Synthesis of conjugated (1E,3E)- and (1Z,3Z)-1,4-di(n-pyridyl) (or n-quinolyl)-1,3-butadienes from n-(2′-chloroethenyl)pyridine (or quinoline)

Article abstract of DOI:10.1016/j.tet.2009.01.050

The homocoupling reaction between the conjugated n-(2-chloroethenyl)pyridine; n, 2-, 3- and 4- (or quinoline; n, 2- and 4-) mediated by zero-valent nickel complexes at room temperature affords to the corresponding 1,4-diaryl-1,3-butadiene, always as the 1E,3E stereoisomer. The yield in 1,4-diaryl-1,3-butadiene increases with the nickel catalyst and hence, the active zero-valent nickel catalyst is not regenerated during the homocoupling reaction. The stereospecific synthesis of (1Z,3Z)-1,4-di(4′-pyridyl)-1,3-butadiene stereoisomer was efficiently carried out by partial hydrogenation of the appropriate 1,4-di(4′-pyridyl)-1,3-butadiyne.

Full text of DOI:10.1016/j.tet.2009.01.050

Tetrahedron 65 (2009) 2512–2517
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of conjugated (1E,3E)- and (1Z,3Z)-1,4-di(n-pyridyl)
0
(
or n-quinolyl)-1,3-butadienes from n-(2 -chloroethenyl)pyridine
(
or quinoline)
J.G. Rodr ı´ guez a,*, Cristina D ı´ az-Oliva b
a
Departamento de Qu ´ı mica Org a´ nica, Facultad de Ciencias, Universidad Aut o´ noma, Cantoblanco, 28049-Madrid, Spain
Departamento de Qu ´ı mica F ´ı sica Aplicada, Facultad de Ciencias, Universidad Aut o´ noma, Cantoblanco, 28049-Madrid, Spain
b
a r t i c l e i n f o
a b s t r a c t
Article history:
The homocoupling reaction between the conjugated n-(2-chloroethenyl)pyridine; n, 2-, 3- and 4- (or
quinoline; n, 2- and 4-) mediated by zero-valent nickel complexes at room temperature affords to the
corresponding 1,4-diaryl-1,3-butadiene, always as the 1E,3E stereoisomer. The yield in 1,4-diaryl-1,3-
butadiene increases with the nickel catalyst and hence, the active zero-valent nickel catalyst is not re-
generated during the homocoupling reaction.
Received 4 November 2008
Received in revised form 12 January 2009
Accepted 14 January 2009
Available online 20 January 2009
0
The stereospecific synthesis of (1Z,3Z)-1,4-di(4 -pyridyl)-1,3-butadiene stereoisomer was efficiently
Keywords:
Nickel complexes
0
carried out by partial hydrogenation of the appropriate 1,4-di(4 -pyridyl)-1,3-butadiyne.
Ó 2009 Elsevier Ltd. All rights reserved.
1,4-Diaryl-1,3-butadienes
Homocoupling
Stereospecific hydrogenation
1
. Introduction
presence of the zero-valent nickel complexes, was recently repor-
ted. The active zero-valent nickel species were prepared in situ
from stoichiometric amounts of zinc powder and dichloro bis
11a
The synthesis of the highly conjugated polyene structures as
molecular organic materials show a wide-spread interest because
these exhibit an important stability, semiconductor and optical
properties.1
1
1a
11b
(triphenylphosphine)nickel complex, or catalytic nickel salts.
0
Now, we report the homocoupling of (E)- or (Z)-n-(2 -chloro-
ethenyl)pyridine (or quinoline) containing conjugated electron
withdrawing heterocycle rings, with zero-valent nickel complexes,
to explore the influence of the nitrogen electron lone pair on the
catalyst and the stereochemistry of the reaction.
An elegant and practical synthetic method for 1,4-diphenyl-1,3-
butadiene was the homocoupling of the (E)- or (Z)-b-bromostyrene
with zero-valent nickel complexes giving the (E,E)- or (Z,Z)-1,4-
diphenyl-1,3-butadiene, respectively, while the (E,Z) isomer was
2
always isolated in low yield.
2. Results and discussion
The homocoupling reaction was also investigated with arylsul-
fonates,3 in the presence of the nickel complexes. The Grignard
–5
0
The homocoupling reaction of the n-(2 -chloroethenyl)pyridine
6
,7
reagents in catalytic amounts of nickel complexes, have be used
(or quinoline), having conjugated electron withdrawing heterocy-
cles as the susbtituent on the double bond, in the presence of zero-
valent nickel complexes, was explored to prepare the conjugated
1,4-di(n-pyridyl) (or n-quinolyl)-1,3-butadienes.
8
for the preparation of diaryl or diheteroaryl or polyaryl derivatives.
The homocoupling of organic halides or heteroarylhalides was ef-
ficiently catalysed by electroreductive nickel complexes in organic
9
0
solvent or ionic liquids solvent.
