Palladium-induced intramolecular pyridine-allyl coupling reactions: Formation of N-bridgehead heterocycles with a stable C-N bond

Article abstract of DOI:10.1002/(SICI)1099-0682(199810)1998:10<1563::AID-EJIC1563>3.0.CO;2-P

In the presence of stoichiometric amounts of bis(acetonitrile)dichloropalladium(II) the ortho-alkenylpyridines 2-but-3′-en-1′-ylpyridine (1), 2-pent-5′-en-1′-ylpyridine (2), 2-hex-5′-en-1′-ylpyridine (3), 2-hept-6′-en-1′-ylpyridine (4) and 2-methyl-6-pent-4′-en-1′-ylpyridine (5) led to a mixture of coordination compounds such as 2-alken-1′-ylpyridine-kN:k²C-dichloropalladium(II) and bis(2-alken-1′-ylpyridine-kN)-dichloropalladium(II) together with 2-pent-4-ene-1′,3′-diylpyridine-kN:k ³C-chloropalladium(II) and 2-hex-4-en-1′,3′-diylpyridine-kN:K³C-chloropalladium(II) in the case of 2 and 3 respectively. The latter were quantitatively demetallated in the presence of an excess of triphenylphosphane to yield tris(triphenylphosphane)palladium(0), 2-vinyl-2,3-dihydroindolizinium chloride and 2-prop-1′-en-1′-yl-2,3-dihydroindolizinium chloride, respectively, by a regioselective addition of the pyridine unit onto the more congested terminal carbon atom of the allyl fragment.

Full text of DOI:10.1002/(SICI)1099-0682(199810)1998:10<1563::AID-EJIC1563>3.0.CO;2-P

FULL PAPER
Palladium-Induced Intramolecular Pyridine-Allyl Coupling Reactions:
Formation of N-Bridgehead Heterocycles with a Stable C–N Bond
Jaganaiden Chengebroyen, Mary Grellier, and Michel Pfeffer*
`
´
´
Laboratoire de Syntheses Metallo-induites, Universite Louis Pasteur,
4 rue Blaise Pascal, F-67070 Strasbourg, France
Fax: (internat.) ϩ 33-3/88454667
E-mail: pfeffer@chimie.u-strasbg.fr
Received April 24, 1998
Keywords: ortho-Alkenylpyridines / C–H Activation / Palladium / Pyridine-allyl coupling / Indolizinium derivatives
In the presence of stoichiometric amounts of bis(ace-
tonitrile)dichloropalladium(II) the ortho-alkenylpyridines 2-
but-3Ј-en-1Ј-ylpyridine (1), 2-pent-5Ј-en-1Ј-ylpyridine (2), 2-
hex-5Ј-en-1Ј-ylpyridine (3), 2-hept-6Ј-en-1Ј-ylpyridine (4)
and 2-methyl-6-pent-4Ј-en-1Ј-ylpyridine (5) led to a mixture
of coordination compounds such as 2-alken-1Ј-ylpyridine-
κN:κ2C-dichloropalladium(II) and bis(2-alken-1Ј-ylpyridine-
κN)-dichloropalladium(II) together with 2-pent-4-ene-1Ј,3Ј-
diylpyridine-κN:κ3C-chloropalladium(II) and 2-hex-4-en-
1Ј,3Ј-diylpyridine-κN:κ3C-chloropalladium(II) in the case of 2
and respectively. The latter were quantitatively
demetallated in the presence of an excess of triphenyl-
phosphane to yield tris(triphenylphosphane)palladium(0), 2-
vinyl-2,3-dihydroindolizinium chloride and 2-prop-1Ј-en-1Ј-
3
yl-2,3-dihydroindolizinium chloride, respectively, by
a
regioselective addition of the pyridine unit onto the more
congested terminal carbon atom of the allyl fragment.
Introduction
Scheme 1. ortho-Alkenyl pyridines (o-AlkPy)
The formation of an intramolecular CϪN bond between
an amine and an olefin activated in the presence of pal-
ladium complexes, has been extensively studied. Indeed,
Hegedus and co-workers[1] have shown that for primary and
secondary amines this amine-olefin coupling reaction,
yielding a new CϪN bond, results mainly from the addition
of the amine to the alkene which has been activated towards
nucleophilic addition through coordination to the pal-
ladium center. Moreover, recent studies from our group re-
vealed that tertiary amines could also be used as nucleo-
philes in a different type of CϪN coupling reaction to af-
ford cationic and neutral heterocyclic compounds[2]. Here
the key step is the formation of an (η3-allyl)PdII intermedi-
ate by a palladium-assisted CϪH activation process. We de-
emed it of great importance to check whether this coupling
reaction could be extended to other nitrogen-containing
systems such as those containing an sp2-hybridised nitrogen
atom. We were especially interested in nitrogen nucleophiles
in pyridinic systems in these heterocyclisation reactions. It
is noteworthy that prior to the work described herein the
intramolecular CϪN coupling of a nitrogen atom at an al-
lylic position was limited mainly to primary or secondary
amines as nitrogen-containing nucleophiles[3]. We can note
that heterocycles obtained in this novel way [i.e. by intra-
molecular addition of a pyridine unit onto a (allyl)Pd de-
rivative] would furnish N-bridgehead heterocycles, many of
rated by a chain of carbon atoms of variable length, in the
ortho position of the pyridine (Scheme 1).
We report herein the reactivity of the pyridine derivatives
1Ϫ5 (they are called o-AlkPy from now on) in the presence
of a palladium(II) complex and base, and we compare this
to the reactions observed previously for tertiary amines. We
will also describe the interactions between the nitrogen
atom and/or the alkene unit and the PdII center, define un-
der which structural conditions an allylic CϪH activation
can take place, and, finally study the depalladation of the
thus formed organopalladium species affording the antici-
pated heterocyclic compounds.
Results
Synthesis of the ortho-Alkenylpyridines
The o-AlkPy ligands 1Ϫ5 are synthesised according to a
known procedure[5]. It is based principally on a CϪC coup-
which display interesting biological properties[4]
.
The substrates we have chosen for this study are ortho- ling reaction between a 2-methylpyridyllithium derivative
alkenylpyridine derivatives bearing a terminal olefin sepa- (prepared in situ) and an alkenyl bromide (Scheme 2).
Eur. J. Inorg. Chem. 1998, 1563Ϫ1571
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J. Chengebroyen, M. Grellier, M. Pfeffer
FULL PAPER
Scheme 2. Synthesis of ortho-alkenylpyridines
In order to check whether it would be possible to gener-
ate an (η3-allyl)PdII complex by deprotonation at the allylic
position, as it was observed in the case of tertiary am-
ines[2a][2b], the chelate adduct 2a was treated with a base.
Indeed, the corresponding (η3-allyl)PdII analogue was
formed. Nevertheless, its poor yield (less than 10%) due to
the formation of a secondary product of the type PdCl2(2)2
(see below), incited us to investigate optimum conditions to
generate the (allyl)Pd complex.
