Reaction of aminocarbene complexes of chromium with alkynes 9.: From nitrogen ylid complexes toward alkaloid frameworks

Article abstract of DOI:10.1016/S0022-328X(98)00672-X

Aminocarbene complexes of chromium having the general structure (CO)₅Cr=C(R)NR₁R₂ react with diphenylacetylene to give pyrrolinones as the result of the insertions of the alkyne, of CO and the migration of an alkyl group from nitrogen to a carbon atom in α or γ with respect to the nitrogen atom. The mechanism of this new reaction has been thoroughly investigated: a nitrogen ylid originating from the interaction of the nitrogen atom of the starting aminocarbene complex with the central carbon of the ketene formed by insertion of the alkyne and of CO into the aminocarbene complex, is a crucial intermediate in these reactions. This ylid complex, the structure of which could be established as 25, leads to the observed pyrrolinones upon thermolysis. Mechanisms involving radicals have been discarded on the grounds of the reaction of cyclopropylcarbinyl-substituted aminocarbene complexes 45a,b: no rearrangement of the cyclopropylcarbinyl group is observed upon its migration, as shown by the X-ray structure of the pyrrolinone 46b. Mechanisms involving ion pairs or the participation of the metal have also been eliminated. For that purpose, the X-ray structures of two complexes, 51 and 52, in which the metal is not bound to the phenyl ring of the migrating groups, have been established. Finally, concerted (l,5) sigmatropic migrations of the alkyl groups from nitrogen to the carbons of the five-membered heterocycle in 25 account best for the observed results. The role of the metal could also be determined by the examination of the reactivity of the metal-free N-ylides. No rearrangement similar to that observed for complexes 25 is observed; only products arising from the cleavage of the bond between nitrogen and the central carbon of the ketene were obtained. As an application of this original reaction of carbene complexes, the synthesis of 102, 103, 105 and 106 which are derivatives of the lycorane alkaloid will be described: the keypoint is the use of intramolecular insertions of alkynes into suitably substituted aminocarbene complexes of chromium 101 and 104.

Full text of DOI:10.1016/S0022-328X(98)00672-X

Journal of Organometallic Chemistry 567 (1998) 101–117
Reaction of aminocarbene complexes of chromium with alkynes 9.
From nitrogen ylid complexes toward alkaloid frameworks
Henri Rudler a,*, Andre´e Parlier a, Miche`le Rudler a, Jacqueline Vaissermann b
a 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
b Laboratoire de Chimie des Me´taux de Transition, URA 419, 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
Aminocarbene complexes of chromium having the general structure (CO)5CrꢀC(R)NR1R2 react with diphenylacetylene to give
pyrrolinones as the result of the insertions of the alkyne, of CO and the migration of an alkyl group from nitrogen to a carbon
atom in h or k with respect to the nitrogen atom. The mechanism of this new reaction has been thoroughly investigated: a nitrogen
ylid originating from the interaction of the nitrogen atom of the starting aminocarbene complex with the central carbon of the
ketene formed by insertion of the alkyne and of CO into the aminocarbene complex, is a crucial intermediate in these reactions.
This ylid complex, the structure of which could be established as 25, leads to the observed pyrrolinones upon thermolysis.
Mechanisms involving radicals have been discarded on the grounds of the reaction of cyclopropylcarbinyl-substituted aminocar-
bene complexes 45a,b: no rearrangement of the cyclopropylcarbinyl group is observed upon its migration, as shown by the X-ray
structure of the pyrrolinone 46b. Mechanisms involving ion pairs or the participation of the metal have also been eliminated. For
that purpose, the X-ray structures of two complexes, 51 and 52, in which the metal is not bound to the phenyl ring of the
migrating groups, have been established. Finally, concerted (l,5) sigmatropic migrations of the alkyl groups from nitrogen to the
carbons of the five-membered heterocycle in 25 account best for the observed results. The role of the metal could also be
determined by the examination of the reactivity of the metal-free N-ylides. No rearrangement similar to that observed for
complexes 25 is observed; only products arising from the cleavage of the bond between nitrogen and the central carbon of the
ketene were obtained. As an application of this original reaction of carbene complexes, the synthesis of 102, 103, 105 and 106
which are derivatives of the lycorane alkaloid will be described: the keypoint is the use of intramolecular insertions of alkynes into
suitably substituted aminocarbene complexes of chromium 101 and 104. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Aminocarbenes; Chromium; Alkyne insertions; N-ylide complexes
1. Introduction
these unstable species had to be synthesized in the
coordination sphere of the metal. This could be done
by the choice of a stable precursor complex.[1].
Let us examine the case of organic carbenes 1. Al-
though these unstable species can be detected by physi-
cal methods, stratagems had to be found in order to
increase their stability, by modification of their struc-
ture as soon as formed. A way to detect these species
easily by UV spectroscopy is to allow them to react
with pyridine at low temperatures, an interaction which
An early achievement of organometallic chemistry
was to make visible to the eye the structure of unstable
organic species, by their coordination to a suitably
substituted transition metal and by carrying out the
X-ray structure of the adduct. Quite often, however,
* Corresponding author. Tel.: +33 44276197; fax: +33 44277089;
e-mail: rudler@ccr.jussieu.fr
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00672-X

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H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
Scheme 1.
leads to new adducts, pyridinium ylids 2, yet not
isolable, the lifetime of which is nevertheless consider-
ably lengthened [2] (Scheme 1(A)).
However, a prominent example of the remarkably
stabilizing properties of transition metals came from the
work of E.O. Fischer who prepared, from a transition
metal coordinated CO group, stable carbene complexes
of the type 4 [3]. Later on, a few less stable complexes
of the type 5 could also be isolated [4–6].
Very recently, we discovered that pyridinium ylids of
the type 2 could also be stabilized by their coordination
to a transition metal and isolated as room temperature
stable complexes 3 [7]. Their synthesis relies on the
analogy which exists between alkoxycarbene complexes
of the type 4 and carbonyl compounds and was also
carried out in the coordination sphere of the metal:
reduction of alkoxycarbene complexes of chromium
and tungsten with dihydropyridines led indeed to stable
pyridinium ylid complexes 3. Therefore, a tremendous
increase of the stability is also observed in going from
1 to 3 (Scheme 1(A)).
prepared at low temperature or stabilized in the form of
complexes of the structure 7 [8–10]. Like carbenes, they
react even at low temperature, with pyridine or tertiary
amines to give very labile adducts, pyridinium or te-
traalkylammonium ylids 8, detectable by infra-red spec-
troscopy [11,12].
In the present review, we demonstrate that such
nitrogen ylids derived from ketenes can be synthesized
in the coordination sphere of chromium by the inser-
tion of alkynes into aminocarbene complexes of this
metal, and can be isolated in several cases as stable
complexes 9 via ketene complexes 7. As for 2, an
important increase in the stability is observed upon
coordination to a metal center (Scheme 1(B)). More-
over, it will be shown that the thermolysis of the ylid
complexes 9 leads to lactams by migration of an alkyl
group from the positively charged nitrogen to the nega-
tively charged carbon, a transformation which is remi-
niscent of the Stevens rearrangement of organic
nitrogen ylids.
The intramolecular version of this reaction will be
examined in detail and applied successfully to the syn-
thesis of elaborate heterocyclic compounds such as
derivatives of the lycorane alkaloids.
In contrast to carbenes, ketenes 6 are much more
stable and can, for some of them, be prepared, isolated,
and handled at room temperature. Others have to be

