A new access to 4 h-quinolizines from 2-vinylpyridine and alkynes promoted by rhodium-N-heterocyclic-carbene catalysts

Article abstract of DOI:10.1002/chem.201300236

Forging the lock that autolocks! Rh-NHC catalysts promote a new access to 4 H-quinolizine species from 2-vinylpyridine and terminal and internal alkynes through C-H activation and C-C coupling reactions (see figure). N-Bridgehead heterocycle formation is favored for internal- over terminal-substituted butadienylpyridine derivatives in a thermal 6π-electrocyclization process. Copyright

Full text of DOI:10.1002/chem.201300236

DOI: 10.1002/chem.201300236
A New Access to 4H-Quinolizines from 2-Vinylpyridine and Alkynes
Promoted by Rhodium–N-Heterocyclic-Carbene Catalysts
Ramꢀn Azpꢁroz, Andrea Di Giuseppe, Ricardo Castarlenas,*
Jesffls J. PØrez-Torrente, and Luis A. Oro*[a]
N-Bridgehead heterocycles are prevalent in many natural
and synthetic biologically active alkaloids.[1] The develop-
ment of efficient synthetic methodologies for the prepara-
tion of these intricate structures has been the focus of in-
tense research,[2] among which transition-metal catalysts
have played a preeminent role.[3] However, derivatives
based on the quinolizine skeleton have received little atten-
tion, probably due to their instability, and are mainly limited
to quinolizidine,[4] quinolizinium salts,[5] or quinolizinone[6]
compounds. Indeed, 4H-quinolizines are very scarce,[7] par-
ticularly the 4-unsubstituted counterparts,[8] and are usually
involved in a tautomeric equilibrium with the corresponding
butadienylpyridine derivatives (Scheme 1).[9] Interestingly,
catalysts bearing NHC ligands give access to the elusive 4H-
quinolizines with total atom economy under mild conditions.
Our research group has recently reported that isolable
ꢀ
mononuclear Rh NHC species can be obtained by an N-
donor-ligand-promoted bridge-cleavage reaction of the cor-
responding dimer.[12c] Similarly, we have now observed that
(h2-coe)}2] (NHC=IPr
the treatment of [{RhACHTUNGERTN(NNUG m-Cl)ACHTUNTRGEG(NNUN NHC)ACHTGUNTRENNUGN
(1), IMes (2); coe=cyclooctene; IPr=1,3-bis-(2,6-diisopro-
pylphenyl)imidazol-2-carbene; IMes=1,3-bis-(2,4,6-trime-
thylphenyl)imidazol-2-carbene) with 2-vinylpyridine afford-
ed [RhClACHTUNGTRNEUNG
(NHC)(k-N,h2-CH2=CHC5H4N)] (NHC=IPr (3),
IMes (4)) in good yields (see the Supporting Information
for synthetic details and NMR data). The chelating coordi-
nation of vinylpyridine is corroborated by an upfield shift
for the olefinic protons (d=3.39–2.13 ppm) and the occur-
rence of JCꢀ coupling for the carbon atoms of the alkenyl
Rh
fragment (d=16–12 Hz) in the H and 13C{1H} NMR spec-
1
tra, respectively.
It has been previously described that rhodium-phosphane
Scheme 1. Tautomerization of 4H-quinolizines.
ꢀ
catalysts efficiently promote the C C coupling between al-
kenylpyridines and olefins,[13] although the coupling with al-
kynes has not been reported to date. Now, we have discov-
ered that the introduction of an NHC ligand in complexes 3
and 4 allow for the straightforward preparation of buta-
we have now observed that the process can be shifted to-
wards the quinolizine tautomer depending on the presence
and position of certain substituents on the dienyl fragment.
However, a straightforward and general method for the
preparation of butadienylpyridines is still an important chal-
lenge for which organometallic catalysts emerge as a crucial
node, as they can potentially achieve this task from 2-vinyl-
dienylpyridines
from
2-vinylpyridine
and
alkynes
(Scheme 2). Notably, the use of 3 and 4 enables terminal al-
kynes to be used in this type of transformation without the
observation of competitive dimerization or polymerization
processes.