Ligand-PdII-Base Interaction: Formation of (η3-Allyl)PdII
Ligand-PdII Interaction
Complexes
The reaction of the ortho-alkenylpyridines 1Ϫ5 with stoi-
chiometric amounts of PdCl2(MeCN)2 (1:1) leads to the
formation of new coordination chelate complexes (Scheme
3). The stability of these compounds (1a, 2a and 5a) en-
abled their characterisation both in the solid state and in
solution. This is in marked contrast to the corresponding
derivatives obtained previously with ortho-alkenylaniline
or -benzylamine which were only characterised in solution
as they were too unstable to be isolated in the solid state.[2a]
The structure of compound 2a was determined by 1H-
NMR and IR spectroscopy, microanalysis and mass spec-
trometry while compounds 1a and 5a were identified by
The products of the one-pot reaction of the o-AlkPy li-
gands 1Ϫ5 with one equivalent of PdCl2(MeCN)2 and a
base were studied. The reaction conditions and the prod-
ucts formed are indicated in Table 1 below. Several impor-
tant remarks can be made concerning these results. Firstly,
the nature of the final products seems to depend not only
on the number of carbon atoms (n) between the nitrogen
atom and the terminal olefin but also on the nature of R
(R ϭ Me, H). In fact, the formation of an (η3-allyl)pal-
ladium(II) complex, analogous to that obtained in the case
of tertiary amines, is limited to the cases where R ϭ H
and n ϭ 4, 5. In other terms, no allylpalladium complex is
observed for n larger than 5: the same observation was
made in the case of tertiary amines where a different reac-
tivity was noticed for the same length of the carbon chain
separating the terminal olefin and the sp3-hybridised nitro-
gen atom[2a][2b]. Given that the number of carbon atoms
between the nitrogen atom and the allylic fragment in these
two (η3-allyl)PdII complexes (2d and 3d in Table 1) is the
same, we are inclined to believe that in the case of pyridino-
olefins, the formation of the allyl complex is under thermo-
dynamic control. However, the formation, in all cases and
whatever the reaction conditions, of an important quantity
of a secondary product (existing as two isomers except for
5c) consisting of two o-AlkPy ligands and two chlorine
atoms coordinated to the same palladium center, limits the
yield of the allyl complex for n ϭ 4, 5 and R ϭ H. The
latter organopalladium compounds 2d and 3d are indeed
the minor products obtained during this reaction. All at-
tempts (use of different reaction conditions, solvents or
bases) to optimise its yield were unsuccessful: 18% was the
maximum yield obtained for 2d [the PdCl2(2)2 adduct re-
mained the major product of the reaction] when heating a
mixture of 2, 1 equivalent of PdCl2(MeCN)2 and 2.5 equiv-
alents of NaOAc in MeCN at 65°C for 3 h.
1
comparison of their H-NMR spectra with that of 2a and
confirmed by their combustion analyses.
The downfield shift of the ortho proton of the pyridine
ring in the proton-NMR spectrum of 2a indicates that the
nitrogen atom is coordinated to the Pd atom. The coordi-
nation of the olefinic double bond is evidenced by the
shielding of all the protons in the lateral chain. Moreover,
this is confirmed by the fact that when the chelate com-
plexes are treated with one equivalent of PPh3 or NEt3,
used to displace the alkene-Pd interaction, the chemical
shifts of the latter protons are indeed almost identical to
the values observed for the free ligand. In addition, the el-
emental analysis of 2a gave a ratio of 1:2:1 with respect
to palladium, chlorine and the o-AlkPy ligand 2; the mass
spectrum is in agreement with a monomeric species which
was expected due to its solubility. Finally, two absorptions
with mean intensities corresponding to the frequencies of
two PdϪCl vibrations are seen in the far-IR spectrum: the
higher value is assigned to the vibration frequency of the
PdϪCl bond trans to N, and the lower one, to the PdϪCl
bond trans to the olefin[6][7]
.
Scheme 3. Chelate-type interaction between the o-AlkPy ligands
and PdII
It is worth noting that the stability of these PdCl2(li-
gand)2 adducts depends on the value of n. For n < 4 (i.e for
1), this adduct was not stable and was not isolated although
a proton-NMR spectrum of the reaction mixture revealed
unambiguously its presence in solution. When n increases,
a higher yield of the adducts reflects an increase in their
stability. A plausible explanation, based on observations
from L. D. PettitЈs group[5], is the increase in the basicity of
the nitrogen atom as it moves further away from the olefinic
1564
Eur. J. Inorg. Chem. 1998, 1563Ϫ1571

Palladium-Induced Intramolecular Pyridine-Allyl Coupling Reactions
double bond with a negative inductive effect. Consequently,
FULL PAPER
As shown in Scheme 4, ligand 2 is metallated by the pal-
the donor ability of the nitrogen atom, via its lone pair of ladium salt PdCl2(MeCN)2 in the presence of 2 equivalents
electrons, increases. This is confirmed by the chemioselec- of K2CO3 in MeCN to afford the (η3-allyl)PdII complex 2d
tive formation of this adduct in the case n ϭ 6 (compounds and the two isomers 2b and 2c of the adduct PdCl2(2)2 as
4b and 4c). In addition, for longer aliphatic chains (n ϭ 5 the main products, along with some palladium black and
and 6) this adduct is obtained with an isomerisation of the traces of unidentified products. After Celite filtration, 2d
double bond in the lateral carbon chain of the pyridino- (15%) and a mixture of isomers 2b and 2c (30%) were iso-
olefin ligand. The latter reaction is rationalised by a classi- lated by column chromatography on silica gel using ethyl
cal 1,3-hydrogen shift as described by Sen[8] and others[9]
Finally, the simplicity of the 1H- and 13C-NMR spectra
.
acetate as eluant.
The (η3-allyl)PdII complex 2d was structurally character-
(compared to those obtained for a mixture of the two iso- ised by microanalysis and H- and 13C-NMR spectroscopy.
mers) suggests the formation of only one isomer of the The 1H-NMR spectrum shows the presence of the expected
PdCl2(o-AlkPy)2 adduct for ligand 5. An increase in the signals for an η3-allyl fragment: a multiplet at δ ഠ 5.5 corre-
steric bulk around the nitrogen atom resulting from the sponding to Hb, coupled to Ha, Hc and Hd (Scheme 4); the
1
presence of a methyl group in the second ortho position of terminal CH2 group with the characteristic syn (3JHbHc
the pyridine ring would most probably favour the formation 6.68 Hz), anti (3JHbHd ϭ 11.87 Hz) and gem (2JHcHd ϭ 1.1
ϭ
of the anti isomer 5c rather than the syn isomer.
Hz) couplings. The intramolecular coordination of the ni-
Table 1. Ligand-PdII-base interaction
[a]
[b]
Yield of the pure products after a column chromatography on silica gel. Ϫ
Unstable product, not isolated but characterised in
1565
1
solution by H NMR.
Eur. J. Inorg. Chem. 1998, 1563Ϫ1571

J. Chengebroyen, M. Grellier, M. Pfeffer
FULL PAPER
Scheme 4
has the syn configuration. The presence of the methyl group
is confirmed by a doublet integrating for three protons at
3
δ ϭ 1.55 and with a coupling constant JHHc of 6.3 Hz.