H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
103
Scheme 2.
2. Results and discussion
2.1. Interaction of tertiary amines with ketenes:
experimental and theoretical approaches
The interaction of tertiary amines with ketenes, in a
reversible way, leading to nitrogen ylid intermediates,
has been suspected in several reactions. Examples which
are well documented are the addition of chloral to
ketenes in the presence of a tertiary amine, of imines to
ketenes, the addition of alcohols to ketenes, leading to
optically active esters, in the presence of a chiral ter-
tiary amine (Scheme 2) [13–15]. However, the suspected
intermediates 10 could not even be detected by physical
methods. Molecular orbital calculations from this labo-
ratory confirmed however the existence, as labile inter-
mediates of such ylids. Important modifications of the
charges on the interacting species are observed with an
increase of the negative charge on oxygen and a de-
crease of the negative charge on nitrogen. Delocaliza-
tion of the negative charge is also observed on C-3, the
terminus of the ketene function [16].
Scheme 4.
alkoxycarbene complexes of chromium 11 react with
alkynes, to lead successively via a carbene complex 12
and a ketene complex 13, to a phenol 14. The spatial
proximity of the phenyl ring to the ketene function
allows an electrocyclization reaction to occur on the
intermediate 13. It is clear that the opposite geometry,
as in 16, would not lead to annulation products but
rather, via an oxonium ylid 17, to the alkoxyfurane 18,
a minor product which is indeed observed in this reac-
tion (Scheme 4).
In the case of aminocarbene complexes 19 bearing a
vinyl and more scarcely a phenyl group on the carbene
carbon, we [16,18] and others [19] demonstrated that
similar annulation reactions could also take place and
lead to aminophenols 22 via 20 and 21. However in
that case, the configuration 24 in which the tertiary
amine is cis to the metal, is of the highest interest since
the nitrogen atom is now in close proximity to the
central carbon atom of the ketene 24. The formation of
a five-membered N-ylid complex 25 should thus be
possible (Scheme 5).
Stabilization of such intermediates might be achieved
by two approaches:
“ By an intramolecular reaction, starting from an
amine tethered to a ketene, the distance between the
two functions being judiciously adjusted (Scheme 3).
“ By withdrawal of the negative charge on the terminal
carbon of the ketene, such as in 9, to render the
central carbon of the ketene more electrophilic.
2.2. Origin of the ketenes and the ketene complexes:
the benzannulation reaction
That ketenes and ketene complexes can be formed by
CO insertions into carbene complexes of transition
metals is well established. Of special interest for our
approach to nitrogen ylids are the mechanistic aspects
of the well known benzannulation reaction of alkoxy-
carbene complexes discovered by Do¨tz [17]. The present
status of this reaction as far as the mechanism is
concerned is the following: Aryl (and vinyl)-substituted
Scheme 3.
Scheme 5.

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H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
Scheme 6.
2.3. The unexpected reactions of alkyl and phenyl
substituted aminocarbene complexes with alkynes
from nitrogen to the h-carbon (36“37), akin to that
observed in the above reactions of aminocarbene com-
plexes (Scheme 6).
A way to avoid the annulation reaction is to start
from alkyl-substituted aminocarbene complexes. Al-
though less reactive than alkoxycarbene complexes to-
wards alkynes, aminocarbene complexes of chromium
undergo insertion reactions with alkynes at the reflux
temperature of benzene. Thus complex 26 led to two
pyrrolinones 27 and 28 upon its reaction with dipheny-
lacetylene [20]. The structure of these products, estab-
lished by X-ray crystallography for 27, confirmed the
insertion of the alkyne and of CO as in the benzannula-
tion reaction, but also the migration of the benzyl
group from nitrogen to the k-carbon for the main
product 27, or to the h-carbon for the minor product
28. A similar behavior was observed for pyrroline-sub-
stituted carbene complexes 29a,b,c. The same inser-
As minor pathways, migrations on the carbon and on
the oxygen of the carbonyl group were also observed in
some special cases (36“38+39) [23]. Applied to the
reaction of complex 26, a plausible mechanism might
indeed involve the formation and rearrangement of an
ylid complex 33, and lead by migration of the benzyl
group, to the observed pyrrolinones 27 and 28. Simi-
larly, complex 29 might give, after the insertion reac-
tion the N-ylid complex 35 (Scheme 7).
Opening of the five-membered unsaturated ring fol-
lowed by a carbon–carbon bond formation, would
then give the bicyclic compound 30.
This series of results is thus in strong agreement with
the intermediate formation of N-ylid complexes upon
insertions of alkynes and CO, into aminocarbene com-
plexes of chromium. Attempts were thus made to de-
tect, possibly to characterize, and to try to rearrange
such intermediates into lactams.
tions, accompanied by the cleavage of
a
carbon–nitrogen bond of the five-membered ring and
migration of the alkyl chain from nitrogen to the
h-position led to bicyclic pyrrolinones 30a,b,c even in
the case of complex 29c (R=Ph) [21].
2.5. Isolation and rearrangement of N-ylid complexes
obtained from aminocarbene complexes of chromium.
Confirmation of the postulated mechanism.
The aminocarbene complexes examined so far bore
on nitrogen either a benzyl group as in 26, or an allyl
group as in 29. It is known from investigations on the
Stevens rearrangement of organic N-ylids that the
propensity for the migration is very high for the allyl
and the benzyl groups, the ylid 36 being indeed very
unstable, even at room temperature. However, this
propensity is much lower for alkyl groups, falling al-
most to zero in the case of piperidine-substituted ylids:
in the latter case, cleavage of the ylid with liberation of
the tertiary amine is observed (Scheme 8) [24].
These unexpected products are most probably, as we
will see, the result of the formation and the rearrange-
ment of N-ylid complexes 33 and 35 originating from
the aminoketene complexes 32 and 34.
We reasoned therefore that the chance to isolate an
N-ylid complex from the reaction of an aminocarbene
complex with an alkyne would be the highest for
aminocarbene complexes derived from piperidine or
from dialkyl-substituted amines. And this was indeed
the case. Thus a series of aminocarbene complexes
40a,b,c derived from piperidine was prepared. The reac-
tion of 40a with diphenylacetylene in cyclohexane or
benzene led, after 12 h at reflux temperature, to the
formation of a yellow precipitate which appeared to be
unstable on silica gel (TLC) and to give a very polar
complex. Attempts to purify this precipitate by silica gel
2.4. Analogy with the Ste6ens rearrangement of organic
N-ylids
Migrations of alkyl groups from nitrogen to carbon
are well known in organic chemistry. They occur in the
Stevens rearrangement of nitrogen ylids of the type 36
[22].
Such ylids are easily prepared from tertiary h-
aminoketones via their ammonium salts, and undergo a
thermal rearrangement with migration of a substituent