In this way, n-(2 -chloroethenyl)pyridines (1–3) (or quinolines,
The (Z)-3-halopropenoates were homocoupled using catalytic
4 and 5) were prepared by means of the Wittig reaction between
the chloromethylen(triphenyl)phosphorane and n-pyridine (or
quinoline) carboxaldehyde in toluene as yellow oils as a mixture of
the E and Z isomers. For 1, 4 and 5 both isomers were purely isolated
by chromatography and used separately in the homocoupling
reaction.
amounts of nickel chloride and zinc in water with pyridine,
10
affording a mixture of (E) and (Z)-3-hexenedioates.
The homocoupling reaction of the E-, Z- isomers or E/Z mixtures
of
2-chloro-1-(p-N,N-dimethylaminophenyl)ethene,
in
the
The phosphorane reagent was prepared in situ by reaction of
chloromethyl(triphenyl)phosphonium chloride with n-butyl-
*
Corresponding author.
E-mail address: gonzalo.rodriguez@uam.es (J.G. Rodr ı´ guez).
11a,12,13
lithium,
Scheme 1.
0
040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.01.050

J.G. Rodr ´ı guez, C. D ´ı az-Oliva / Tetrahedron 65 (2009) 2512–2517
2513
0
complex but both isomers of 4-(2 -chloroethenyl)pyridine in the
presence of the catalyst decompose at room temperature to give
a water soluble green solid of complicated identification.
nBuLi
ClCH=PPh3
ClCH -PPh3
2
H
0
Complementary, the stable isomer (1Z,3Z)-1,4-di(4 -pyridyl)-
,3-butadiene isomer (8) was stereospecifically obtained in good
yield (96%), by partial catalytic hydrogenation of 1,4-di(4 -pyridyl)-
1,3-butadiyne (9), with partially deactivated palladium catalyst, as
Ar
ClCH=PPh3
O
PPh3
(E/Z)-Ar-CH=CH-Cl
Ar-CHO
1
Cl
H
0
Ar, n-pyridine,1-3;
Ar, n-quinoline, 4, 5
ꢀ
a yellow solid (mp 88–90 C). Compound 9 was prepared by
Scheme 1.
hydrochloric acid elimination of (3) with potassium tert-butoxide
at room temperature, in good yield, Scheme 3.
0
The homocoupling reaction of the n-(2 -chloroethenyl)pyridine
(
or quinoline) derivatives was carried out in the presence of the
Compound 3 was prepared by homocoupling of 4-pyr-
zero-valent nickel complex as catalyst, which was prepared in situ
from dichloro bis(triphenylphosphine) nickel and powder of zinc as
the reducing agent and tetra-n-butylammonium iodide as a phase
transfer component in dry tetrahydrofuran, under argon atmo-
sphere,11 Scheme 2.
idinacetylene catalysed by cuprous chloride in pyridine with ex-
cellent yield. Compound 9 was applied as coordinative agent to
prepare a copper(I) complex forming stable polycatenated molec-
14
ular ladders as a new structural motif in coordination polymers,
Scheme 3.
The experimental results of the homocoupling reaction of n-(2 -
chloroethenyl)pyridines (1–3) mediated by the zero-valent nickel
complex are summarised in Table 1.
0
i.
N
1-2
The electron withdrawing character of quinoline in conjugated
N
0
x-(2 -chloroethenyl)quinolines was also analysed in the homo-
1E,3E 6-7
0
coupling reaction. Thus, 2-(2 -chloroethenyl)quinoline (4a/4b)
was obtained by the Wittig reaction between chloromethylen-
(
triphenyl)phosphorane and 2-quinoline carboxaldehyde, as yellow
4
a
i.
i. Ni[(PPh )] Cl /Zn
N
oil mixture of E/Z (1:1) isomers, in good yield (84%), Scheme 1.
The 2-quinoline carboxaldehyde (or 4-quinoline carboxaldehyde)
was obtained by oxidative treatment of 2-methylquinoline (or 4-
methylquinoline) with freshly sublimated selenium dioxide, as white
4b
N
1
E,3E 10
3
2
2
Scheme 2.
15
(or yellow) crystals in good yield.
0
The homocoupling of (E)-2-(2 -chloroethenyl)pyridine (1a) in
The 2-, 3- and 4-chloroquinolines and their acetylene de-
the presence of the zero-valent nickel complex in 3.3, 1.7 and 1, 1a/
rivatives were obtained and homocoupled to the bis(n-quinolines)
or to the 1,4-di(n-quinolyl)-1,3-butadiynes by other synthetic
0
Ni[(PPh
3
)
2
] catalyst molar ratio, gives always the (1E,3E) 1,4-di(2 -
15
pyridyl)-1,3-butadiene (6) as the unique stereoisomer in 24, 63 and
strategy.
0
9
2% yield, respectively.
The (E)-2-(2 -chloroethenyl)quinoline (4a) isomer was homo-
coupled in the presence of the zero-valent nickel complex under
stoichiometric catalyst at room temperature giving (1E,3E)-1,4-
di(2-quinolyl)-1,3-butadiene (10), as the unique stereoisomer in
85% yield, Scheme 2, Table 2.
In the same way, the homocoupling of the Z isomer (1b) with the
zero-valent nickel complex in 3.3, 1.7 and 1, 1b/Ni[(PPh ) ] catalyst
3 2
molar ratio, gives also the (1E,3E) stereoisomer in 19, 58 and 89%
yield, respectively. Hence, in this case, Z/E isomerisation of 1b
isomer was necessary during the homocoupling reaction.