Finally, evidence for the intramolecular coordination of the
nitrogen atom comes from the shielding of the ortho proton
(δ ϭ 9.41 compared to 8.47 for the free ligand). The struc-
ture of the syn-(η3-allyl)PdII complex 3d was confimed by
13C-DEPT NMR.
Scheme 5
trogen atom is evidenced by the deshielding of the ortho
proton (δ ϭ 9.4 compared to 8.4 for the free ligand). The
1H-NMR spectrum of 2d indicates the presence of only one
isomer in which the coupling constant between Hb and Ha
is characteristic for two protons in an anti position
(3JHaHb ϭ 11.5 Hz) suggesting that the carbon chain is in
a syn position to Hb.
The PdCl2(2)2 adduct results from the higher affinity of
a palladium(II) center for an sp2-nitrogen atom. This com-
1
The aspect of the H-NMR spectrum of the mixture 3b
1
pound was characterised by H and 13C NMR, elemental
and 3c is also markedly different from that observed for the
mixture of isomers 2b and 2c: the integration of the mul-
tiplets in the olefinic region indicates the presence of fewer
olefinic protons (8 instead of 12). On the other hand, we
noticed the appearence of a new multiplet integrating for
12 protons at δ ϭ 1.7 and corresponding to the methyl
groups. In addition, the 13C-DEPT NMR spectrum shows
a signal for methyl groups, thereby confirming the isomeri-
sation of the olefinic double bond in ligand 3 during the
course of the reaction and prior to the allylic deprotonation
leading to the allyl complex. The same isomerisation pro-
cess was observed in the case of ligand 4 and the analogous
mixture of isomers 4b and 4c was isolated and characterised
(see Table 1).
analysis and IR. The 1H-NMR spectrum shows two distinct
doublets of doublets in a 1:1 ratio at δ ഠ 9. In the presence
of a drop of deuterated pyridine this spectrum remained
unchanged but with a larger excess, the free o-AlkPy ligand
2 and the yellow adduct PdCl2(pyr-D5)2 were formed. All
these observations seem to indicate that the terminal olefin
of the lateral chain is not coordinated and that a simple
adduct is formed by the coordination of o-AlkPy ligand 2
on the palladium(II) center. The combustion analysis is in
agreement with the presence of two chlorine atoms and two
ligands around one atom of palladium. The far-IR spec-
trum of this compound shows only one large and intense
band at 347 cmϪ1: this vibration frequency is characteristic
of a PdϪCl bond trans to a chlorine atom[6][7]. Thus these
data indicate that the PdCl2(2)2 adduct is a mixture of two
isomers, in a 1:1 ratio. For one of these isomers, the two
lateral carbon chains are on the same side of the coordi-
nation plane of the palladium center (syn isomer) and in
Formation of Cationic N-Bridgehead Heterocycles
The (η3-allyl)PdII complexes 2d and 3d are stable in air
the other isomer, they are opposite each other with respect and in solution. However, in the presence of an excess
to this plane (anti isomer). The (η3-allyl)PdII complex 3d (3.5Ϫ4 equivalents) of triphenylphosphane in MeOH or
and the mixture of isomers 3b and 3c (Scheme 5) were iso- MeCN at room temperature, they can be easily demetal-
lated in an analogous way to that described for 2d, 2b and lated[10]. An orange-yellow solution was obtained together
2c. Their structures were determined mainly by 1H and 13C with the precipitation of a pale yellow solid. A proton
NMR. The proton NMR of 3d shows the presence of only NMR of the reaction mixture indicated the presence of only
one compound where the multiplet at δ ϭ 5.5 characteristic one organic compound and the characteristic signals of the
of Hb, the central proton of the allylic unit is no longer phosphane ligands in a Pd0 complex, Pd(PPh3)n. After fil-
observed. Instead a triplet at δ ϭ 5.3 was found, indicating tration through Celite and anion exchange using KPF6 in
that Hb is coupled with Ha and Hc, two magnetically equiv- MeOH, the cationic N-heterocycles 2f and 3f (Scheme 6)
alent protons. This suggests that the (η3-allyl)PdII complex were obtained as pure beige solids. These heterocyclic com-
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Eur. J. Inorg. Chem. 1998, 1563Ϫ1571

Palladium-Induced Intramolecular Pyridine-Allyl Coupling Reactions
FULL PAPER
pounds are indolizinium derivatives incorporating an sp2- has only been observed for two ligands and (ii) that both
hybridised nitrogen atom shared between a pyridine ring compounds do have the same geometry around the (Py-
and a 5-membered ring.
allyl)Pd unit: in both cases a CH2ϪCH2 chain is found be-
tween the pyridine ring and one extremity of the allylic unit.
This is due to the stabilisation of the π-allyl fragment by an
intramolecular coordination of the pyridine, thereby con-
fering an ideal coordination geometry for the palladium
atom in an analogous manner to that observed for a
Scheme 6
Pd(benzylamine-allyl) derivative[2a]
.
Moreover, for ligand 3 a prior CϪH migration is essential
in order to obtain the same type of stabilised (Py-allyl)Pd
compound observed for ligand 2 (see Table 1). However,
this CϪH migration occurs only once since for ligand 4, we
observed only the formation of the bis(ortho-alkenylpyridi-
ne)palladium adduct. This behaviour is in marked contrast
to that of the corresponding ligands bearing an sp3-hybrid-
ised tertiary amine unit[2a][2b], for which the formation of
the (η3-allyl)Pd moiety was always possible (although it
could not be isolated in each case studied) regardless of the
number of carbon atoms between the olefin and the N
atom. We interpret this as a consequence of the strong coor-
dination of the sp2-hybridised nitrogen atom of the pyridine
moiety to the Pd center prior to the CϪH activation at the
allylic position by this metal, whereas for the tertiary amine
alkene derivatives the interaction of the alkene to the pal-
ladium center seems to be the key step of the metallation
process, yielding the (π-allyl)Pd derivatives in a quantitat-
ive way.
The structures of compounds 2f and 3f were deduced
1
from H and 13C NMR, mass spectrometry and combus-
tion analysis. The proton-NMR spectrum of 2f is rather
simple and shows not only that all the protons are different
but also that the protons of the lateral carbon chain res-
onate at lower frequencies compared to those observed for
compound 2d: this general shielding is best explained by the
presence of a positive charge on the nitrogen atom. The
diastereotopicity of the protons of both CH2 groups in 2f
is due to the presence of a stereogenic center α to the nitro-
gen atom. The structure of compound 3f was deduced by
1
comparaison of its H- and 13C-NMR spectra with those
of 2f.