H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
105
Scheme 7.
chromatography led indeed to a complex which accord-
ing to its physical data and to the X-ray crystallogra-
phy, was the chromium tricarbonyl complex of the
aminoacid 43, the hydrolysis product of the intermedi-
ate aminoketene complex 41.
ketene function as shown by the C(4)–N(1) bond dis-
tance, 1.590 A, the non-linearity of the former ketene
˚
function with an angle C(3)–C(4)–O(1) of 138°, and
the tetrahedral geometry at the nitrogen atom: the
interaction of this complex with water induces, in the
presence of acidic silica gel, the rupture of the C(4)–
N(1) bond with formation of the aminoacid complex
43.
The same type of N-ylid complexes could be isolated
from the piperidine-substituted carbene complexes
40b,c (RꢀCH3, Ph), the most stable ylid complex being
42c. Aminocarbene complexes derived from dialkyl-
Thus purification of the precursor of the aminoacid
by silica gel had to be avoided. Crystallization in anhy-
drous solvents appeared to be the method of choice for
its purification. After much effort, crystals suitable for
an X-ray structure determination could finally be
grown. Clearly, as shown in Fig. 1, the precursor of the
aminoacid is the N-ylid complex 42 and not the
aminoketene complex 41. A bond exists between the
nitrogen atom and the central carbon of the former
Fig. 1. ORTEP projection of complex 42c with the atom numbering
Scheme 8.
scheme.

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H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
amines (dimethylamine, methylcyclopropylamine) be-
haved similarly, and led to fairly stable ylid complexes.
Scheme 9.
the main product of the reaction arose from the migra-
tion from nitrogen to the k-carbon, even for N-ylides
derived from large cyclic amines. The question that
could be raised was thus about the mechanism of these
migrations: will it be radicalar, metal-assisted or con-
certed? or by ion pairs?
2.7. Reaction of the cyclopropylcarbinyl carbene
complexes 45a and 45b with diphenylacetylene:
migration without rearrangement of the
cyclopropylcarbinyl group
The point was therefore to know if these N-ylides
would undergo a rearrangement, akin to that observed
in the direct transformation of aminocarbene complexes
such as 26 and 29 into 27, 28 and 30.
Since the N-ylid proved to be stable up to the reflux
temperature of benzene, attempts were made to rear-
range them in boiling toluene: and indeed clean reac-
tions were observed leading in high yield to the
expected lactams, the structure of which was also confi-
rmed by X-ray crystallography (42c“44c).
A powerful tool for the detection of radicalar path-
ways in rearrangement reactions, is to use the cyclo-
propylcarbinyl substituent as the migrating group: the
cyclopropylcarbinyl radical ring-opening is indeed a
very fast reaction leading to the homoallyl radical
(Scheme 9) [25]. Thus, if such a radical were formed
during the rearrangement of the intermediate ylid com-
plexes, products bearing instead the butenyl group
should be detected, at least in part.
We synthesized thus carbene complexes 45a and 45b
by aminolysis of the corresponding alkoxycarbene com-
plexes with cyclopropylcarbinylamine. They were ob-
tained in, respectively, 70 and 65% yield. Reaction with
diphenylacetylene led in both cases to a mixture of
pyrrolinones 46a,b and 47a,b in, respectively, 29 and
5% yields, and 62 and 7% yields. However, no com-
pound bearing the butenyl group could be detected.
The rearrangement of these N-ylid complexes into
bridgehead lactams or pyrrolinones was of a general
scope. It is thus likely that the direct formation of
pyrrolinones upon insertion of alkynes into aminocar-
bene complexes, occurs also via the intermediary of
N-ylid complexes.
2.6. Rearrangement of the N-ylid complexes:
mechanistic aspects
The Stevens rearrangement of purely organic N-ylids
has been thoroughly studied. Depending on the nature
of the substituents, it was found to be concerted (for
allyl groups) or radicalar (for benzyl groups). In this
latter case, tight radical pairs are involved, since a
chiral carbon radical (C(H)MePh) was transferred with-
out racemization. A rearrangement via ion pairs has
also been discarded. Side reactions, in which migrations
to the carbon or to the oxygen atom of the carbonyl
group took place, were also observed.
Confirmation of the structure of these products and
especially of the presence of the cyclopropylcarbinyl
group was obtained by NMR spectroscopy, and the
location of the group that migrated by X-ray crystallog-
raphy carried out on 46b. The ORTEP projection is
shown in Fig. 2 with the most important bond distances
and bond angles in Table 4. As in the previous cases,
the cyclopropylcarbinyl group migrated from nitrogen
to the k-carbon. It is thus likely that a radicalar mecha-
nism can be excluded at least for the main pathway. In
As far as the rearrangement of the N-ylid complexes
is concerned, a general trend appeared. In most cases,

H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
107
Fig. 2. CAMERON projection of complex 46b with the atom numbering scheme.
agreement with the preceding finding, albeit less con-
vincing, is the behavior of complex 48, bearing on
nitrogen a chiral methylbenzyl group CHPhMe. Almost
complete retention (or complete inversion) at the chiral
center was observed in the insertion products 49, as
demonstrated by NMR spectroscopy [27].
group in h to the carbonyl, thus very close to the site of
the former carbene carbon and of the inserted CO group.
There was however an exception: insertion of dipheny-
lacetylene into complex 26 derived from N-methylbenzy-
lamine led to a Cr(CO)3 complex of pyrrolinones 27 in
which the metal is coordinated to the phenyl of the
transferred benzyl group: this might be an indication for
the involvement of the metal in the migration reaction.
If so, a similar behavior could be expected for complex
50, the Cr(CO)3 group ending up on the phenyl of the
homobenzyl group. However, this was not the case: the
X-ray structures of both pyrrolinones 51 and 52 confi-
rmed indeed that the Cr(CO)3 group is on the phenyl in
h to the carbonyl. Their ORTEP projections are shown
on Figs. 3 and 4, the most important bond distances and
angles being gathered in Tables 5 and 6.
2.8. Metal-assisted rearrangement
Since the metal is present from the beginning of the
reaction until the formation of the final products in
most of the examined reactions, a metal-assisted migra-
tion cannot be excluded and might even be a sound
hypothesis.
In most of the pyrrolinones isolated as Cr(CO)3
complexes, the metal is coordinated to the phenyl