0
In the same way, the (Z)-2-(2 -chloroethenyl)quinoline (4b)
0
On the other hand, 3-(2 -chloroethenyl)pyridine (2) was
isomer in the presence of the zero-valent nickel complex under
stoichiometric catalyst at room temperature gives (1E,3E)-1,4-di(2-
quinolyl)-1,3-butadiene (10), as the unique stereoisomer in 84%
yield, Table 2. Hence, during the reaction Z/E isomerisation of 4b
takes place.
obtained by the Wittig reaction between the chloromethylen(-
triphenyl)phosphorane and 3-pyridinecarboxaldehyde in toluene
as yellow oil mixture of stereoisomers (2a/2b, 1:1), which was not
possible to separate by chromatographic methods. The homocou-
pling was carried out with the stereoisomeric mixture (2a/2b, 1:1)
in the presence of the zero-valent nickel complex in 3.3, 1.7 and 1,
0
The 4-(2 -chloroethenyl)quinoline (5) was obtained by the
Wittig reaction between the chloromethylen(triphenyl)phosphor-
ane and 4-quinoline carboxaldehyde in hexane as a brown oil,
mixture of isomers (5a/5b, 3:2). Both isomers were isolated by
(
3 2
2a,2b/Ni[(PPh ) ]) catalyst molar ratio, giving exclusively the
0
(
1E,3E)-1,4-di(3 -pyridyl)-1,3-butadiene (7) in 27, 58 and 87%, re-
ꢀ
0
spectively, as a pale yellow solid mp 129–131 C. Hence, during the
homocoupling reaction with the nickel complex a partial Z/E
isomerisation of (Z)-2b was necessary.
chromatography: (E)-4-(2 -chloroethenyl)quinoline (5a) as yellow
ꢀ
0
crystals (mp 45–46 C) and (Z)-4-(2 -chloroethenyl)quinoline (5b),
as colourless oil.
0
In the same way, 4-(2 -chloroethenyl)pyridine (3) was
Both 5a and 5b isomers are stable in solution of hexane under
argon atmosphere but are unstable to the air and to the ambient
light or in contact with the zero-valent nickel complex.
obtained by the Wittig reaction between the chloromethylen
(
triphenyl)phosphorane and 4-pyridinecarboxaldehyde in tolu-
0
ene, as yellow oil mixture (3a/3b, 1:1). The mixture (3a/3b) was
Thus, the homocoupling reaction of (E)-4-(2 -chloro-
used in the homocoupling reaction with the zero-valent nickel
ethenyl)quinoline (5a) in the presence of the zero-valent nickel
N
i.
ii.
iii.
N
3
N
N
N
9
8 (1Z,3Z)
i. KOtBut, THF;
ii. Cu Cl , Py,
iii. H , Pd/BaSO ,
2
4
2
2
Pb(OAc) , Quinoline
2
O
atm., r.t.
2
Scheme 3.

2514
J.G. Rodr ´ı guez, C. D ´ı az-Oliva / Tetrahedron 65 (2009) 2512–2517
Table 1
Homocoupling reaction of x-(2 -chloroethenyl)pyridines with zero-valent nickel
complex in situ production: Ni[(PPh )] Cl
the p–s nickel complex equilibrium, could be responsible of the
0
pathway of the homocoupling and the reason of the 1,3-butadiene
3
2
2
16
stereochemistry, being of minor importance the thermodynamic
ꢀ
17
Subst/Ni, m.r.
.3
.7
n
Compound Isomer
1,3-Butadiene Yield (%) Mp ( C)
stability, Scheme 4.
3
1
2
2
2
2
2
2
3
3
3
4
1a
1a
1a
1b
1b
1b
E
E
E
Z
Z
Z
6 (1E,3E)
6 (1E,3E)
6 (1E,3E)
6 (1E,3E)
6 (1E,3E)
6 (1E,3E)
24
63
92
19
58
89
27
58
87
d
115–117
115–117
115–117
115–117
115–117
115–117
124–126
124–126
124–126
d
On the basis of the electroanalysis of the Ni complex, it was
proposed a mechanism for the homocoupling reaction of aryl
halides through a chain reaction involving several valences of
the nickel complex: Ni(0), Ni(I), Ni(II) and Ni(III) complexes,
1
3
.3
1
.7
18
1
3
Scheme 5.
.3
2a/2b
2a/2b
2a/2b
3a/3b
E/Z, 1:1 7 (1E,3E)
E/Z, 1:1 7 (1E,3E)
E/Z, 1:1 7 (1E,3E)
E/Z, 1:1 Decomposed
The role of the nickel reagents in the activation of the carbon–
halogen bond is commonly interpreted by the involvement of
arylnickel(II) intermediates formed by oxidative addition of the aryl
halide to in situ generated Ni(0) complex. There is general agree-
ment on the biaryl formation by reductive elimination from a dia-
1
.7
1
1
Zero-valent nickel complex: Ni[(PPh
3
)]
2
Cl
2
(n mmol); PPh
3
(4.3 mmol); n-Bu
4
NI
0
(
7.0 mmol); Zn powder (15 mmol); anhydrous THF; 2 -chloroethenylpyridine sub-
18
rylnickel species.