ꢀ
pyridine and alkynes through sequential C H activation and
[10]
ꢀ
C C coupling reactions. Particularly, we have been inter-
ested in the design of rhodium catalysts based on N-hetero-
cyclic carbenes (NHCs)[11] for new C C and C X bond-
forming reactions.[12] Now, we have discovered that rhodium
ꢀ
ꢀ
[a] R. Azpꢀroz, Dr. A. Di Giuseppe, Dr. R. Castarlenas,+
Prof. J. J. Pꢁrez-Torrente, Prof. L. A. Oro
Departamento Quꢀmica Inorgꢂnica
Instituto Sꢀntesis Quꢀmica y Catꢂlisis Homogꢁnea
Universidad de Zaragoza-CSIC
ꢀ
ꢀ
Scheme 2. C C coupling reactions mediated by Rh NHC catalysts.
Pl. S. Francisco S/N 50009 Zaragoza (Spain)
E-mail: rcastar@unizar.es
oro@unizar.es
[+] ARAID Foundation Researcher
Catalytic reactions were carried out in an NMR tube in
C6D6 by using a 1:1 ratio of pyridine/alkyne. Preliminary
tests with phenylacetylene under the optimized conditions
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201300236.
3812
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 3812 – 3816

COMMUNICATION
(408C at 5 mol% catalyst loading) showed that 4 was slight-
ly more active than 3 (see Table S1 in the Supporting Infor-
mation). Initially, the formation of (1Z,3E)-2-(4-phenylbuta-
1,3-dien-1-yl)pyridine (Figure 1) was observed, however, un-
expectedly it was accompanied with a new set of resonances
protons, which is fully consistent with the presence of non-
aromatic bicyclic system. The 4H-quinolizine structure was
further confirmed by HSQC and HMBC 1H-13C experi-
ments. Remarkably, the methylene fragment at 4-positon of
the quinolizine skeleton was observed as a singlet at d=
4.38 ppm. Moreover, long-range HSQC 1H-15N correlation
confirms the presence of
a N-bridgehead heterocycle
(Figure 2) with a d
AHCTUNGTRENNUNG
typical range for a trisubstituted amine. In sharp contrast,
the (1E,3E)-butadienylpyridine compound was observed at
d=309.8 ppm.
Figure 1. Monitoring of the reaction between 2-vinylpyridine and phenyl-
acetylene catalyzed by 4 in C6D6 at 408C.
that were unequivocally ascribed to 3-phenyl-4H-quinolizine
(see below). The formation of this product may arise from a
6p-electrocyclization involving the two conjugated double
bonds and one C=N of the pyridine moiety within an unde-
Figure 2. 1H-15N NMR correlation spectrum for a 4H-quinolizine.
tected (1Z,3gem)-butadienylpyridine species.