108
H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
Fig. 3. CAMERON projection of complex 51 with the atom numbering scheme.
It is also interesting to notice at this point the
pyrrazoles are known to undergo thermal rearrange-
ments by (1,5)-sigmatropic migrations of a substituent
from the tetrahedral carbon center [28–30]. The migra-
tory group remains here continuously and covalently
bonded to the rest of the molecule as transfer from one
ring atom to another proceeds.
Such a process, occurring in a concerted manner,
could also take place in the case of the N-ylid com-
plexes described herein. Two clockwise (1,5)-sigmat-
ropic migrations would bring the alkyl group from
nitrogen to the carbon in h to the carbonyl group via
the carbonyl carbon, whereas a counterclockwise (1,5)
migration would lead to a product bearing the alkyl
group on the h-carbon with respect to nitrogen
(Scheme 10). Both experimental and theoretical results
are in agreement with such a proposal.
surprising formation of the pyrrolinone 53 in which the
CH2CH2Ph group is missing. This might be an indica-
tion for a radicalar process, with escape of the migrat-
ing radical. Such loss of migrating groups has
precedents both in this chemistry [26], in the case of a
migrating methyl group, and in the Stevens rearrange-
ment of benzyl-substituted N-ylides [24].
2.9. The concerted (1,5)-sigmatropic rearrangement
One of the resonance forms of the N-ylid complex is
25: it can be compared to a substituted cyclopenta-
diene.
Molecular orbital calculations on complex 25 confi-
rmed indeed that the rearrangement was not under
charge control but rather under orbitalar control, the
charges being localized on oxygen and on nitrogen,
whereas the largest coefficients of the HOMO are on
the k-carbon, the experimentally most often observed
site of migration.
Hexaalkylated cyclopentadienes like substituted

H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
109
Fig. 4. CAMERON projection of complex 52 with the atom numbering scheme.
2.10. Mechanism by ion pairs
same reaction as observed with water which led to the
aminoacid 43.
A mechanism by ion pair does not operate here, even
partially, since the rearrangement carried out in the
presence of methanol or in pure butanol did not lead to
ethers such as 54. Instead, cleavage of the C(4)–N(1)
bond took place with formation of esters 56, thus the
2.11. Role of the metal
Besides inducing the insertion of the alkyne and of
CO, the metal probably plays an important role in the
formation and the stabilization of the intermediate
N-ylid complexes. It is striking to notice that in all of
the stable N-ylid complexes isolated so far, the metal
is coordinated to a phenyl group located in h with
Scheme 10.

110
H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
respect to the carbonyl group. This benzylic h-carbon
bears an important amount of the negative charge due
to the interaction of the nitrogen atom with the cen-
tral carbon of the ketene, according to semi-empiricl
AM1 calculations [16]. Now it is also known that
benzylic carbanions are stabilized by the coordination
of the Cr(CO)3 group to the phenyl ring. It results
that, due to the presence of the metal, the reverse
reaction, the formation of the enaminoketene from the
N-ylid complex is unlikely.
A way to confirm this assumption would be either
to carry out a typical reaction of ketenes on the ylid
complexes 25, or to remove the metal from the N-ylid
complexes and to see whether the rearrangement reac-
tion would be suppressed.
Use of the second approach was also negative. The
main product of the reaction of the ylide complex 42c
with pyridine was the rearranged bridgehead lactam
61.
As far as the first option is concerned, ketenes are
known to give cycloaddition products with olefins;
however, when complex 25 was refluxed in benzene in
the presence of cyclopentadiene, no cycloaddition reac-
tion was observed. Instead a protonation-demethyla-
tion of the N-ylid leading to 58 took place.
Cyclopentadiene is thus an acid strong enough to pro-
tonate the ylid, its conjugated base being then able to
remove a methyl group from the positively charged
nitrogen atom [31].
An indirect method had thus to be found in order
to remove the metal without destroying the com-
plex. Protonation of the ylid complex takes place very
easily as exemplified by the behavior of the weak
acid cyclopentadiene (vide supra). Such a protona-
tion occurs also on silica gel, and can also be carried
out with trifluoroacetic acid, or with fluoroboric acid.
In this latter case, a stable complex could be isolated
as dark-red crystals and fully characterized by X-ray
crystallography. Protonation at the carbon h to ni-
In the case of the second option, a classical method
to remove a Cr(CO)3 group from an aromatic ring is
to oxidize the metal with oxygen under irradiation or
to heat the complex in the presence of pyridine. How-
ever, in the case of complex 42c, both methods led to
unexpected results [32]. Although the metal could be
removed by oxidation, a first reaction leading to a
complexed aminolactone complex 59 resulting from
the insertion of an oxygen atom between C(1) and
C(4) and cleavage of the C(1)–N(1) bond took place,
followed by a second oxidation in which the metal was
finally removed to give the aminolactone 60. Use of
the milder oxidation reagent dimethyldioxirane led to
the same clean results.
trogen took place giving
a very stable piperi-
dinium tetrafluoroborate 62. This reaction is rever-
sible since deprotonation of complex 62 with trie-
thylamine took place quantitatively, at room tempera-
ture.
Decoordination of the metal could be accom-
plished as above under oxygen with UV or sunlight
irradiation. The stepwise formation of two metal-free
piperidinium fluoroborates 63 and 64 was observed
[32], the first one being the expected metal-free
product, and the second one arising from 63 by a
known photochemical oxidative cyclization reaction
[33].