3 2 2
strate (7.0 mmol), molar ratio substrate/Ni[(PPh ) Cl (3.3, 1.7, 1).
0
In general, the homocoupling of 2 -chloroethenylbenzene with
the zero-valent nickel complex affords to a mixture of 1,3-butadi-
1
1a
0
Table 2
ene stereoisomers. In contrast, the homocoupling of 2 -chloro-
ethenylpyridines or quinolines with the zero-valent nickel complex
gives only the 1E,3E stereoisomer. The different stereochemical
behaviour for the homocoupling reaction can be due to the het-
erocyclic nitrogen electron lone pair as donor ligand, which can
interchange the coordination ligands around the nickel complex
responsible of the stereospecificity.
0
Homocoupling reaction of x-(2 -chloroethenyl)quinoline with the zero-valent nickel
complex in situ production: [Ni(PPh
3
)
2
]Cl
2
ꢀ
1,3-Butadiene Yield (%) Mp ( C)
Subst/Ni, m.r.
.0
.0
.0
n
Compound Isomer
1
1
1
2
2
4
4a
4b
E
Z
10 (1E,3E)
10 (1E,3E)
85
84
d
197–198
197–198
d
5a/5b
E/Z, 1:1 Decomposed
Zero-valent nickel complex: Ni[(PPh
3
)
2
]Cl
2
(7.0 mmol); PPh
3
(4.3 mmol); n-Bu
4
NI
0
(
(
7.0 mmol); Zn powder (15 mmol); dry THF; n-(2 -chloroethenyl)quinoline substrate
7.0 mmol).
3. Conclusions
The stereospecific synthesis of (1E,3E)-1,4-dipyridyl (or diqui-
nolyl)-1,3-butadiene can be carried out by the homocoupling re-
action of x-(2 -chloroethenyl)pyridine (or quinoline) mediated by
L
L
0
Cl
Ni
Ni
zero-valent nickel complexes in good yield.
L
L
0
Variable molar ratio of (2 -chloroethenyl)/nickel zero-valent
Cl
H
R
Cl
H
R
H
R
NiL3
complex has been employed and the highest yield in the homo-
coupling product was founded for stoichiometric nickel amounts.
Hence, the nickel catalyst system used was not regenerated along
the reaction.
-
L
H
H
H
π-complex
σ-complex
R, Pyridine
R, Quinoline
E/Z
E
Scheme 4.
4
4
. Experimental
.1. General
complexes, fails because 5a decomposes. In the mixture of reaction
a was partially recovered but the homocoupling product was not
observed.
In the same way, the homocoupling experiments carried out
with (Z)-4-(2 -chloroethenyl)quinoline (5b), in the presence of the
zero-valent nickel complexes, at variable temperature, decomposes
and 5 was recovered as a mixture of the E/Z isomers. The homo-
coupling product was not observed.
The (Z)/(E) isomerisation observed during the homocoupling
reaction of the 2 -chlorovinyl derivatives 1b, 2b, 4b and 5b could be
5
Melting points were determined in open capillaries using
a Reichert hot-stage microscope and are uncorrected. IR spectra of
solids were recorded as KBr pellets and IR spectra of oils were
recorded as thin films on NaCl plates with a Bruker Vector 22
spectrophotometer, and the wave numbers are given in cm . H
and C NMR spectra were recorded at 200 and 50 MHz, re-
spectively, on a Bruker Aspect 200 MHz spectrometer, chemical
0
ꢁ
1 1
13
0
3
shifts are given in d, using CDCl as the solvent and TMS as an in-
ternal reference and constant J values are given in hertz. Mass
spectra were recorded in VG Autospec spectrometer at 70 eV. Ele-
mental analyses were performed with a LECO CHN-900. Yields are
given after silica gel column chromatography separation.
due to the formation of a
decreases the double bond order allowing the rotation of the C–C
bond in the -complex. The formation of a -complex was pro-
p-nickel-double bond complex, which
p
p
posed prior to the oxidative addition to the C–halogen bond by the
nickel complex.16 The volume interactions of the substituents on
0
4
.2. 2-(2 -Chloroethenyl)pyridine (1): general procedure
ArX
ArX
ArNi(II)X2
To a solution of chloromethylen(triphenyl)phosphonium chlo-
ArNi(II)X2
ꢀ
ride (18.7 g, 57 mmol) in dry THF (60 mL), at 0 C was added a so-
lution of BuLi (35.6 mL, 57 mmol, 1.6 M) in hexane, and stirred for
30 min. Then, a solution of 2-pyridincarboxaldehyde (2 g, 19 mmol)
was added, stirring at room temperature for 10 h. After, solvent was
removed at reduced pressure and the residual oil extracted in
hexane (200 mL), dried over magnesium sulfate, filtered and sol-
Ni(0)
Ni(I)X
Ar-Ar
Ni(II)X2
Ar2Ni(III)X
Zn (0)
Zn(II)X2
0
vent removed. The residual oil of 2-(2 -chloroethenyl)-pyridine (1)
Scheme 5.
was a mixture of the E/Z isomers, which was purified by silica gel

J.G. Rodr ´ı guez, C. D ´ı az-Oliva / Tetrahedron 65 (2009) 2512–2517
2515
column chromatography (ethyl acetate/hexane, 2:1) giving 1a (E,
800, 750, 730 (C–H ring).
d
H
8.20 (d, J 8.78 Hz, H-3), 8.13 (d, J
0
.33 g, 12%) and 1b (Z, 1.71 g, 65%) as yellow oils.