A similar
transformation has been previously observed for conjugated
imines[14] or oximes[15] but dearomatization of a pyridine
moiety is considerably more challenging.[16] The similar ini-
tial rate for the formation of both organic products points
Catalyst 4 is a versatile precursor for coupling reactions
between 2-vinylpyridine and diverse terminal and internal
alkynes (Table 1). Aromatic terminal alkynes reacted faster
than aliphatic ones and with higher selectivity to 4H-quino-
lizine (Table 1, entries 1–3 vs. 4–6). Isomerization of the in-
ꢀ
out to a lack of regioisomeric preference in the C C cou-
pling process, but the (1Z,3E)-butadienylpyridine product
smoothly isomerizes to produce
the (1E,3E) derivative. A con-
Table 1. Coupling reaction between 2-vinylpyridine and alkynes.[a]
version of 97% was reached
after 4 h with a TOF1/2 value of
35 hꢀ1 calculated at 50% con-
version of 2-vinylpyridine. It is
noticeable that the formation of
Substrate
t
4H-q[b]
Z-E[c]
E-E[c]
Z-g[d]
E-g[d]
vipy[e]
TOF1/2
[hꢀ1
[h]
G
]
1
2
4
1
48
43
3
2
46
48
–
–
–
–
3
7
35
51
4-phenyl-4H-quinolizine
was
not detected. Both butadienyl-
pyridine isomers were isolated
by column chromatography
methods but, unfortunately, the
quinolizine derivative could not
be recovered despite several at-
tempts under different condi-
tions.[14c]
3
4
6
5
36
7
16
37
31
–
8
–
8
1
29
26
45
10
5
9
9
39
–
38
11
3
23
6
7
20
14
7
74
47
2
–
14
–
–
–
2
4
3
16
37
The nature of the new organ-
ic product as 3-phenyl-4H-qui-
nolizine was confirmed by mul-
tinuclear NMR experiments. A
8
9
14
12
51
23
36
69
12
–
–
–
–
1
2
15
3
6[f]
1
striking feature of the H NMR
10
3
45[g]
25[h]
23[h]
–
–
6
18
spectrum is an unusual set of
resonances at higher field (d=
6.6–4.9 ppm) compared with
1
[a] Complex 4 (5 mol%) in C6D6 (0.5 mL) at 408C, [subs]=1m. [b] 4H-Quinolizine; ratio of H NMR integra-
tion. [c] 2-(Buta-1,3-dien-1-yl)pyridine. [d] gem. [e] Unreacted 2-vinylpyridine. [f] E,Z isomer. [g] 4-Methyl.
that corresponding to aromatic [h] 4-Phenyl.
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3813

R. Castarlenas, L. A. Oro et al.
ternal double bond from Z to E occurred also faster for aro-
matic than aliphatic-substituted dienyl derivatives. The pres-
ence of an electron-withdrawing substituent on the phenyl
ring increased the rate whereas selectivity to the N-bridge-
head heterocycle decreased for both, electron-donating or
-withdrawing groups (Table 1, entries 1–3).
The presence of bulky substituents in aliphatic alkynes re-
duced the activity (Table 1, entries 6 and 7). It is noticeable
that the key (1Z,3gem)-butadienylpyridine isomers were de-
tected for aliphatic alkynes, and consequently, the conver-
sion to 3-R-4H-quinolizine is lower, which suggests that the
tautomerization is disfavored in these cases.[17] Monitoring
of the reaction showed that the initially formed Z-gem-buta-
dienylpyridine isomerizes to E-gem derivatives and tauto-
merizes to the 4H-quinolizine compounds (Figure 3). Nota-
Figure 4. Monitoring of the reaction between 2-vinylpyridine and diphe-
nylacetylene catalyzed by 4 in C6D6 at 408C.
2-vinylpyiridine to generate rhodium-alkenyl-hydride spe-
cies is proposed.[19] The subsequent coordination of the
alkyne, migratory insertion and reductive elimination should
generate both (1Z,3E)- or (1Z,3gem)-butadienyl-pyridine
products depending on the regioselectivity. In both cases,
the Z configuration of the internal double bond is kinetical-
ly favored if a concerted insertion mechanism is assumed.
Then, formation of 4H-quinolizine skeletons can be ration-
alized through a metal-mediated or thermal electrocycliza-
tion. To shed light on this point, a solution of pure Z-gem
isomer, (Z)-2-(3-benzylbuta-1,3-dien-1-yl)pyridine, in C6D6
was heated at 608C. Monitoring of the reaction by NMR
spectroscopy evidenced the smooth formation of the 4H-
quinolizine isomer, thus, pointing to a thermally activated
cyclization process. In fact, an equilibrium mixture (butadie-
nylpyridine/heterocycle) of 75:25 was reached after 3 h,
which was corroborated by the exchange peaks observed in
Figure 3. Monitoring of the reaction between 2-vinylpyridine and 3-
phenyl-1-propyne catalyzed by 4 in C6D6 at 408C.
