) l 7.22–7.10
(m, 5H, Ph), 3.63–3.60 (m, 4H, OCH2), 2.69–2.66 (m,
4H, NCH2), 1.99–1.92 (m, 2H, H6 and H7), 1.85–1.75
(m, 2H, H3 and H3%), 1.38–1.26 (m, 2H, H2 and H6%),
1.06–1.01 (m, 1H, H4), 0.94–0.82 (m, 2H, H5 and H5%),
0.43–0.33 (m, 1H, H4%). 13C-NMR (CDC13) l 138.4,
135.6, 128.9 and 126.6 (Ph), 68.0 (OCH2), 49.1
(NCH2), 46.9 (C1), 32.9 (C7), 24.1 (C2), 23.1 (C5), 22.3
(C4), 21.8 (C3), 18.8 (C6). HRMS calc. (obsd) for
C17H23NO+ 257.1780 (257.1780).
C6 H2), 25.3 (N–CH2–CH2–CH2), 24.7 (C3), 22.7 (C4),
20.9 (C5). HRMS calc. (obsd) for C17H23N+ 241.1830
(241.1829).
4.1.3. 4-[7-Phenyl-bicyclo(3.1.0)hex-1-yl]-morpholine
This was obtained from complex 25 (0.4 g, 0.88
mmol) and 4-cyclopent-1-enyl-morpholine (0.5 g, 3.24
mmol) in 10 ml of dichloromethane at r.t. for 1 h.
Evaporation of the solvent followed by silica gel chro-
matography first gave with petroleum ether/
dichloromethane (90/10) as eluent complex 14 as
yellow crystals (0.16 g, 50%), and then with petroleum
ether/diethyl ether (98/2) as eluent 28 (trans) as an oil
(0.1 g, 50%) and (90/10) 29 (cis) as an oil (0.06 g,
30%).
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Spectral data for 28: H-NMR (CDC13) l 7.28–7.13
(m, 5H, Ph), 3.55–3.43 (m, 4H, OCH2), 2.52–2.47 (m,

126
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