6.52 Hz, H-8), 8.08 (d, J 8.78 Hz, H-4), 7.82 (dd, J 6.43, 1.55 Hz, H-5),
.74 (m, H-7), 7.57 (m, H-6), 7.06 (d, J 7.88 Hz, ]CHCl), 6.62 (d, J
7
0
þ
þ
4.2.1. (E)-2-(2 -Chloroethenyl)pyridine (1a)
7.88 Hz, CH]). MS, m/z 189 (M , 22), 191 (M þ2, 7), 154 (100), 128
n
max(film), cmꢁ1, 3070 (]C–H), 1620 (C]C, conj.), 1580 and
(29), 101 (10), 77 (18), 63 (11).
1
560 (C]C and C]N) and 970 (E).
H 3
d (200 MHz; CDCl ) 6.67 (1H, d,
0
J 13.3 Hz, CH]), 7.20 (2H, m, H-3 and H-5), 7.43 (1H, d, J 13.3 Hz,
4.2.6. 4-(2 -Chloroethenyl)quinoline (5a/5b)
]
CHCl), 7.63 (1H, m, H-4) and 8.53 (1H, br s, H-6). MS, m/z 141 (9),
Previously, 4-quinolylcarboxaldehyde was obtained by oxidative
þ
139 (M , 27), 104 (100), 78 (25) and 51 (18).
treatment of 4-methylquinoline with recently sublimed SeO
lowing a reported method, mp 49–51 C.
2
fol-
ꢀ
0
4
.2.2. (Z)-2-(2 -Chloroethenyl)pyridine (1b)
max(film), cmꢁ1, 3055 (]C–H), 1620 (C]C, conj.), 1580 and
560 (C]C and C]N) and 670 (Z). (200 MHz; CDCl ) 6.49 (1H, d,
J 8.3 Hz, CH]), 6.86 (1H, d, J 8.3 Hz, ]CHCl), 7.19 (1H, dd, J 7.9 and
Following the general procedure was obtained a mixture of 5a/
5b (1:1) as a yellow oil, which was isolated by silica gel column
chromatography (ethyl acetate/hexane, 1:1), giving 5a (1.17 g, 40%)
yellow solid (dec), and 5b colourless oil (1.11 g, 38%).
n
1
d
H
3
6
8
8
.0 Hz, H-5), 7.70 (1H, t, J 7.9 Hz, H-4), 8.02 (1H, d, J 7.9 Hz, H-3) and
.62 (1H, d, J 6.0 Hz, H-6). MS, m/z 141 (9), 139 (M , 22), 104 (100),
4 (13), 78 (30) and 51 (27).
þ
4.2.6.1. Compound 5a, E isomer. IR (KBr), 3060 (]C–H), 1620 (C]C,
conj.), 1590 and 1510 (C]C and C]N), and 950 (CH]CHCl, Z), and
8
H
20, 760, 720 (C–H ring). d 8.90 (d, J 4.30 Hz, H-2), 8.15 (dd, J 8.66
0
4
.2.3. 3-(2 -Chloroethenyl)pyridine (2)
and 1.00 Hz, H-8), 8.05 (dd, J 8.69 and 1.6 Hz, H-5), 7.77 (m, H-7),
7.60 (m, H-6), 7.35 (d, J 4.30 Hz, H-3), 6.88 (d, J 12.90 Hz, ]CHCl),
1
Following the general procedure, a mixture of 2a/2b (1:1, by H
NMR) was obtained, as colourless oil (2.38 g, 90%).
050 (]C–H),1610 and 1605 (C]C, conj.),1580 and 1560 (C]C and
ꢁ
1
þ
þ
n
max(film), cm
,
7.55 (d, J 12.90 Hz, CH]). MS, m/z 189 (M , 23), 191 (M þ2, 7), 154
3
(100), 127 (29), 101 (7), 77 (17) and 63 (18).
C]N), 970 (E) and 730 (Z). (200 MHz; CDCl ) 6.29 (1H, d, J 8.2 Hz,
d
H
3
CH], Z), 6.69 (1H, d, J 13.9 Hz, CH], E), 6.74 (1H, d, J 8.2 Hz, ]CHCl,
Z), 6.85 (1H, d, J 13.9 Hz, ]CHCl, E), 7.25 (1H, d, J 8.0 Hz, H-5, E), 7.32
4.2.6.2. Compound 5b, Z isomer. IR (film), 3060 (]C–H), 1620
(C]C, conj.), 1590 and 1510 (C]C and C]N), 730 (]CHCl, Z), and
(
(
1H, dd, J 8.0 and 5.4 Hz, H-5, Z), 7.60 (1H, d, J 8.0 Hz, H-4, E), 8.13
1H, d, J 8.0 Hz, H-4, Z), 8.49 (1H, br s, H-6, E), 8.52 (1H, d, J 5.4 Hz,
H
810, 770, 720 (C–H ring). d 8.85 (d, J 8.51 Hz, H-2), 8.05 (d, J
8.20 Hz, H-8), 7.83 (dd, J 8.20, 1.60 Hz, H-5), 7.65 (m, H-7), 7.55 (d, J
8.51 Hz, H-3), 7.45 (m, H-6), 6.61 (d, J 8.17 Hz, ]CHCl), 7.13 (d, J
H-6, Z), 8.53 (1H, br s, H-2, E) and 8.76 (1H, br ds, H-2, Z). MS, m/z
1
þ
þ
þ
41 (8), 139 (M , 29), 104 (100), 86 (10), 77 (46) and 51 (64).