H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
111
and the central carbon of the former ketene: as
observed, easy solvolysis to the acid or the lactone
can take place.
2.12. Intramolecular insertion reactions
So far we have demonstrated that aminocarbene
complexes could be used for the synthesis of original
pyrrolinones and bridgehead lactams. More interest-
ing as far as the structure of the products is con-
cerned, will be the application of this chemistry to
intramolecular insertion reactions.
One of the simplest complexes which was submit-
ted to an intramolecular insertion reaction had struc-
ture 68 bearing thus a benzyl group, the propensity
for the migration of which is known to be high. Its
thermolysis in boiling benzene led to a mixture of
complexed and metal-free bicyclic compounds 69, 70
and 71, the structure of which could be established
by NMR spectroscopy and for complex 69, by X-ray
crystallography [34].
Scheme 11.
Since deprotonation of complex 62 with triethy-
lamine could be carried out at room temperature
with quantitative regeneration of the starting N-ylid
complex 42c, attempts to convert the metal-free pipe-
ridinium fluoroborate 63 into the metal-free N-ylid 65
were undertaken. Although the deprotonation reac-
tion took place as expected, the N-ylid was not ob-
tained. Instead, trace amounts of water converted the
assumed intermediate 65 into one of its hydrolysis
products, the aminolactone 66, whereas in the pres-
ence of ethanol, even at low temperature, the amin-
oester 67 was obtained.
Table 1
Crystal data for 46b C27H25NO
Formula weight
379.5
12.655(3)
18.802(5)
8.983(11)
90
91.86(8)
90
2136
˚
a (A)
˚
b (A)
˚
c (A)
h (°)
i (°)
k (°)
3
˚
V (A )
Z
4
Crystal system
Monoclinic
P 21/n
0.66
Space group
Linear absorption coefficient v (cm−1
)
Density z (g cm−3
Diffractometer
Radiation
)
1.18
Philips PW1100
Mo—Kh (u=0.71069
˚
A)
Scan type
ꢀ/2q
Scan range (°)
q Limits (°)
0.8+0.345 tgq
2–25
Temperature or measurement
Octants collected
Room temperature
−15,15; 0,22; 0,10
Nb of data collected
4153
Nb of unique data collected
Nb of unique data used for refinement
Rint
3632
According to this latter result the role of the metal
is double:
“ During the process of formation of these ylids com-
plexes, it activates the ketene for the nucleophilic
addition of the tertiary amine.
“ It then stabilizes the benzylic anion in the ylid com-
plex by release of negative charge. Removal of the
metal weakens the bond between the nitrogen atom
1541 (Fo)2\3|(Fo)2
0.019
0.0482
0.0483
No
263
−0.20
0.47
R=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SwFoꢀ
Rw=[Sw(ꢀFoꢀ−ꢀFcꢀ)2/SwFo2]1/2
Extinction parameter
Nb of variables
−3
˚
˚
Dzmin (e A
)
)
−3
Dzmax (e A

112
H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
ingly, a second tricyclic product 80 was also isolated in
The three compounds originate probably from a
12% yield. Its structure, close to that of 79, contains an
extra carbonyl group.
common, non-isolated intermediate 72, a nitrogen ylid
complex, the rearrangement of which, according to the
same mechanism as above, can give either 69 or 70, the
main products of the reaction, by migration of the
benzyl group from nitrogen to the k-carbon, or in the
case of 70, by migration to the h-carbon with respect to
the nitrogen atom.
As a second example, we choose complex 73 derived
from piperidine: its thermolysis should lead to a stable
piperidinium ylid complex if the insertion reaction fol-
lows the same pathway as for the intermolecular inser-
tion reactions. Therefore, two type of reactions were
carried out: the first one in toluene which led to a
mixture of three tricyclic compounds 74, 75, and 76 in
40% yield; the second one in cyclohexane, which gave a
new complex the spectroscopic data of which agreed
with structure 77, a tricyclic N-ylid complex. Its ther-
molysis in toluene gave the same series of tricyclic
lactams 74, 75, and 76 in 38% yield, as in the direct
insertion reaction [34].
This result is of importance and constitutes a strong
indication for a partial non-concerted rearrangement of
the intermediate N-ylid complex 81. Its formation
might be the result of a radicalar pathway (81“82)
with formation of an acyl radical 83, upon insertion of
CO, followed by a ring closure to 80. Such a sequence
has indeed recently been described in the chemistry of
alkyl radicals [35].
As far as the mechanistic points of the rearrangement
are concerned, the behavior of complex 78 derived from
azetidine, was of special interest. Its thermolysis did not
lead to the expected bridgehead lactam but to the
azatriquinane 79, probably for steric reasons. Interest-

H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
113
It might also be the result of a metal-mediated re-
arrangement, a nucleophilic ring-opening giving 84
followed by a cyclocarbonylation reaction (81“84“
80). This is thus the second example showing clearly
that depending on the nature of the substituents, the
rearrangement can follow several distinct pathways.
properties. The tricyclic skeleton which is found in
the lycorane alkaloids, a pyrrolochinoline 85, might
be obtained at least on paper, from aminocarbene
complexes of the general structure 86 via successive
insertion of the triple bond, of CO, formation of a
nitrogen-ylid complex, followed by its rearrangement
according to the retrosynthetic Scheme 11 (87“90)
[37].
2.13. Approach to the synthesis of alkaloid skeletons
In order to test the possibilities of such an ap-
proach to the pyrrochinoline skeleton, we synthesized
the carbene complex 92 from the corresponding lac-
tam 91 according to the method of Hegedus [38].
Thermolysis of complex 92 led to a mixture of two
tricyclic products 93 and 94 in, respectively, 18 and
49% yields. Their structures were assigned by the use
of two dimensional NMR spectroscopy.
Having demonstrated that the intramolecular ver-
sion of the alkyne insertion reaction into aminocar-
bene complexes could lead in good yields to
elaborate polycyclic compounds, we attempted to use
this new reaction for the synthesis of alkaloid skele-
tons related to lycorane [36]. Derivatives of this al-
kaloid have inter alia interesting anti-tumor
Table 2
Table 3
Crystal data for 51 C34H27NO4Cr
Crystal data for 52 C34H27NO4Cr,CH2Cl2
Formula weight
565.6
18.924(4)
9.100(1)
17.011(9)
90
94.43(4)
90
2921
Formula weight
650.5
˚
˚
a (A)
a (A)
10.982(5)
11.330(1)
14.803(5)
100.55(7)
95.26(2)
115.13(2)
1596
˚
˚
b (A)
b (A)
˚
˚
c (A)
c (A)
h (°)
i (°)
k (°)
h (°)
i (°)
k (°)
3
3
˚
˚
V (A )
V (A )
Z
4
Z
2
Crystal system
Monoclinic
C c
4.17
1.29
Crystal system
Triclinic
P-1
5.55
Space group
Space group
Linear absorption coefficient v (cm−1
)
Linear absorption coefficient v (cm−1
)
Density z (g cm−3
Diffractometer
Radiation
)
Density z (g cm−3
Diffractometer
Radiation
)
1.35
Philips PW1100
Mo—Kh (u=0.71069
Philips PW1100
Mo—Kh (u=0.71069
˚
˚
A)
A)
Scan type
ꢀ/2q
Scan type
ꢀ/2q
Scan range (°)
q Limits (°)
1.1+0.345 tgq
2–25
Scan range (°)
q Limits (°)
0.9+0.345 tgq
2–22.5
Temperature of measurement
Octants collected
Room temperature
−22,22; 0,10; 0,20
Temperature of measurement
Octants collected
Room temperature
−11,11; −12,11; 0,15
Nb of data collected
2852
Nb of data collected
4055
Nb of unique data collected
Nb of unique data used for refinement
Rint
2562
Nb of unique data collected
Nb of unique data used for refinement
Rint
3832
1524 (Fo)2\2|(Fo)2
1968 (Fo)2\2|(Fo)2
0.025
0.0598
0.0627
No
313
−1.01
0.88
0.0213
0.0569
0.0585
28
390
−0.45
0.45
R=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SwFoꢀ
Rw=[Sw(ꢀFoꢀ−ꢀFcꢀ)2/SwFo2]1/2
Extinction parameter
Nb of variables
R=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SwFoꢀ
Rw=[Sw(ꢀFoꢀ−ꢀFcꢀ)2/SwFo2]1/2
Extinction parameter
Nb of variables
−3
−3
˚
˚
˚
˚
Dzmin (e A
)
)
Dzmin (e A
)
)
−3
−3
Dzmax (e A
Dzmax (e A