bly, for aliphatic alkynes, the isomerization of 1Z,3E to
1E,3E butadienylpyridines was not detected under catalytic
conditions,[18] whereas internal alkynes reacted smoothly
(Table 1, entries 8–10). The configuration of the conjugated
double bonds of the butadienyl products was confirmed by
1H-NOE NMR experiments (see the Supporting Informa-
tion). In the case of 3-hexyne, the formation of the 1Z,3E
derivative was initially observed with subsequent isomeriza-
tion to 1E,3E and 4H-quinolizine compounds. However, di-
phenylacetylene behaved somewhat different. The initial
rate for the 4H-quinolizine formation was higher but the N-
heterocycle underwent a re-opening to afford the (1Z,3E)-
2-(3,4-diphenylbuta-1,3-dien-1-yl)pyridine derivative with
both phenyl groups disposed
1
the H-NOE NMR spectrum at 808C. It is noticeable that
the formation of the E-gem regioisomer was not observed
indicating that metal catalyst accounts for the Z to E iso-
merization of the internal double bond. A cisoidal configu-
ration of the conjugated double bonds is essential for the
electrocyclic reaction to take place, thus isomerization of
the internal double bond is a handicap to be overcome. A
similar equilibrium mixture was observed after heating the
(1Z,3E)-butadienylpyridine obtained from 3-hexyne, but in
mutually trans (Figure 4). Dis-
symmetric 1-phenyl-1-propyne
gave exclusively 4-methyl-3-
phenyl-4H-quinolizine and 2-
(3-methyl-4-phenylbuta-1,3-
dien-1-yl)pyridine.
Scheme 3 shows a plausible
mechanism for the formation of
the 3-R-4H-quinolizine com-
pounds. Initially, the activation
ꢀ
of a terminal C H bond of the Scheme 3. Plausible mechanism for the formation of 4H-quinolizine derivatives mediated by 4.
3814
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ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 3812 – 3816

A New Access to 4H-Quinolizines
COMMUNICATION
ꢀ
Standard procedure for the catalytic C C coupling between 2-vinylpyri-
this case the equilibrium is further shifted to the quinolizine
compound in 60:40 molar ratio.
dine and alkynes: An NMR tube containing a solution of the catalyst
(0.025 mmol) in of C6D6 (0.5 mL) was treated with 2-vinylpyridine
(0.5 mmol) and the alkyne (0.5 mmol) and heated at 408C. The reaction
course was monitored by NMR and the conversion determined by inte-
gration of the corresponding resonances in the 1H NMR spectra of 2-vi-
nylpyridine and the products.
Theoretical calculations (DFT/m06-2x/kcalmolꢀ1) for the
thermodynamics of the tautomerization process were per-
formed. In full agreement with experimental results, it was
found that 3-phenyl-4H-quinolizine is 1.83 kcalmolꢀ1 more
stable than Z-gem-butadienylpyridine whereas the forma-
tion of 4-phenyl-4H-quinolizine from the (1E,3Z)-butadie-
nylpyridine isomer is disfavored by 2.04 kcalmolꢀ1
(Figure 5). On the other hand, the calculated energies for di-
Acknowledgements
Financial support from the Ministerio de Economꢀa y Competitividad of
Spain Project CTQ2010–15221), the Diputaciꢅn General de Aragꢅn
(E07), the ARAID Foundation under the program “Jꢀvenes Investiga-
dores”, and CONSOLIDER INGENIO-2010, under the Project MULTI-
CAT (CSD2009–00050) are gratefully acknowledged.
ꢀ
ꢀ
Keywords: carbenes · C C coupling · C H activation ·
electrocyclization · quinolizine
[1] a) J. P. Michael, Nat. Prod. Rep. 2008, 25, 139; b) H. F. Ji, L. Shen,
Molecules 2011, 16, 6732; c) R. A. Saporito, M. A. Donelly, T. F.
Spande, H. M. Garraffo, Chemoecology 2012, 22, 159.