8.17 Hz, CH]). MS, m/z 189 (M , 28), 191 (M þ2, 9), 154 (100), 127
(
37), 101 (8), 77 (19) and 63 (22).
4
.2.4. 4-(2-Chloroethenyl)pyridine (3)
Following the general procedure, a mixture of 3a/3b (1:1, by H
NMR) was obtained, as colourless oil (2.22 g, 84%). max(film), 3060
]C–H), 1610 (C]C, conj.), 1590 and 1540 (C]C and C]N), 960 (E)
and 720 (Z). (200 MHz; CDCl ) 6.48 (1H, d, J 8.2 Hz, CH], Z), 6.60
1H, d, J 8.2 Hz, ]CHCl, Z), 6.69 (1H, d, J 13.8 Hz, CH], E), 6.77 (1H,
d, J 13.8 Hz, ]CHCl, E), 7.16 (2H, d, J 4.8 Hz, H-3 and H-5, E), 7.52
1
n
4.3. Homocoupling reaction catalysed by dichloro
bis(triphenylphosphine) nickel/Zn system: general procedure
(
d
H
3
(
A suspension of dichloro bis(triphenylphosphine) nickel(II)
(719 mg, 1.1 mmol), tetrabutylammonium iodide (407 mg,
1.1 mmol) and powder of zinc (107 mg, 1.65 mmol) in 5 mL of dry
THF under argon atmosphere, was stirred until the mixture be-
cames dark-red, then it was left to stand for 30 min and a solution
(
2H, d, J 4.6 Hz, H-3 and H-5, Z), 8.56 (2H, d, J 4.8 Hz, H-2 and H-6, E)
þ
and 8.62 (2H, d, J 4.6 Hz, H-2 and H-6, Z). MS, m/z 141 (8), 139 (M ,
2
9), 112 (29), 104 (38), 86 (84), 77 (36), 63 (16) and 51 (100).
0
of the n-(2 -chloroethenyl)pyridine (or quinoline) (1.1 mmol) in dry
0
4
.2.5. 2-(2 -Chloroethenyl)quinoline (4a/4b)
THF (2 mL) was added and stirred at room temperature overnight.
Then, hexane was added to the mixture, filtered and the solvent
removed. The crude product was purified by silica gel column
chromatography.
Previously, 2-quinolylcarboxaldehyde was obtained by oxida-
tive treatment of 2-methylquinoline with recently sublimed SeO
following a reported method, mp 69–71 C.
2
ꢀ
17
To a solution of chloromethylen(triphenyl)phosphonium chlo-
ꢀ
ride (18.7 g, 57 mmol) in dry THF (60 mL), at 0 C was added a so-
4.3.1. Homocoupling of 1a in variable 1a/Ni[(PPh
3
)]
2
Cl
2
molar ratio
0
lution of BuLi (35.6 mL, 1.6 M, 57 mmol) in hexane, and stirred for
Following the general procedure but in variable 2 -chloro-
3
0 min. Then, a solution of 2-quinolylcarboxaldehyde (2.99 g,
3 2 2
ethenyl derivative/Ni[(PPh )] Cl molar ratio of 0.3, 0.6 1.0, was
19 mmol) in hexane (20 mL) was added and stirred at room tem-
always isolated (1E,3E)-1,4-di-(2-pyridyl)-1,3-butadiene (6) as the
perature for 14 h. After, solvent was removed and the residual oil
was purified by silica gel column chromatography (hexane/ethyl
acetate, 1:1) giving the E isomer (4a) as yellow solid (mp 45–46 C)
unique stereoisomer, in 24, 63 and 92% yield, respectively, as yellow
solid, mp 115–117 C.
ꢀ
ꢀ
IR (KBr): 1610 (C]C, conj.), 1575 and 1560 (C]C and C]N), 970
(
1.25 g, 43% yield), and the Z isomer (4b) as colourless oil (1.03 g,
(CH]CH, E).
H
d 8.59 (d, 2H, J 4.9 Hz, H-6), 7.65 (t, 2H, J 7.7 Hz, H-4),
3
5%).