114
H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
A further step towards the synthesis of the lycorane
Table 4
Selected bond lengths (A) and bond angles(°) for 46b
˚
skeleton was achieved by the synthesis and successful
thermolysis of complex 96. This complex was obtained
in several steps from the acid chloride 95. Heating of
this carbene complex in benzene led to the expected
products 97 and 98 in 43 and l9% yields, their struc-
tures being again ascertained by extended NMR
spectroscopies.
˚
Bond lengths (A)
O(1)–C(8)
N(1)–C(2)
C(1)–C(10)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(9)–C(10)
C(10)–C(101)
1.215(5)
1.452(6)
1.349(6)
1.506(6)
1.504(7)
1.508(7)
1.541(6)
1.471(6)
N(1)–C(1)
N(1)–C(8)
C(1)–C(11)
C(3)–C(9)
C(4)–C(6)
C(8)–C(9)
C(9)–C(91)
1.412(6)
1.358(6)
1.481(6)
1.537(6)
1.506(7)
1.542(6)
1.527(6)
Bond angles (°)
C(1)–N(1)–C(2)
C(2)–N(1)–C(8)
N(1)–C(1)–C(11)
C(4)–C(3)–C(9)
C(3)–C(4)–C(6)
C(4)–C(5)–C(6)
O(1)–C(8)–N(1)
N(1)–C(8)–C(9)
C(3)–C(9)–C(10)
C(3)–C(9)–C(91)
128.1(4)
120.9(4)
118.7(4)
113.4(4)
l2O.4(4)
60.0(3)
126.5(4)
107.8(4)
111.8(4)
114.8(4)
C(1)–N(1)–C(8)
N(1)–C(1)–C(10)
C(10)–C(1)–C(11) 130.0(4)
111.1(3)
111.3(4)
C(3)–C(4)–C(5)
C(5)–C(4)–C(6)
C(4)–C(6)–C(5)
O(1)–C(8)–C(9)
C(3)–C(9)–C(8)
C(8)–C(9)–C(10)
C(8)–C(9)–C(91)
C(1)–C(10)–C(9)
120.4(4)
60.1(3)
59.9(3)
125.7(4)
108.1(4)
101.6(4)
107.0(3)
108.2(4)
C(10)–C(9)–C(91) 112.5(4)
C(1)–C(10)–C(101) 129.1(4)
C(9)–C(10)–C(101) 122.4(4)
Finally, the precursor 101 which was supposed to
lead to the substituted lycoranes was synthesized from
the acid 99. Its thermolysis led to the sought-after
lycorane derivatives 102 and 103 in 44.5 and 30%
yields.
In order to keep the possibility to further modify the
structure of the insertion products, the carbene complex
104 bearing a trimethylsilyl group instead of a phenyl
group on the triple bond, was also synthesized.
Its thermolysis led to two compounds 105 and 106,
albeit in lower yield, one of the products having lost its
trimethylsilyl group during the silica gel purification
step [39].
Thus, important structural modifications of the start-
ing carbene complexes do not hinder the normal course
of the alkyne insertion reactions, the same sequence
being always observed: insertion of the alkyne, insertion
of CO, formation of an ylid complex, and rearrange-
ments with nitrogen to carbon migrations.
3. Conclusion
The examination of the reaction of aminocarbene