Figure 5. Thermodynamic DFT-calculated free energies (DG, kcalmolꢀ1
for the tautomerization of butadienylpyridine$quinolizine.
)
[2] a) S. F. Martin, Pure Appl. Chem. 2009, 81, 195; b) Modern Hetero-
cyclic Chemistry, Vol. 4 (Eds.: J. Alvarez-Builla, J. J. Vaquero, J. Bar-
luenga), Wiley-VCH, Weinheim, 2011; c) H. T. Pham, I. Chataigner,
J.-L. Renaud, Curr Org. Chem. 2012, 16, 1754.
[3] a) J. A. Varela, C. Saa, Chem. Rev. 2003, 103, 3787; b) I. Nakamura,
Y. Yamamoto, Chem. Rev. 2004, 104, 2127; c) D. M. DꢆSouza, T. J. J.
Mꢇller, Chem. Soc. Rev. 2007, 36, 1095; d) S. Perreault, T. Rovis,
Chem. Soc. Rev. 2009, 38, 3149.
[4] a) W. E. Dçring, R. A. N. Weil, J. Am. Chem. Soc. 1947, 69, 2461;
b) K. A. Tehrani, M. D’hooghe, N. De Kimpe, Tetrahedron 2003, 59,
3099; c) C. Tsukano, A. Oimura, I. Enkhtaivan, Y. Takemoto, Org.
Lett. 2012, 14, 1902; d) L. Liu, L. Zhang, Angew. Chem. 2012, 124,
7413; Angew. Chem. Int. Ed. 2012, 51, 7301.
[5] a) B. S. Thyagarajan, Adv. Heterocycl. Chem. 1965, 5, 291; b) C. So-
tiriou-Leventis, A. M. M. Rawashdeh, W. S. Oh, N. Leventis, Org.
Lett. 2002, 4, 4113; c) A. NuÇez, B. Abarca, A. M. Cuadro, J. Alvar-
ez-Builla, J. J. Vaquero, J. Org. Chem. 2009, 74, 4166; d) M. Tian, H.
Ihmels, S. Ye, Org. Biomol. Chem. 2012, 10, 3010.
phenylacetylene were also in agreement with the experimen-
tal results. Although the 4H-quinolizine is 3.24 kcalmolꢀ1
more stable than the (1Z,3Z)-butadienylpyridine isomer,
not detected in the catalytic reaction, tautomerization to the
(1Z,3E) counterpart is also slightly favored (ꢀ0.68 kcal
molꢀ1), thus explaining the smoothly tautomerization ob-
served experimentally (Figure 4).
In conclusion, we have described the outstanding catalytic
ꢀ
ꢀ
performance in C C coupling reactions of new Rh NHC
catalysts leading to the formation of 4H-quinolizine deriva-
tives under mild conditions with total atom economy. We
have shown that the thermal 6p-electrocyclization process
leading to the formation of N-bridgehead heterocycles is fa-
vored for internal- versus terminal-substituted butadienyl-
pyridine derivatives. The design of improved catalysts for se-
lective Z-gem-butadienylpyridine formation and reduced Z
to E isomerization of the internal double bond is ongoing in
our laboratories.
[6] a) V. Boekelheide, C. T. Liu, J. Am. Chem. Soc. 1952, 74, 4920; b) A.
Schwartz, Z. Pꢂl, L. Szabo, K. Simon, I. Hermecz, Z. Mꢁszꢂros, J.
Heterocycl. Chem. 1987, 24, 645; c) M. Hagimori, S. Matsui, N. Miz-
uyama, K. Yokota, J. Nagaoka, Y. Tominaga, Eur. J. Org. Chem.
2009, 5847; d) S. Mochida, N. Umeda, K. Hirano, T. Satoh, M.
Miura, Chem. Lett. 2010, 39, 744.
[7] a) O. Diels, K. Alder, Justus Liebigs Ann. Chem. 1932, 498, 16;
b) R. M. Acheson, G. A. Taylor, J. Chem. Soc. 1960, 1691; c) W. K.