7.34 (d, 2H, J 7.7 Hz, H-3), 7.14 (dd, 2H, J 7.7 and 4.9 Hz, H-5),
0
0
H
A
¼7.49 and H
CH]CH). 155.1 (C-2), 149.5 (C-6), 136.4 (C-4), 134.1 (Py–C]C),
132.3 (C-3), 122.3 and 122.1 (4C, Py–C]C and C-5). MS, m/z 208
x
¼6.84 (AA XX , 4H, JAx¼15.2 Hz, JAx ¼ꢁ0.7 Hz,
0
4.2.5.1. Compound 4a. IR (KBr), 3060 (]C–H), 1610 (C]C, conj.),
d
C
1
590 and 1540 (C]C and C]N), 925 (CH]CHCl, E), 800, 780, 760,
40 (C–H ring). 8.19 (d, J 8.54 Hz, H-8), 8.11 (d, J 8.30 Hz, H-5),
.85 (dd, J 10.31 and 1.24 Hz, H-4), 7.59 (m, H-6), 7.44 (d, J 10.30 Hz,
H-3), 7.42 (d, J 11.45 Hz, ]CHCl), 7.16 (d, J 11.45 Hz, Z, CH]). MS, m/
þ
þ
7
7
d
H
(M , 5), 207 (M ꢁ1, 4), 130 (100), 103 (10), 89 (8), 78 (46), 63 (21)
and 51 (68). Anal. calcd for C14 : C, 80.70; H, 5.85; N, 13.44.
Found: C, 80.45; H, 5.88; N, 13.27%.
12 2
H N
þ
þ
þ
z 189 (M , 20), 191 (M þ2, 8), 154 (100), 128 (M , 29), 101 (16), 77
(
16), 63 (9).
4.3.2. Homocoupling of 1b in variable 1b/Ni[(PPh
Following the general procedure for the homocoupling reaction
of 1b in variable 2-chloroethenyl/Ni[(PPh )] Cl molar ratio of 0.3,
0.6 and 1.0, was always isolated (1E,3E)-1,4-di(2-pyridyl)-1,3-
3 2 2
)] Cl molar ratio
4.2.5.2. Compound 4b. IR (film), 3060 (]C–H), 1610 (C]C, conj.),
3
2
2
1590 and 1540 (C]C and C]N), and 720 (CH]CHCl, Z), and 830,

2516
J.G. Rodr ´ı guez, C. D ´ı az-Oliva / Tetrahedron 65 (2009) 2512–2517
butadiene (6) as the only stereoisomer in 19, 58 and 89% yield,
respectively, as yellow solid, mp 115–117 C.
methanol and purified by silica gel column chromatography (ethyl
ꢀ
0
acetate/hexane, 2:1). (1Z,3Z)-1,4-Di(4 -pyridyl)-1,3-butadiene as
ꢀ
colourless solid mp 88–90 C (0.188 g, 96%).
4.3.3. Homocoupling of (2a/2b, 1:1) in variable (2a/2b)/
Ni[(PPh )] Cl molar ratio
3
2
2
4.3.5.1. Compound 8. IR (KBr), 1590 (C]C), 1580 and 1550 (C]C
0
0
Following the general procedure for the homocoupling of 2 in
and C]N), 700 (]C–H, Z isomer).
d
H
6.51 (AA XX system, J 7.70 Hz,
0
0
0
0
0
0
variable 2 -chloroethenyl (2a/2b, 1:1)/Ni[(PPh
3
)]
2
Cl
2
molar ratio of
2H, H-2 and H-3 ), 6.71 (AA XX system, J 7.70 Hz, 2H, H-1 and H-
0
0
.3, 0.6 and 1.0, was always isolated (1E,3E)-1,4-di-(3-pyridyl)-1,3-
4 ), 7.20 (d, J 5.00 Hz, 4H, H-3 and H-5), 8.58 (d, J 5.00 Hz, 4H, H-2
þ
butadiene (7) as the only stereoisomer in 27, 52 and 87% yield,
respectively, as yellow solid, mp 124–126 C.
and H-6). MS, m/z 208 (34), 207 (M ꢁ1, 100), 130 (24), 104 (3), 77
ꢀ
(13). Anal. calcd for C14
H
12
N
2
: C, 80.70; H, 5.85; N, 13.44. Found: C,
80.54; H, 5.68; N, 13.33%.
4
.3.3.1. Compound 7. IR (KBr): 1615 (C]C, conj.), 1580 and 1560
0
(
C]C and C]N), 960 and 950 (CH]CH, E).
d
H
8.60 (d, 2H, J 2.0 Hz,
4.3.6. Homocoupling of (E)-2-(2 -chloroethenyl)quinoline (4a)
Following the general procedure for the homocoupling of 4a in
4a/Ni stoichiometric molar ratio catalyst was separated (1E,3E)-1,4-
di-(2-quinolyl)-1,3-butadiene (10) as the only stereoisomer in 85%
0
0
H-2 and H-2 ), 8.47 (dd, 2H, J 4.7 and 2.0 Hz, H-6 and H-6 ), 7.60 (td,
0
2
5
H, J 8.0 and 2.0 Hz, H-4 and H-4 ), 7.26 (dd, 2H, J 8.0 and 4.7 Hz, H-
0
0
0
and H-5 ), H
¼ꢁ0.8 Hz, CH]CH).
C]C and C-4),130.1 (Py–C]C),129.7 (C-3),123.2 (C-5). MS, m/z 208
A
¼7.01 and H
x
¼6.68 (AA XX , 4H, JAx¼16.3 Hz,
ꢀ
J
Ax
0
d
C
148.3 (C-2), 148.1 (C-6), 132.2 (4C, Py–
yield, as yellow solid, mp 197–198 C.