H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
115
Table 5
OEt (4 g, 12.3 mmol) and (cyclopropylmethyl)amine (1
ml, 11.9 ml) in diethyl ether (80 ml) at room tempera-
ture. The reaction is instantaneous. Evaporation of the
solvent followed by filtration of the residue through
short column of silica gel with petroleum ether/
˚
Selected interatomic distances (A) and bond angles (°) for 51
Interatomic dis-
tances (A)
˚
N(1)–C(1)
N(1)–C(7)
C(1)–C(5)
C(3)–C(4)
C(4)–C(41)
C(5)–C(51)
C(6)–C(61)
1.41(1)
1.36(1)
1.36(2)
1.52(2)
1.51(1)
1.48(1)
1.56(1)
N(1)–C(2)
O(1)–C(7)
C(1)–C(11)
C(3)–C(6)
C(5)–C(6)
C(6)–C(7)
1.45(1)
1.20(1)
1.49(1)
1.56(1)
1.55(1)
1.57(2)
methylene
chloride
(95/5)
as
eluent
gave
(CO)5CrꢀC(Ph)NH(C4H7) (3.12 g, 74%) as a yellow oil.
1
Spectral data: H-NMR (CDCl3) l (two isomers) 9.15
(s, 1H, NH, E), 8.71 (s, 1H, NH, Z), 7.46–6.80 (m, 5H,
Ar), 3.96 (q, 2H, NCH2, Z), 3.05 (q, 2H, NCH2, E),
1.26 (m, 1H, CH, Z), 1.06 (m, 1H, CH, E), 0.75–0.26
(m, 4H, CH2); 13C-NMR (CDCl3) l 281.41 (CrꢀC),
223.38, 217.32 (CO), 128.70, 128.59, 127.79, 126.77,
121.09, 119.04 (Ar), 58.51, 55.70 (NCH2), 10.45, 10.26,
4.08, 3.78 (CH, CH2). MS calcd for C16H13O5NCr, 351
(M+), found 351.
A solution of (CO)5CrꢀC(Ph)NH(C4H7) in THF (60
ml) was treated at −60°C with LDA (10.24 mmol) in
THF (20 ml). Then methyl iodide (1 ml, 15.9 mmol)
was introduced. After heating to room temperature, the
solvent was evaporated, the residue hydrolyzed and
extracted as usual. The residue was then chro-
matographed on silica gel. Elution with petroleum
ether/dichloromethane (95/5) gave complex 45b (2.4 g,
77%) as a yellow oil. Spectral data of 45b (mixture of E,
Z isomers):1H-NMR (CDCl3) l 7.42–6.68 (m, 5H, Ar),
4.20 (d, J=6.8 Hz, 2H, CH2, Z), 4.03 (s, 3H, CH3, E),
3.21 (d, J=6.8 Hz, 2H, CH2, E), 3.08 (s, 3H, CH3, E),
1.25 (m, CH, Z), 0.91 (m, CH, E), 0.85–0.11 (m, 4H,
CH2); 13C-NMR (CDCl3) l 274.51 and 273.34 (Cr.C),
224.10 and 217.40 (CO), 153.15, 152.36, 129.35, 128.70,
128.40, 126.89, 125.75, 119.23, 118.81 (Ar), 67.87 and
62.34 (NCH2), 49.04 and 43.09 (NCH3), 10.26, 10.07,
Bond angles (°)
C(1)–N(1)–C(2)
C(2)–N(1)–C(7)
N(1)–C(1)–C(11)
C(4)–C(3)–C(6)
C(1)–C(5)–C(6)
C(6)–C(5)–C(51)
C(3)–C(6)–C(7)
C(3)–C(6)–C(61)
C(7)–C(6)–C(61)
N(1)–C(7)–C(6)
125.8(9)
121.1(10)
121.3(9)
116.0(9)
107.4(10)
127.4(10)
108.2(9)
105.5(8)
110.2(9)
105.7(10)
C(1)–N(1)–C(7) 112.9(g)
N(1)–C(1)–C(5) 111.4(g)
C(5)–C(1)–C(11) 127.1(10)
C(3)–C(4)–C(41) 111.5(9)
C(1)–C(5)–C(51) 125.2(9)
C(3)–C(6)–C(5) 113.7(9)
C(5)–C(6)–C(7) 102.7(9)
C(5)–C(6)–C(61) 116.4(8)
N(1)–C(7)–0(1)
O(1)–C(7)–C(6) 128.4(10)
125.8(10)
complexes of chromium with alkynes, has been at the
origin of interesting results both on a mechanistic and
synthetic point of view. New polar arene tricarbonyl
chromium nitrogen ylids could be isolated and fully
characterized. They lead by an unexpected rearrange-
ment highly dependent on the presence of the metal, to
original heterocyclic compounds, the most elaborate
being derivatives of alkaloids of the lycorane type.
Work is in progress in using the same approach for the
synthesis of pyrrolizidine, lupinine and stemona alka-
loid skeletons.
4. Experimental
Table 6
˚
4.1. General methods
Selected interatomic distances (A) and bond angles (°) for 52
1H- and 13C-NMR spectra were recorded respectively
at 200 or 400 and 50 or 100 MHz. IR spectra were
recorded as solutions. Mass spectra are m/z. Column
chromatography was carried out with Merck silica gel
(70-230 mesh) using various ratios of ethyl acetate
(EtOAc)/light petroleum ether (PE) or dichloro-
methane/light petroleum ether as eluent. All reagents
were obtained from commercial suppliers and used as
received. Reactions were carried out under an argon
atmosphere in carefully dried glassware. Solvents were
dried by distillation from a drying agent: THF and
Et2O from Na/benzophenone; CH2Cl2 from CaH2.
Interatomic distances
O(1)–C(7)
N(1)–C(2)
C(1)–C(3)
C(1)–C(11)
C(4)–C(41)
C(5)–C(51)
C(6)–C(61)
1.222(9)
1.46(1)
1.53(1)
1.54(1)
1.50(1)
1.48(1)
1.49(1)
N(1)–C(1)
N(1)–C(7)
C(1)–C(5)
C(3)–C(4)
C(5)–C(6)
C(6)–C(7)
1.47(1)
1.351(9)
1.53(1)
1.55(1)
1.32(1)
1.52(1)
Bond angles (°)
C(1)–N(1)–C(2)
C(2)–N(1)–C(7)
N(1)–C(1)–C(5)
N(1)–C(1)–C(11)
C(5)–C(1)–C(11)
C(3)–C(4)–C(41)
C(1)–C(5)–C(51)
C(5)–C(6)–C(7)
C(7)–C(6)–C(61)
O(1)–C(7)–C(6)
123.2(6)
122.8(7)
100.9(6)
109.3(7)
109.9(6)
110.7(7)
121.9(7)
109.5(7)
121.4(7)
127.9(7)
C(1)–N(1)–C(7) 113.8(7)
N(1)–C(1)–C(3) 110.7(7)
C(3)–C(1)–C(5) 112.8(7)
C(3)–C(1)–C(11) 112.6(7)
C(1)–C(3)–C(4) 115.5(7)
C(1)–C(5)–C(6) 110.4(7)
C(6)–C(5)–C(51) 127.5(7)
C(5)–C(6)–C(61) 129.1(8)
O(1)–C(7)–N(1) 126.9(8)
N(1)–C(7)–C(6) 105.1(7)
4.2. Pentacarbonyl (N-methyl-cyclopropylcarbinyl)
benzylidene chromium (0) 45b
That compound was obtained from (CO)5CrꢀC(Ph)