Although the corresponding (η3-allyl)PdII complexes
have been observed for pyridine derivatives, their yields are
low (less than 20%) compared to those for tertiary amine
Discussion
This study was aimed at defining the reactivity of ortho- analogues. These compounds are most likely formed by the
alkenylpyridine ligands with a PdII center in the presence intermediacy of the monomeric chelate adduct where both
of a base. We intended to extend the scope of the unusual the nitrogen atom and the olefin are coordinated to the pal-
reactions that were observed for the related ortho-alkenylan- ladium atom (its presence in solution was unambiguously
ilines or -benzylamines under similar conditions, i.e. the identified by 1H NMR of the reaction mixture at the begin-
palladium-mediated heterocyclisation of these ligands ning of the reaction). However, the CϪH activation process
which occured via the formation of CϪN bonds at the al- takes place only partially since the compounds with two
lylic position[2]
.
ligands per palladium, PdCl2(o-AlkPy)2, are the major
We have noticed one major similarity between tertiary products of the reaction. Nevertheless, once they are
amines and pyridine derivatives concerning the above-men- formed no reverse reaction could be envisaged to transfer
tioned heterocyclisation process: the addition of the nucleo- one species into the other; this result seems to indicate
phile (amine or pyridine) always takes place at an allylic clearly the absence of any type of equilibrium between these
terminal (i.e. after an allylic deprotonation in the presence two PdII compounds. One may anticipate, from our failed
of a base) instead of a direct nucleophilic addition on the attempts to increase the yields of the allylic compounds
activated olefin due to its coordination to a PdII center, as starting from 2a for instance, that the formations of these
observed in the case of primary and secondary amines[1]
.
two classes of compounds are in competition with each
Indeed, the results we have obtained clearly demonstrate other; however, in the absence of any reliable kinetic data
that there is very little similarity between these types of ni- we cannot conclude about this important mechanistic
trogen ligands and the corresponding pyridine derivatives, point.
since in the present work we have mainly observed the for-
It is, however, interesting to note the ease with which the
mation of stable pyridineϪpalladium adducts. This result is allylic compounds can be demetallated to yield quantitat-
not surprising as it is well known that PdII has a much ively heterocyclic compounds with a stable CϪN bond even
larger affinity to a pyridine nitrogen atom as compared to in the presence of Pd0 formed. Indeed, even if some rare
an sp3-hybridised tertiary amine nitrogen atom[11]
.
examples of (allyl)PdII complexes analogous to that ob-
However, in two cases we could observe the formation of served for the pyridino-olefins are known for quinoline de-
some (η3-allyl)Pd-containing complexes by a CϪH acti- rivatives[12], the cyclisation reaction by the addition of an
vation reaction. It is interesting to note that (i) this moiety sp2-nitrogen atom on an allylic fragment has never been
Eur. J. Inorg. Chem. 1998, 1563Ϫ1571
1567

J. Chengebroyen, M. Grellier, M. Pfeffer
FULL PAPER
studied until now. One of the reasons is, most probably, a
Moreover, in the case of substrate 3d, the exocyclisation
reversible reaction implying a CϪN bond rupture, between should be even more favorable owing to the steric effect of
the pyridinium ion formed and the simultaneous obtention the methyl group at the external (Cγ) allylic carbon atom.
of Pd0 during the demetallation reaction. Indeed, allylpyri- Consequently, the nucleophilic attack at this position be-
dinium moities synthesised by other methods are used to comes more difficult[17]
.
generate in the presence of Pd0 an (η3-allyl)PdII complex
and a trisubstituted pyridine (playing the role of a neutral
leaving group) by an oxidative addition of the CϪN bond
on the PdII center[13]. Moreover, another reason which may
justify that hitherto only few studies have been carried out
concerning pyridine-allyl coupling reactions yielding new
CϪN bonds, is the result of the recent study carried out on
the reversible intermolecular addition of a pyridine on an
allylic unit[14]. Thus, this reversibility reflects the instability
of the CϪNϩ bond formed during this study.
The demetallation of the (η3-allyl)PdII compounds is in-
duced by an intramolecular attack of the sp2-hybridised ni-
trogen atom on the allylic fragment and this can occur
either as an endo- or exocyclisation yielding different cyclic
products. In the case of substrate 2d or 3d, only one hetero-
cycle is obtained by the formation of a new CϪN bond
between the sp2-nitrogen and the more substituted carbon
atom Cα to give a 5-membered heterocycle (Scheme 7). We
have, therefore, a remarkably high regioselectivity when tak-
ing into account the two possible electrophilic centers on
the allylic fragment.
Conclusion
The present study shows that even if there is a remarkable
difference in affinity to a palladium(II) center between a
pyridinic sp2-nitrogen and a tertiary amino sp3-nitrogen
atom, it is possible to generate the (η3-allyl)PdII analogue
of the pyridino-olefin derivative. The demetallation of the
latter complex yields, regioselectively and in mild con-
ditions, a stable cationic N-heterocycle by the intramolecu-
lar formation of a CϪN bond between the pyridinic nitro-
gen atom and the allylic C3 unit. Nevertheless, the low yield
of the allylpalladium complex associated with the fact that
it is observed in only a few cases, considerably limits the
scope of this elegant cyclisation reaction for the formation
of cationic N-bridgehead heterocycles. Consequently, new
methods to generate selectively and quantitatively the key
(η3-allyl)PdII intermediate are under investigation.
`
J. C. thanks the Ministere de la Recherche et de l’Enseignement
´
Superieur for partial financial support of this work.
Scheme 7
Experimental Section
General: All the reactions described herein were carried out with-
out any particular precaution unless otherwise stated. All the sol-
vents used were dried beforehand and distilled under nitrogen. The
other commercial starting materials were utilised without further
purification. Filtrations to remove the black deposit of metallic pal-
ladium formed during the depalladation reactions, were performed
using Celite pads. Column chromatography was carried out either
on silica gel (Geduran SI 60; 0.063Ϫ0.200 mm) or on alumina 90
1
(Activity IIϪIII mesh; 0.063Ϫ0.200 mm) from Merck. H- (300.13
or 200.13 MHz), 13C- (75.47 or 50.32 MHz) and 31P-NMR spectra
(81 MHz) were recorded with AC 300 and AC 200 Bruker instru-
ments and externally referenced to TMS. Coupling constants (J)
are given in Hertz. All deuterated solvants were dried with molecu-
According to Baldwin rules governing the formation of
cyclic products[15], both the formation of the 5-membered
heterocycle and that of the 7-membered one are favoured
processes. It is, however, accepted that the formation of 5-
membered rings is more frequent than that of 7-membered
derivatives[16]. An important observation is the fact that in
the case of tertiary amines, for the closely related (π-allyl)Pd
compounds (i.e. those having 3 carbon atoms between the
N atom and the allylic fragment) the endocyclisation pro-
cess was exclusively observed[2a]. This highlights the differ-
ence of the strength of the NϪPd bond in the latter case as
compared to the pyridine compounds: the endocyclisation
could only take place via an intermediate in which the NR2
unit was not coordinated to the palladium atom. On the
other hand, for the pyridine-containing compounds the ex-
ocyclisation could be achieved without dissociation of the
PyϪPd bond by a cis migration of the N atom to the more
substituted allylic carbon atom; however, this assumption
merits a more substantial mechanistic study.