þ
þ
(
M , 100), 207 (M ꢁ1, 93), 181 (42), 130 (54), 103 (19), 77 (31), 63
4.3.6.1. Compound 10. IR (KBr): 1610 (C]C, conj.), 1595, 1540 (C]C
(
26) and 51 (34). Anal. calcd for C14 : C, 80.70; H, 5.85; N,13.44.
H
12
N
2
and C]N), 950 (CH]CH, E), 810, 780, 750 and 740.
7.72 Hz, H-8), 8.08 (d, 2H, J 7.65 Hz, H-5), 7.79 (d, 2H, J 7.78 Hz, H-4),
.71 (m, 2H, H-7), 7.65 (d, 2H, J 7.78 Hz, H-3), 7.51 (m,2H, H-6), 7.08–
7.32 (m, 4H). MS, m/z 308 (M , 48), 180 (100), 128 (43), 73 (52), 69
85) and 57 (69). Anal. calcd for C22 : C, 85.68; H, 5.23; N, 9.08.
H
d 8.15 (d, 2H, J
Found: C, 80.39; H, 5.65; N, 13.15%.
7
0
þ
4
.3.4. 1,4-Di(4 -pyridyl)-1,3-diacetylene (9)
(
16 2
H N
4
.3.4.1. 4-Ethynylpyridine. To a solution of 3 (E/Z mixture, 1:1)
Found: C, 85.42; H, 5.09; N, 8.78%.
ꢀ
(
3.2 g, 0.023 mol) in dry THF (48 mL) at 0 C, was added potassium
0
tert-butoxide (6.4 g, 0.057 mol) in THF (64 mL) and stirred at room
temperature for 30 min. The mixture was poured on ice-water and
neutralised with a solution of ammonium chloride (20%) and
extracted with dichloromethane. The organic layer was dried over
magnesium sulfate, filtered and solvent removed and purified by
silica gel column chromatography (ethyl acetate:hexane, 2:1), giv-
4.3.7. Homocoupling of (Z)-2-(2 -chloroethenyl)-quinoline (4b)
Following the general procedure for the homocoupling of 4b/Ni
in stoichiometric molar ratio catalyst of 1.0 was separated (1E,3E)-
1,4-di(2-quinolyl)-1,3-butadiene (10) as the only stereoisomer in
ꢀ
84% yield, as a yellow solid, mp 197–198 C.
ꢀ
0
ing a white solid mp 62–63 C.
4.3.8. Homocoupling of (E)- and (Z)-4-(2 -chloroethenyl)-quinoline
IR (KBr): 3270, 2100 (C^C).
d
H
8.61 (br d, J 6.80 Hz, 2H, H-2 and
(5a and 5b)
H-6), 7.40 (br d, J 6.8 Hz, 2H, H-3 and H-5), 3.40 (s, 1H). MS, m/z 103
Following the general procedure for the homocoupling of 5a (or
5b), in stoichiometric molar ratio catalyst, giving a complex mix-
ture. By silica gel column chromatography (hexane/ethyl acetate,
2:1) was isolated 5a (or 5a/5b) as the main component, but the
homocoupling product was never detected.
þ
(
M , 100), 76 (52), 63 (7).
0
4
.3.4.2. 1,4-Di(4 -pyridyl)-1,3-diacetylene (9). To a solution of cu-
prous chloride (37 mg) in pyridine (2.2 mL) and under oxygen at-
mosphere was added 4-ethynylpyridine (0.73 g, 3.7 mmol) with
ꢀ
stirring at 40–45 C for 1 h. Then, the pyridine was removed at
Acknowledgements
reduced pressure and the residual solid was washed with a solution
of ammonium chloride in water (50 mL, 10%) and extracted with
dichloromethane. The organic layer was newly washed with a sat-
urated aqueous solution of ammonium chloride, dried over mag-
nesium sulfate, filtered and the solvent removed at reduced
We are grateful to the CAM and MEC, projects no. S-0505/PPQ/
0344 and CTQ-2006-15692-C02-01 of Spain, for financial support.
0
pressure giving 1,4-di-(4 -pyridyl)-1,3-diacetylene (9) as yellow
References and notes
solid, which was crystallised from ethanol/water to give a pale
ꢀ
yellow solid mp 199–201 C, (0.69 g, 95%).
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2
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þ
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4
. Baker, R. Chem. Rev. 1973, 73, 487.
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4
.3.5. (1Z,3Z)-1,4-Di(4 pyridyl)-1,3-butadiene (8) by partial
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6
7
8
hydrogenation
In a hydrogenator apparatus were introduced the diacetylene
(9) (0.19 g, 0.95 mmol) and the deactivated palladium on barium
sulfate (0.048 mg, 10% Pd). The deactivated palladium catalyst on
barium sulfate was obtained by treatment with an aqueous solution
of Pb(OAc)
lution of quinoline (0.1 mL) in toluene (5 mL). Hydrogen was in-
troduced at the atmospheric pressure and room temperature. The
mixture was stirred for 4 h and then, the solvent was removed at
reduced pressure giving a residual solid that was extracted with
1
1
ꢀ
2
(0.1 mL, 8%) at 80 C stirring for 5 min and with a so-
1
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1
1
1