116
H. Rudler et al. / Journal of Organometallic Chemistry 567 (1998) 101–117
(s, CH3), 2.83 (m, CH2). MS (DPCI, NH3) calcd for
C21H17NO5Cr+NH4: 433. Found: 433.
4.58, 4.31, 3.63 (CH, CH2). MS calcd for C17H15
O5NCr: 365 (M+), found 365.
4.3. Reaction of complex 45b with diphenylacetylene
4.5. Reaction of complex 50 with diphenylacetylene
A solution of complex 45b (2.2 g, 6.0 mmol) and
diphenylacetylene (1.6 g, 9 mmol) in benzene (50 ml)
was refluxed for 48 h. Evaporation of the solvent under
vacuum led to a residue which was refluxed in pyridine
(30 ml) for 24 h. Evaporation of the solvent followed
by silica gel chromatography of the residue gave first
with petroleum ether/ethyl acetate (90/10) as eluent 46b
(1.41 g, 62%) as a white solid which was recrystallized
from methanol-dichloromethane, mp 169°C; then with
petroleum ether/ethyl acetate (80/20) 47b (0.16 g, 7%)
Complex 50 (2.5 g, 6.0 mmol) was refluxed in ben-
zene (50 ml) in the presence of diphenyacetylene (2.35
g, 13.8 mmol) for 12 h. After evaporation of the
solvent, the residue was chromatographed on silica gel
in order to separate the two complexes 51 and 52 from
the organic products. Elution with PE/EtOAc (90/10)
gave fractions containing complex 51. Yellow solid. Mp
1
130°C; IR (CHCl3) 1970, 1890, 1690 cm−1; H-NMR
(200 MHz, CDCl3) l 7.43–6.78 (m, 15H, Ar), 6.18, (d,
1H, ArCr), 5.25 (m, 2H, ArCr), 4.93 (t, 1H, ArCr), 2.97
(s, 3H, Me), 2.58 (m, 4H, CH2CH2). Anal. Calc. for
C34H27NO4Cr (%): C, 72.21; H, 4.78; N, 2.48. Found:
C, 72.33; H, 4.82; N, 2.48. Then fractions containing
complex 52, isolated as an orange solid. Mp 90°C; IR
1
as an oil. Spectral data for 46b: H-NMR (CDCl3, 200
MHz) l 7.49–6.72 (m, 15H, Ar), 2.94 (s, 3H, NCH3),
2.40 (dd, 1H, CHPh), 2.12 (dd, 1H, CHPh), 0.65 (m,
1H, CH), 0.30–0.03 (m, 4H, 2CH2); 13C-NMR (CDCl3,
50 MHz) l 180.97 (CO), 141.38–122.15 (13 peaks, Ar),
60.51 (Cq), 38.14 (CH2), 28.24 (NCH3), 6.48, 3.89, 3.65
(cyclopropane). Anal. Calc. for C27H25NO (%): C,
85.45; H, 6.64; N, 3.69. Found: C, 85.47; H, 6.64; N,
3.61. Spectral data for 47b: 1H-NMR (CDCl3,
200MHz) l 7.42–6.64 (m, l5H, Ar), 2.73 (s, 3H,
NCH3), 2.10 (m, 2H, CH2), 0.53 (m, 2H), 0.40 (m, 1H),
0.06 (m, 1H), −0.10 (m, 1H); 13C-NMR (CDCl3, 50
MHz) l 170.50 (CO), 138.35–126.88 (12 peaks, Ar),
72.22 (Cq), 35.97 (CH2), 25.56 (NCH3), 4.73, 4.23, 4.12
(cyclopropane). HRMS calcd for C27H25NO (M+)
379.1936; measd 379.1934.
1
(CHCl3) 1970, 1895, 1675 cm−1; H-NMR (200 MHz,
CDCl3) l 7.34–6.70 (m, 15H, Ar), 6.21 (d, 1H, ArCr),
5.29 (m, 2H, ArCr), 5.03 (t, 1H, ArCr), 2.78 (s, 3H,
Me), 2.48–2.34 (m, 4H, CH2CH2). HRMS calc. for
C34H27NO4Cr (M+): 565.1345. Found: 565.1345.
4.6. Remo6al of Cr(CO)3 from complexes 51 and 52:
formation of the pyrrolinones 51a and 52a
All the fractions were then gathered, the solvent
evaporated under vacuum and the residue heated in
boiling pyridine for 12 h. Evaporation of the solvent
followed by chromatography gave with PE/CH2Cl2 (80/
20) diphenylindenone (0.05 g, 3%), then with PE/
EtOAc (97/3) diphenylindanone (0.06 g, 3.6%), with
PE/EtOAc (95/5) tetraphenylcyclopentadienone (0.020
g), with PE/EtOAc (90/10) compound 51a (1.10 g,
42.6%) as a white solid. Mp 162°C; NMR IR (200 Mhz,
CHCl3) l 7.51–6.83 (m, 20H, Ar), 3.03 (s, 3H, Me),
2.90 (m, 1H, CH), 2.59 (m, 2H, CH2), 2.30 (m, 1H,
CH); 13C-NMR (50 MHz, CDCl3) l 180.42 (CO),
141.67, 140.21, 133.24, 130.0–122.15 (Ar, CꢀC), 60.30
(Cq), 35.41 (Me), 30.94 (CH2), 28.42 (CH2). HRMS
calc. for C31H27NO (M+): 429.2091. Found: 429.2088.
Then with PE/EtOAc (85/15) compound 52a (0.15 g,
4.4. Pentacarbonyl (N-methyl-phenethyl) benzylidene
chromium (0) 50
This complex was obtained in two steps from pen-
tacarbonyl (ethoxy) benzylidene chromium (0) (3.3 g,
8.2 mmol) and phenethylamine (2.5 ml, 19.8 mmol) in
diethyl ether. Yellow solid (3.3 g, 67%); mp 35°C;
1H-NMR (200 MHz, CDCl3) l (E, Z mixture) 9.0 and
8.45 (bs, 1H, NH), 7.36–6.54 (m, 10H, Ar), 4.40, 3.45,
3.20, 2.84 (m, 4H, CH2CH2); 13C-NMR (50 MHz,
CDCl3) l 282.64 and 279.17 (CrꢀC), 223.38, 217.08
(CO), 149.45–119.0 (Ar), 54.16, 51.82, 35.93, 35.51
(CH2CH2).
MS
(DCPI,
NH3)
calcd
for
1
5.8%) as an oil; IR (CHCl3) 1690 cm−1; H-NMR (200
C20H15NO5Cr+NH4: 419. Found: 419. To the previ-
ous complex (3.2 g, 7.9 mmol) in THF (50 ml) at
−80°C was added LDA obtained from iPr2NH (0.9
ml) and BuLi (8.8 ml). The solution was then brought
to room temperature for 1 h, then cooled to −40°C
and excess methyl iodide added. Workup as usual and
purification on silica gel gave complex 50 (2.7 g, 82%)
Mhz, CDCl3) l 7.48–6.67 (m, 20H, Ar), 2.78 (s, 3H,
Me), 2.44 (m, 4H, CH2CH2); 13C-NMR (50 Mhz,
CDCl3) l 170.47 (CO), 155.96, 141.15, 137.84, 129.78–
126.24 (Ar, CꢀC), 71.50 (Cq), 33.38 (Me), 29.14 (CH2),
25.17 (CH2). HRMS calc. for C31H27NO (M+):
429.209. Found: 429.209. Elution with PE/EtOAc (80/
20) gave compound 53 (0.08 g, 4.1%) as a white solid.
1
as an oil. H-NMR (200 MHz, CDCl3) l (mixture of
1
Mp 198°C; H-NMR (CDCl3, 200 MHz) l 7.47–6.98
two E, Z isomers) 7.33–6.44 (m, 10 H, Ar), 4.45 (m,
CH2), 3.98 (s, CH3), 3.56 (m, CH2), 3.24 (m, CH2), 2.96
(m, 20H, Ar), 5.28 (s, 1H, CHPh), 2.90 (s, 3H, Me).

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117
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Accurate cell dimensions and orientation matrices
were obtained by least-squares refinements of 25 accu-
rately centered reflections. No significant variations
were observed in the intensities of two checked reflec-
tions during data collection. Complete crystallographic
data and collection parameters listed in Tables 1–3.
The data were corrected for Lorentz and polarization
effects. Computations were carried out by using the PC
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least-squares. All non-hydrogen atoms were anisotropi-
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lated positions. Selected bond distances and bond
angles are listed in Tables 4–6. The drawing of the
molecules was carried out with the program
CAMERON [43].
Fractional atomic coordinates, anisotropic thermal
parameters for non-hydrogen atoms, atomic coordi-
nates for H atoms, and complete lists of bond distances
and bond angles have been deposited at the Cambridge
Crystallographic Data Center. Copies of the data free
of charge can be obtained on application to the Direc-
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UK.
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