˚
lar sieves (4 A) and stored under nitrogen. Combustion analyses
were performed by the Service Central de Microanalyses du CNRS,
Universite´ Louis Pasteur, Strasbourg, France or by that of Vernai-
son, France. All Mass spectra were performed by the Laboratoire
de Spectroscopie de Masse de lЈUniversite´ Louis Pasteur, Stras-
bourg. IR spectra were recorded with an IRFT Bruker instrument
and the absorption bands are given in cmϪ1
.
Ligands Synthesis: Ligands 1 and 2 were prepared according to
published procedures[5]. Ligands 3, 4 and 5 were synthesised in an
analogous manner. The analytical data for these ligands are listed
below.
Ligand 1: Yellow oil (83%). Ϫ 1H NMR (CDCl3): δ ϭ 8.45Ϫ8.43
(m, 1 H, Ho), 7.48 (td, 1 H, Hm, 3J ϭ 8.4 Hz, 4J ϭ 1.9 Hz), 7.09
(d, 1 H, Hm, 3J ϭ 19.2 Hz), 7.04Ϫ6.97 (m, 1 H, Ar, Hp), 5.86Ϫ5.73
3
(m, 1 H, HCϭC), 5.01Ϫ4.87 (m, 2 H, CϭCH2, Jtrans ϭ 17.1 Hz,
3Jcis ϭ 10.2 Hz), 2.83Ϫ2.78 (m, 2 H, Ar-CH2), 2.47Ϫ2.39 (m, 2 H,
CH2). Ϫ 13C NMR (CDCl3): δ ϭ 161.4, 149.2, 137.7, 136.2, 123.0,
121.0, 115.1 (aromatic and olefinic), 37.7, 33.7 (CH2).
1568
Eur. J. Inorg. Chem. 1998, 1563Ϫ1571

Palladium-Induced Intramolecular Pyridine-Allyl Coupling Reactions
FULL PAPER
Ligand 2: Pale yellow oil (78%). Ϫ The indices allocated to cer-
7.40Ϫ7.26 (m, 2 H, Hp ϩ Hm), 6.91Ϫ6.78 (m, 1 H, CϭCH), 5.85
1
3
3
tain protons are given in Figure 1. Ϫ H-NMR (CDCl3): δ ϭ 8.45
(d, 1 H, CϭCH2, Jcis ϭ 8.2 Hz), 4.41 (d, 1 H, CϭCH2, Jtrans ϭ
14.1 Hz), 3.92 (td, 1 H, CH2, 3J ϭ 12.6 Hz), 3.34Ϫ3.27, 2.80Ϫ2.77,
1.70Ϫ1.54 (3 m, 3 H, CH2). Ϫ C9H11Cl2NPd (310.5): calcd. C
34.79, H 3.54, N 4.51; found C 34.65, H 3.36, N 4.71.
3
(d, 1 H, Ha, JHaHb ϭ 3.4 Hz), 7.52 (m, 1 H, Hc), 7.03 (m, 2 H, Hb
3
3
ϩ Hd), 5.80 (m, 1 H, Hk, JHkHm ϭ 18.8 Hz, JHkHl ϭ 9.3 Hz),
2
4.92 (m, 2 H, Hl ϩ Hm, JHlHm ϭ 1.8 Hz), 2.74 (t, 2 H, Ar-CH2),
2.06 (m, 2 H, CH2ϪCHϭ), 1.80 (m, 2 H, CH2-CH2-CHϭ).
Figure 1. Numbering scheme for the protons of ligand 2
Compound 5a: Orange yellow solid (92%). Ϫ 1H NMR (CDCl3):
3
3
δ ϭ 7.71 (t, 1 H, Ar, J ϭ 7.5 Hz), 7.24 (d, 1 H, Ar, J ϭ 8.3 Hz),
3
7.17 (d, 1 H, Ar, J ϭ 7.7 Hz), 6.55Ϫ6.35 (m, 1 H, CϭCH), 5.65
3
(d, 1 H, CϭCH2, J ϭ 7.1 Hz), 5.18Ϫ5.07 (m, 1 H, CH2), 4.57 (d,
3
1 H, CϭCH2, J ϭ 14.5 Hz), 3.40Ϫ3.32 (m, 1 H, CH2), 3.28 (s, 3
H, CH3), 2.63Ϫ2.43, 2.25Ϫ2.10, 2.05Ϫ1.85, 1.05Ϫ0.82 (4 m, 4 H,
CH2). Ϫ C11.6H16.4Cl2NPd (5a ϩ 0.1 C6H14) (the solvent was de-
1
tected in the H-NMR spectrum) (347.2): calcd. C 40.11, H 4.70,
N 4.03; found C 40.14, H 4.45, N 4.11.
Ligand 3: Orange yellow oil (94%). Ϫ 1H NMR (CDCl3): δ ϭ
8.47 (d, 1 H, Ho, 3J ϭ 4.8 Hz); 7.54 (td, 1 H, Hm, 3J ϭ 7.7, Hz,
Synthesis of the ( η3-Allyl) palladium Complex 2d and of the Mix-
ture 2b ϩ 2c: A suspension containing ligand 2 (1.3 g, 8.8 mmol),
PdCl2(MeCN)2 (2.3 g, 8.8 mmol) and 2 equiv. of NaOAc (1.45 g,
17.6 mmol) in acetonitrile (50 ml) was heated at 65°C for 3 h. A
red solution with a considerable deposit of metallic palladium was
thus obtained. After filtration of the Pd0 so formed through Celite,
the clear solution was concentrated to dryness. The brown oily resi-
due was then extracted with CH2Cl2 (ca. 5 ml). A column chroma-
tography using silica gel and ethyl acetate as eluant allowed the
migration of a first yellow band corresponding to the mixture 2b
ϩ 2c. After solvent evaporation, a yellow solid was obtained (1.25
g; yield 30%). Then a second yellow fraction containing compound
2d was collected (0.412 g; yield 16%).
3
4J ϭ 1.8 Hz), 7.10 (d, 1 H, Hm, J ϭ 7.8 Hz); 7.07Ϫ7.02 (m, 1 H,
Hp), 5.82Ϫ5.71 (m, 1 H, HCϭC), 5.01Ϫ4.88 (m, 2 H, H2CϭC),
2.76 (t, 2 H, Ar-CH2, 3J ϭ 7.7 Hz), 2.11Ϫ2.03, 1.78Ϫ1.67,
1.49Ϫ1.38 (3 m, 6 H, CH2). Ϫ 13C NMR (CDCl3): δ ϭ 162.3,
149.2, 138.8, 136.3, 122.7, 120.9 (aromatic and olefinic), 38.3, 33.6,
29.4, 28.7 (CH2). Ϫ MS; m/z: 162 (Mϩ ϩ H), 120 (Mϩ Ϫ C3H5),
106 (Mϩ Ϫ C4H7), 93 (Mϩ Ϫ C5H8).