Gibson, D. Leaver, J. Chem. Soc. 1966, 324; d) T. N. Grant, C. L.
Benson, F. G. West, Org. Lett. 2008, 10, 3985.
[8] R. M. Acheson, S. J. Hodgson, R. G. M. Wright, J. Chem. Soc.
Perkin Trans. 1 1976, 1911.
Experimental Section
Synthesis of catalyst 3: A yellow solution of 1 (300 mg, 0.235 mmol) in
toluene (10 mL) was treated with 2-vinylpyridine (50 mL, 0.470 mmol)
and was stirred at room temperature for 1 h. After filtration through
Celite the solvent evaporated to dryness. Addition of hexane caused pre-
cipitation of a yellow solid, which was washed with hexane (3ꢄ4 mL)
and dried in vacuo. Yield: 250 mg (84%). Elemental analysis calcd (%)
for C34H43N3ClRh: C 64.61, H 6.86, N 6.65; found: C 64.92, H 6.89, N
6.62.
[9] a) V. Boekelheide, W. G. Gall, J. Am. Chem. Soc. 1954, 76, 1832;
b) T. Miyadera, E. Ohki, I. Iwai, Chem. Pharm. Bull. 1964, 12, 1344;
c) T. Miyadera, Y. Kishida, Tetrahedron Lett. 1969, 10, 397; d) G. G.
Abbot, D. Leaver, K. C. Mathur, J. Chem. Res. 1978, 224.
[10] a) F. Kakiuchi, S. Murai, Acc. Chem. Res. 2002, 35, 826; b) V. Ri-
tleng, C. Sirling, M. Pfeffer, Chem. Rev. 2002, 102, 1731; c) Y. J.
Park, J. W. Park, C. H. Jun, Acc. Chem. Res. 2008, 41, 222; d) D. A.
Colby, R. G. Bergman, J. A. Ellman, Chem. Rev. 2010, 110, 624;
e) T. W. Lyons, M. S. Sanford, Chem. Rev. 2010, 110, 1147; f) P. B.
Arockiam, C. Bruneau, P. H. Dixneuf, Chem. Rev. 2012, 112, 5879.
[11] a) W. Herrmann, Angew. Chem. 2002, 114, 1342; Angew. Chem. Int.
Ed. 2002, 41, 1290; b) S. Wꢇrtz, F. Glorius, Acc. Chem. Res. 2008,
Synthesis of catalyst 4: The complex was prepared as described for 3
starting from
2 (300 mg, 0.271 mmol) and 2-vinylpyridine (58 mL,
0.542 mmol). Yield: 260 mg (87%). Elemental analysis calcd (%) for
C29H35N3ClRh: C 61.38; H 5.70; N 7.67; found: C 61.05, H 5.80, N 7.26.
Chem. Eur. J. 2013, 19, 3812 – 3816
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3815

R. Castarlenas, L. A. Oro et al.
41, 1523; c) J. M. Praetorius, C. M. Crudden, Dalton Trans. 2008,
4079; d) S. Dꢀez-Gonzꢂlez, N. Marion, S. P. Nolan, Chem. Rev. 2009,
109, 3612.
B. Yue, P. F. Xu, Adv. Synth. Catal. 2010, 352, 2450; f) K. Tanaka, K.
Fukase, S. Katsumura, Synlett 2011, 2115; g) S. Duttwyler, C. Lu,
A. L. Rheingold, R. G. Bergman, J. A. Ellman, J. Am. Chem. Soc.
2012, 134, 4064.
[12] a) M. V. Jimꢁnez, J. J. Pꢁrez-Torrente, V. I. Bartolomꢁ, V. Gierz, F. J.