Ligand 4: Yellow oil (93%). Ϫ 1H NMR (CDCl3): δ ϭ 8.52Ϫ8.50
3
4
(m, 1 H, Ar, Ho), 7.56 (td, 1 H, Ar, J ϭ 7.7 Hz, J ϭ 1.9 Hz), 7.12
3
(d, 1 H, Ar, J ϭ 7.8 Hz), 7.09Ϫ7.05 (m, 1 H, Ar), 5.86Ϫ5.72 (m,
1 H, HCϭC), 5.01Ϫ4.89 (m, 2 H, CϭCH2), 2.77 (t, 2 H, ArϪCH2,
3J ϭ 7.6 Hz), 2.09Ϫ2.01, 1.78Ϫ1.68, 1.48Ϫ1.32 (3 m, 8 H, CH2).
Ϫ
13C NMR (CDCl3): δ ϭ 162.3, 149.1, 138.9, 136.1, 122.6, 120.8
Compound 2d: Figure 2 indicates the indices attributed to cer-
tain protons.
(aromatic and olefinic CH), 114.2 (olefinic CH2), 38.3, 33.6, 29.7,
28.8, 28.7 (CH2).
Figure 2. Numbering scheme for the protons of ligand 2d
1
Ligand 5: Pale yellow oil (80%). Ϫ H NMR (CDCl3): δ ϭ 7.45
3
(t, 1 H, Ar, J ϭ 7.7 Hz), 6.94Ϫ6.90 (m, 2 H, Ar), 5.87Ϫ5.75 (m,
1 H, HCϭC), 5.04Ϫ4.92 (m, 2 H, CϭCH2), 2.74 (t, 2 H, Ar-CH2,
3J ϭ 7.7), 2.51 (s, 3 H, CH3), 2.14Ϫ2.07, 1.84Ϫ1.74 (2 m, 4 H,
CH2). Ϫ 13C NMR (CDCl3): δ ϭ 161.5, 157.7, 138.5, 136.4, 120.4,
119.5, 114.8 (aromatic and olefinic), 37.9, 33.5, 29.3 (CH2), 24.6
(CH3). Ϫ MS; m/z: 161 (Mϩ), 160 (Mϩ Ϫ H), 120 (Mϩ Ϫ C3H5),
107 (Mϩ Ϫ C4H6).
3
1H NMR (CDCl3): δ ϭ 9.36 (d, 1 H, Ha, JHaH ϭ 5.2 Hz), 7.73,
7.30 (2 m, 3 H, meta and para protons), 5.45 (m, 1 H, Hf, 3JHfHh
11.87 Hz, JHfHg ϭ 6.68 Hz, JHfHe ϭ 11.5 Hz), 3.94 (d, 1 H, Hg),
3.72 (m, 1 H, He, JHeHc ϭ 5.6 Hz), 3.12 (m, 2 H, Hb, JHbHc ϭ
ϭ
Synthesis of the Chelate Adducts
3
3
3
3
Compound 2a: To a suspension of PdCl2(MeCN)2 (0.93 g; 3.6
mmol) in acetonitrile (40 ml) was added dropwise a solution of 6.74 Hz, 3JHbHd ϭ 3.15 Hz), 2.88 (d, 1 H, Hh), 2.05 (m, 1 H, Hc),
ligand 2 (0.525 g; 3.6 mmol). The yellow suspension became gradu- 1.85 (m, 1 H, Hd). Ϫ 13C NMR (CDCl3): δ ϭ 158.2, 152.2, 138.7,
ally homogeneous with increasing amounts of the ligand. The reac-
tion mixture was stirred for 10 min at room temperature. After
removal of the solvent by evaporation, drying, washing with ether
(2 ϫ 40 ml), compound 2a was obtained as a fine, orange-coloured
124.9, 122.9 (aromatic), 111.7, 81.4, 55.9 (allylic), 41.6, 26.4 (CH2).
Ϫ C12H16ClNOPd (2d ϩ 0.5 C4H8O2) (the solvent was detected in
the 1H-NMR spectrum) (332.1): calcd. C 43.37, H 4.82, N 4.22;
found C 43.74, H 4.81, N 4.42.
1
powder (0.985 g; yield 85%). Ϫ H NMR (CDCl3): δ ϭ 8.63 (d, 1
1
Compounds 2b ϩ 2c: H NMR (CDCl3): δ ϭ 9.02 (d, 2 H, Ho,
H, Hortho, 3J ϭ 5.5 Hz), 7.83 (t, 1 H, Hpara, 3J ϭ 7.7 Hz), 7.38Ϫ7.34
(m, 2 H, Hmeta), 6.43Ϫ6.31 (m, 1 H, CH2ϭCH), 5.78 (dd , 1 H,
CH2ϭCH, 3J ϭ 7.7 Hz, 2J ϭ 2.1 Hz), 4.95Ϫ4.83 (m, 1 H,
3J ϭ 5.0 Hz), 8.90 (d, 2 H, Ho, 3J ϭ 4.9 Hz), 7.68 (td, 4 H, Hm, 3J ϭ
7.5 Hz, 4J ϭ 1.6 Hz), 7.30Ϫ7.18 (m, 8 H, Hm ϩ Hp), 6.05Ϫ5.93 (m,
4 H, CϭCH), 5.29Ϫ5.05 (m, 8 H, CϭCH2), 3.96Ϫ3.92 (m, 8 H,
CH2), 2.42Ϫ2.18 (m, 16 H, CH2). Ϫ 13C NMR (CDCl3): δ ϭ 164.0,
152.7, 152.2, 138.2, 138.0, 125.4, 124.5, 122.6 (aromatic carbon
atoms and olefinic CH), 115.7 (olefinic CH2), 39.5, 38.9, 33.8, 33.4,
28.2 (CH2). Ϫ IR (polyethylene pellet): 347 (br, s, νPdϪCl trans to
Cl). Ϫ C20H26Cl2N2Pd (471.7): calcd. C 50.91, H 5.52, N 5.94;
found C 51.62, H 5.52, N 5.63.
3
ArϪCH2), 4.68 (d, 1 H, CH2ϭCH, J ϭ 14.7 Hz), 3.39Ϫ3.32 (m,
1 H, ArϪCH2), 2.61Ϫ2.48, 2.34Ϫ2.16, 2.07Ϫ1.89, 0.95Ϫ0.88 (4 m,
4 H, CH2). Ϫ IR (polyethylene pellet): 341 (br, m, νPdϪCl trans
to N); 308 (br, m, νPdϪCl trans to the olefin). Ϫ MS (FAB); m/z:
328 (Mϩ ϩ 3H), 254 [Mϩ Ϫ 2 Cl)]. Ϫ C10H13Cl2NPd (324.5): calcd.
C 37.01, H 4.04, N 4.32; found C 37.10, H 4.12, N 4.38.
Compounds 1a and 5a were synthesised in the same way as de-
scribed for compound 2a above.
Synthesis of Indolizinium Derivatives 2e and 2f: The reaction of
the allylpalladium complex 2d (220 mg, 0.76 mmol) with 3.5 equiv-
1
Compound 1a: Dark yellow solid (93%). Ϫ H NMR (CDCl3): alents of triphenylphosphane (700 mg, 2.66 mmol) in methanol (20
3
3
δ ϭ 8.93 (d, 1 H, Ho, J ϭ 5.6 Hz), 7.85 (t, 1 H, Hm, J ϭ 7.5 Hz),
ml), at room temperature and under nitrogen, gave an orange solu-
Eur. J. Inorg. Chem. 1998, 1563Ϫ1571
1569

J. Chengebroyen, M. Grellier, M. Pfeffer
FULL PAPER
tion together with a yellow solid that precipitated after only a few
Ar, Hp),, 5.75Ϫ5.40 (m, 8 H, CϭCH), 3.90 (br s, 8 H, H2CϪCϭ),
minutes of reaction. The reaction mixture was allowed to stir for 1 2.60Ϫ2.03 (m, 16 H, CH2), 1.85Ϫ1.58 (m, 12 H, CH3). Ϫ 13C
h. Then after filtration of the fine yellow solid, the filtrate was NMR (CDCl3): δ ϭ 164.3, 160.6, 152.5, 152.1, 138.2, 130.4, 126.3,
concentrated to dryness to give an orange oily residue. Column
chromatography on alumina using a mixture of ether and methanol
126.1, 125.3, 122.4, 121.4 (aromatic and olefinic), 39.6, 39.1, 32.6,
28.9, 26.6, 23.0, 22.5 (CH2), 18.1,14.1 (CH3).
Ϫ
(80:20) as eluant, enabled the migration of a yellow band corre- C22.6H31.2Cl3.2N2Pd (3b, 3c ϩ 0.6 CH2Cl2) (the solvent was de-
1
sponding to the cationic heterocycle 2e (100 mg, crude yield 72%).
tected in the H-NMR spectrum) (550.8): calcd. C 49.27, H 5.67,
Compound 2f (PF6Ϫ as conter anion) was obtained pure as a beige N 5.09; found C 49.18, H 5.35, N 5.28.
solid by treating 2e with KPF6 in methanol (112 mg, yield 51%).
Synthesis of the Indolizinium Derivatives 3e and 3f : Compound
The indices attributed to the different protons in compounds 2e
and 2f are indicated in Figure 3.
3e was prepared by a similar procedure to that described for 2e,
starting from 3d (70 mg; 0.23 mmol) and yielding 3e (36 mg). Com-
pound 3f, with PF6 as counterion instead of ClϪ, was obtained
pure as a pale yellow solid (38 mg; yield 54%), by treating a meth-
anol solution of 3e with KPF6, followed by a column chromatogra-
phy on alumina using the same system of eluant as for 2e.
Ϫ
Figure 3. Numbering scheme for the protons of ligand 2e
3
Compound 3e: 1H NMR (CDCl3): δ ϭ 8.95 (d, 1 H, Ho, J ϭ 6.1
Hz), 8.37 (td, 1 H, Hm, 3J ϭ 6.5 Hz, 4J ϭ 2.0 Hz), 7.99 (d, 1 H,
3
3
Hm, J ϭ 7.9 Hz), 7.93 (t, 1 H, Hp, J ϭ 6.8 Hz), 6.49Ϫ6.37 (m, 1
H, CϭCHMe, 3J ϭ 6.5 Hz), 6.23 (dd, 1 H, NϪCH, J ϭ 8.4, 16.6
3
Hz), 5.59Ϫ5.50 (m,
1 H, HCϭC), 3.87Ϫ3.73, 3.61Ϫ3.51,
3
2.92Ϫ2.82, 2.33Ϫ2.20 (4 m, 4 H, CH2), 1.85 (dd, 3 H, CH3, J ϭ
6.6 Hz, 4J ϭ 1.6 Hz). Ϫ MS (without ClϪ); m/z: 160 (Mϩ), 132
(Mϩ Ϫ C2H4), 106 (Mϩ Ϫ C4H6), 95 (Mϩ Ϫ C5H7).
Compound 2e: 1H NMR (CDCl3): δ ϭ 8.97 (d, 1 H, Ha, 3J ϭ
3
3
5.9 Hz), 8.42 (t, 1 H, Hc, J ϭ 7.7 Hz), 8.09 (d, 1 H, Hd, J ϭ 7.9
Compound 3f: 1H NMR ([D6]acetone): δ ϭ 8.86 (d, 1 H, Ho,
3J ϭ 6.2 Hz), 8.60 (t, 1 H, Hm, 3J ϭ 7.7 Hz), 8.19 (d, 1 H, Hm,
3
3
Hz), 7.93 (t, 1 H, Hb, J ϭ 6.7 Hz), 6.13 (dd, 1 H, Hl, J ϭ 15.2,
7.6 Hz), 6.00Ϫ5.88 (m, 1 H, Hk), 5.68 (d, 1 H, Hi, Jtrans ϭ 16.8
Hz), 5.54 (d, 1 H, Hj, Jcis ϭ 10.0 Hz), 3.70Ϫ3.59, 2.83Ϫ2.77,
3
3J ϭ 7.7 Hz), 8.06 (t, 1 H, Hp, J ϭ 6.6 Hz), 6.37Ϫ6.26 (m, 1 H,
3
3
2.31Ϫ2.24 (4 m, 4 H, He ϩ Hf ϩ Hg ϩ Hh). Ϫ 13C NMR (CDCl3):
δ ϭ 158.1, 145.7, 140.7, 132.8, 126.3, 125.3 (aromatic and olefinic
CH), 124.6 (olefinic CH2), 73.4 (NϪCH), 31.6, 28.6 (CH2). Ϫ MS
(without ClϪ); m/z: 146 (Mϩ), 117 [Mϩ Ϫ (vinyl ϩ 2H)].
CϭCHMe), 5.86Ϫ5.77 (m, 1 H, HCϭC), 5.69 (dd, 1 H, NϪCH,
3J ϭ 8.1, 16.3 Hz), 3.78Ϫ3.61, 2.95Ϫ2.70, 2.51Ϫ2.38 (3 m, 4 H,
3
4
CH2),1.87 (dd, 3 H, CH3, J ϭ 6.6 Hz, J ϭ 1.6 Hz). Ϫ 13C NMR
(CD3OD): δ ϭ 160.5, 146.5, 141.0, 138.9, 127.4, 127.0 (aromatic
and olefinic CH), 126.0 (CH2 olefinic), 75.2 (NϪCH), 32.1, 30.0
(CH2), 18.1 (CH3). Ϫ C11H14F6NP (305.2): calcd. C 43.28, H 4.59,
N 4.59; found: C 43.02, H 4.41, N 4.37.