Lahoz, L. A. Oro, Organometallics 2008, 27, 224; b) A. Di Giuseppe,
R. Castarlenas, J. J. Pꢁrez-Torrente, F. J. Lahoz, V. Polo, L. A. Oro,
Angew. Chem. 2011, 123, 4024; Angew. Chem. Int. Ed. 2011, 50,
3938; c) L. Palacios, X. Miao, A. Di Giuseppe, S. Pascal, C. Cunchil-
los, R. Castarlenas, J. J. Pꢁrez-Torrente, F. J. Lahoz, P. H. Dixneuf,
L. A. Oro, Organometallics 2011, 30, 5208; d) A. Di Giuseppe, R.
Castarlenas, J. J. Pꢁrez-Torrente, M. Crucianelli, V. Polo, R. Sancho,
F. J. Lahoz, L. A. Oro, J. Am. Chem. Soc. 2012, 134, 8171; e) G.
Lꢂzaro, M. Iglesias, F. J. Fernꢂndez-Alvarez, P. J. Sanz-Miguel, J. J.
[15] a) M. L. Meketa, S. M. Weinreb, Y. Nakao, N. Fusetani, J. Org.
Chem. 2007, 72, 4892; b) K. Parthasarathy, M. Jeganmohan, C. H.
Cheng, Org. Lett. 2008, 10, 325; c) K. Kohno, S. Azuma, T. Choshi,
J. Nobuhiro, S. Hibino, Tetrahedron Lett. 2009, 50, 590; d) R. M.
Martin, R. G. Bergman, J. A. Ellman, J. Org. Chem. 2012, 77, 2501.
[16] a) H. Wang, Y. Wang, C. Peng, J. Zhang, Q. Zhu, J. Am. Chem. Soc.
2010, 132, 13217; b) S. P. Roche, J. A. Porco Jr., Angew. Chem. 2011,
123, 4154; Angew. Chem. Int. Ed. 2011, 50, 4068.
[17] Although other metal catalysts promote the formation of (Z,Z)-bu-
tadienylpyridines, the presence of quinolizine tautomers has not
been detected: a) Y. Nakao, K. S. Kanyiva, T. Hiyama, J. Am.
Chem. Soc. 2008, 130, 2448; b) Y. Kuninobu, Y. Fujii, T. Matsuki, Y.
Nishina, K. Takai, Org. Lett. 2009, 11, 2711.
[18] A pure sample of 2-((1Z,3E)-5-phenylpenta-1,3-dien-1-yl)pyridine
in the presence of 5 mol% of 4 gave 33 mol% of the E,E isomer
after 16 h at 808C.
[19] a) G. Jia, D. W. Meek, G. C. Galluci, Organometallics 1990, 9, 2549;
b) R. Castro-Rodrigo, M. A. Esteruelas, S. Fuertes, A. M. Lꢅpez, S.
Mozo, E. OÇate, Organometallics 2009, 28, 5941.
Pꢁrez-Torrente,
cctc.201200309.
L. A.
Oro,
ChemCatChem,
DOI:10.1002/
[13] a) N. Fujii, F. Kakiuchi, N. Chatani, S. Murai, Chem. Lett. 1996, 25,
939; b) Y. G. Lim, J. B. Kang, Y. H. Kim, Chem. Commun. 1996,
585; c) N. Fujii, F. Kakiuchi, A. Yamada, N. Chatani, S. Murai,
Chem. Lett. 1997, 26, 425; d) Y. G. Lim, J.-B. Kang, K. Lee, Y. H.
Kim, Heteroat. Chem. 2002, 13, 346; e) P. Buskens, D. Giunta, W.
Leitner, Inorg. Chim. Acta 2004, 357, 1969.
[14] a) I. Hasan, F. W. Fowler, J. Am. Chem. Soc. 1978, 100, 6696; b) C.
Cao, Y. Li, Y. shi, A. L. Odom, Chem. Commun. 2004, 2002;
c) D. A. Colby, R. G. Bergman, J. A. Ellman, J. Am. Chem. Soc.
2008, 130, 3645; d) T. Kobayashi, K. Takeushi, J. Miwa, H. Tsuchika-
wa, S. Katsumura, Chem. Commun. 2009, 3363; e) H. Wei, Y. Wang,
Received: January 22, 2013
Published online: February 21, 2013
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