Compound 2f: 1H NMR ([D6]acetone): δ ϭ 8.89 (d, 1 H, Ha,
3
3
3J ϭ 6.4 Hz), 8.64 (t, 1 H, Hc, J ϭ 8.6 Hz), 8.24 (d, 1 H, Hd, J ϭ
7.8 Hz), 8.11 (t, 1 H, Hb, 3J ϭ 6.8 Hz), 6.28Ϫ6.17 (m, 1 H, Hk),
5.81Ϫ5.68 (m, 1 H, Hl), 5.75 (d, 1 H, Hi, 3Jtrans ϭ 17.0 Hz), 5.69
Synthesis of the Mixture of Isomers 4b and 4c: To a solution
containing PdCl2(MeCN)2 (0.78 g, 3.0 mmol) and ligand 4 (0.528
g, 3.0 mmol) in acetonitrile (40 ml) were added 1.5 equiv. of
NaOAC (0.37 g, 4.5 mmol). The reaction mixture was heated at
65°C overnight. The black deposit of palladium(0) thereby formed
was filtered off using a Celite pad. Then, after evaporation of the
solvent, the brown oily residue obtained was extracted using a mini-
mum of CH2Cl2. Column chromatography on silica gel with ethyl
acetate as eluant allowed the migration of a yellow band containing
the mixture 4b ϩ 4c (0.335 g, yield 42%). Ϫ 1H NMR (CDCl3):
3
(d, 1 H, Hj, Jcis ϭ 10.2 Hz), 3.83Ϫ3.58, 3.05Ϫ2.85, 2.62Ϫ2.42 (3
m, 4 H, He ϩ Hf ϩ Hg ϩ Hh). Ϫ C10H12F6NP (291.2): calcd. C
41.24, H 4.12, N 4.81; found C 40.76, H 4.01, N 4.58.
Synthesis of the ( η3-Allyl) palladium Complex 3d and of the Mix-
ture 3b ϩ 3c: To a mixture containing ligand 3 (0.76 g, 4.7 mmol)
and PdCl2(MeCN)2 (1.22 g, 4.7 mmol) in acetonitrile (50 ml) were
added 2 equiv. of NaOAc (0.77 g, 9.4 mmol). The reaction mixture
was stirred overnight at room temperature. A red solution along
with a deposit of black metallic palladium was obtained. After fil-
tration through Celite and concentration of the filtrate to dryness,
the brown oily residue was extracted with a minimum amount of
CH2Cl2. Column chromatography on silica gel using a mixture of
ether and acetone (85:15) as eluant, allowed the migration of a first
yellow band containing a mixture of isomers 3b ϩ 3c (0.473 g,
yield 34%), followed by the migration of a second yellow fraction
corresponding to the allylpalladium complex 3d (0.142 g, yield
10%).
3
3
δ ϭ 9.00 (d, 2 H, Ho, J ϭ 4.5 Hz), 8.89 (d, 2 H, Ho, J ϭ 5.0 Hz),
7.67 (t, 4 H, Ar, 3J ϭ 3.7 Hz), 7.26 (br t, 4 H, Ar), 7.19 (t, 4 H,
Ar, 3J ϭ 6.5 Hz), 5.40Ϫ5.60 (m, 8 H, HCϭCH), 3.92 (t, 8 H,
H2CϪCϭ, 3J ϭ 7.6 Hz), 2.43Ϫ1.95 (m, 24 H, CH2), 1.80Ϫ1.55
(m, 12 H, CH3). Ϫ 13C NMR (CDCl3): δ ϭ 159.5, 147.7, 147.3,
133.2, 126.2, 126.1, 120.5, 120.1, 117.6 (aromatic and olefinic),
35.2, 34.6, 27.6, 24.9,24.7, 24.0, 23.4 (CH2), 13.1 (CH3). Ϫ
C24H34Cl2N2Pd (527.9): calcd. C 54.61, H 6.45, N 5.31; found C
53.58, H 5.97, N 4.76.
Compound 3d: 1H NMR (CDCl3): δ ϭ 9.41 (d, 1 H, Ar, Ho, 3J ϭ
5.3 Hz), 7.73 (td, 1 H, Ar, 3J ϭ 7.7 Hz, 4J ϭ 1.8 Hz), 7.34Ϫ7.27
Synthesis of Compound 5c: A mixture containing ligand 5 (0.72
g, 4.5 mmol), PdCl2(MeCN)2 (1.17 g, 4.5 mmol) and 1.5 equiv. of
NaOAc (0.55 g, 6.8 mmol) in 50 ml of acetonitrile was heated at
65°C for 3 h. An orange solution containing some black palladium
was observed. After filtration through a Celite pad, the solvent was
evaporated and the brown oily residue formed was extracted using
a minimum of CH2Cl2. Column chromatography on silica gel with
a mixture of CH2Cl2 and hexane (90:10) as eluant allowed the mi-
3
(m, 2 H, Ar), 5.30 (t, 1 H, Hcentral allylic, J ϭ 10.8 Hz), 3.83Ϫ3.65
(m, 1 H, Hallylic), 3.53Ϫ3.43 (m, 1 H, Hallylic), 3.19Ϫ3.01 (m, 2 H,
CH2), 2.13Ϫ1.98 (m, 1 H, CH2), 1.91Ϫ1.71 (m, 1 H, CH2), 1,55
(d, 3 H, CH3, 3J ϭ 6.3 Hz). Ϫ 13C NMR (CDCl3): δ ϭ 158.4, 152.7,
138.5, 124.9, 122.8 (aromatic), 112.6, 76.9, 73.7 (allylic), 41.3, 26.4
(CH2), 17.9 (CH3).
Compounds 3b ϩ 3c: 1H NMR (CDCl3): δ ϭ 9.13Ϫ8.80 (m, 4 gration of a yellow band. After evaporation of the solvents, com-
3
1
H, Ar, Ho), 7.67 (t, 4 H, Ar, Hm, J ϭ 6.4 Hz), 7.40Ϫ7.08 (m, 8 H,
pound 5c was obtained as a beige solid (0.93 g, yield 41%). Ϫ H
1570
Eur. J. Inorg. Chem. 1998, 1563Ϫ1571

Palladium-Induced Intramolecular Pyridine-Allyl Coupling Reactions
FULL PAPER
3
4
Antibiot. Chemother., 7th ed. (engl.) (Eds.: O’Grady, Francis,
Churchill, Livingstone), Edinburgh, UK, 1997, p. 256Ϫ305. Ϫ
E. R. de Oliveira, F. Dumas, J. dЈAngelo, Tetrahedron Lett.
1997, 38, 3723.
NMR (CDCl3): δ ϭ 7.56 (td, 2 H, Ar, J ϭ 7.7 Hz, J ϭ 3.4 Hz),
7.10 (d, 4 H, Ar, 3J ϭ 7.6 Hz), 6.03Ϫ5.90 (m, 2 H, HCϭC),
5.21Ϫ5.06 (m, 4 H, CϭCH2), 4.30Ϫ4.23 (m, 4 H, CH2), 3.63 (s, 6
H, CH3), 2.37Ϫ2.44, 2.21Ϫ2.11 (2 m, 8 H, CH2). Ϫ 13C NMR
([D6]acetone): δ ϭ 165.0, 161.2, 139.8, 139.1, 124.3, 123.1, 115.7
(aromatic and olefinic), 40.1, 34.3, 29.1 (CH2), 27.9 (CH3). Ϫ
C25H37Cl2N2Pd (5c ϩ 0.5 C6H14) (the solvent was detected in the
1H-NMR spectrum) (542.9): calcd. C 55.31, H 6.82, N 5.16; found
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