Synthesis of 1,4-di(n-pyridyl)buta-1,3-diyne and formation of charge-transfer complexes. X-Ray structure of 1,4-di(3-pyridyl)buta-1,3-diyne

Article abstract of DOI:10.1039/a605468d

Ethynylpyridines have been satisfactorily prepared by two different routes: (a) the Wittig reaction between chloromethylene(triphenyl)phosphine ylide and a pyridinecarbaldehyde, followed by elimination of hydrogen chloride; (b) from the 2-methyl-4-(n-pyridyl)but-3-yn-2-ol intermediate, by elimination of acetone. 1,4-Di(n-pyridyl)buta-1,3-diynes are obtained by oxidative dimerization in good yield. An X-ray structure of the 3-substituted dimer is reported. Mono- and di-methyl salts of the 3-substituted diyne have been obtained and the charge-transfer complexes with tetramethyl-p-phenylenediamine (TMPD) are formed.

Full text of DOI:10.1039/a605468d

View Article Online / Journal Homepage / Table of Contents for this issue
Synthesis of 1,4-di(n-pyridyl)buta-1,3-diyne and formation
of charge-transfer complexes. X-Ray structure of
1,4-di(3-pyridyl)buta-1,3-diyne
J. Gonzalo Rodríguez,*,a Rosa Martín-Villamil,a Felix H. Canob and
Isabel Fonsecab
a
Departamento de Química Orgánica, Universidad Autónoma de Madrid, Cantoblanco,
28049-Madrid, Spain
b Departamento de Cristalografía, C.S.I.C., Serrano 119, 28006-Madrid, Spain
Ethynylpyridines have been satisfactorily prepared by two different routes: (a) the Wittig reaction between
chloromethylene(triphenyl)phosphine ylide and a pyridinecarbaldehyde, followed by elimination of
hydrogen chloride; (b) from the 2-methyl-4-(n-pyridyl)but-3-yn-2-ol intermediate, by elimination
of acetone. 1,4-D i(n-pyridyl)buta-1,3-diynes are obtained by oxidative dimerization in good yield. An
X-ray structure of the 3-substituted dimer is reported. M ono- and di-methyl salts of the 3-substituted
diyne have been obtained and the charge-transfer complexes with tetramethyl-p-phenylenediamine
(TM PD ) are formed.
Table 1 Dehydrochlorination of 1–3 with ButOϪK+ in THF at differ-
ent temperatures
Introduction
The use of molecular organic materials for conductor and non-
linear optics applications is an area of considerable recent
activity. Interest in these materials is due to their inherent syn-
thetic flexibility which permits the ‘design’ of molecular proper-
ties.1 Solid-state polymerization of 1,3-diynes to form crystal-
line conjugated polydiynes has attracted much attention.1,2
Some of the recent interest in poly-1,3-diynes is related to their
large and fast nonlinear optical response, making them good
potential materials in ultrafast optical applications.3 Although
the electronic and optical properties of poly-1,3-diynes are
primarily dominated by the π-conjugated backbone, the sub-
stituent groups markedly influence the topopolymerization
behaviour of the 1,3-diynes and the physical and chemical
properties of the crystalline conjugated poly-1,3-diynes. An
aspect of the substituent effect that has received little attention
is the influence of formally π-conjugated substituents on the
electronic properties of poly-1,3-diynes, because many of them
are unreactive in the solid state,4–6 although they may undergo
liquid-crystalline polymerization to form polymers distinct from
the solid-state polymers. However, preliminary studies show
that 4-amino-4Ј-nitrodiphenyl-1,3-diyne is solid-state reactive.6
The discovery of a one-dimensional metallic state in the ion-
radical solid formed from the π-donor tetrathiafulvalene and
the acceptor tetracyanoquinodimethane has stimulated interest
in the structure–properties relationships of novel donors and
acceptors.7
Chlorovinyl
T/ЊC
Elimination (%)
Substitution (%)
1a
1a
1b
1b
2a + 2b
2a + 2b
3a + 3b
3a + 3b
25
70
50
70
60
70
25
70
48
45
50, E :Z = 1:1
40, E
54
25
40
20
(Z)-2-chlorovinylpyridines 1–3 by dehydrochlorination with
potassium tert-butoxide in tetrahydrofuran (THF) at different
temperatures. In this elimination reaction we observed that the
temperature had an influence on the yield and the reaction
products. Furthermore, the position of the vinyl group on the
pyridine ring determined some of the necessary reaction con-
ditions (Table 1, Scheme 1).
i
CHO
CH=CHCl
N
N
1a,b 2-subst. Z and E
2a,b 3-subst. Z and E
3a,b 4-subst. Z and E
Metallic conductivity and superconductivity are the most
important properties in these organic charge-transfer salts.
Recently, attention has also been directed to the novel magnetic
and optical properties which they can display.
ii
ii
Here we report the synthesis of the 1,4-di(n-pyridyl)buta-1,3-
diynes 12, 13 and 14, and the methylation of the 3-substituted
derivative 13, to give molecules with acceptor characteristics
which allow them to form charge-transfer complexes with
donors.
CH
CH=CHOBut
C
N
N
4 2-subst.
5 3-subst.
6 4-subst.
7a,b 2-subst. Z and E
8
4-subst.
Results and discussion
Scheme 1 Reagents and conditions: i, Ph3P᎐CHCl; ii, ButOϪK+, 25 ЊC
᎐
Synthesis of n-ethynylpyridines
(4–6) or 70 ЊC (7a,b; 8)
(a) By elimination of hydrogen chloride from the chlorovinyl
derivatives. The starting acetylene derivatives 4–6 were prepared
in good yields from a mixture of the corresponding (E)- and
The chlorovinyl derivatives were prepared by the Wittig reac-
tion between chloromethylene(triphenyl)phosphine ylide8 and
J. Chem. Soc., Perkin Trans. 1, 1997
709

View Article Online
Acetylene (%)
Table 2 Synthesis of 1–3 via Wittig reaction
Table 3 Yields of 9–11 and 4–6
Isomer
Z (%)
E (%)
Yield (%)
Bromopyridine
Alcohol (%)
1
2
3
84
50
50
16
50
50
77
90
84
2-subst.
3-subst.
4-subst.
93
98
90
84
55
50
Table 4 Bond distances and angles for 13
the corresponding pyridinecarbaldehyde derivative in THF in
good yield as a mixture of E :Z isomers (Scheme 1, Table 2). In
the case of the 2-substituted derivative the main product is the
Z isomer, because the cis-1,2-oxaphosphetane precursor of this
isomer is more stable. The ylide reacts on the face of the car-
bonyl group to give the oxaphosphetane intermediate with the
dipolar moment of the C᎐Cl bond in the opposite direction to
that of the N᎐C dipole in the pyridine, and this stereodisposi-
tion is the most stable.
(a) Bond distances (Å)
N(1)᎐C(2)
N(1)᎐C(6)
C(2)᎐C(3)
C(3)᎐C(4)
C(4)᎐C(5)
1.338(3)
1.325(3)
1.375(3)
1.371(3)
1.392(3)
C(5)᎐C(6)
C(5)᎐C(7)
C(7)᎐C(8)
C(8)᎐C(8Ј)a
1.394(3)
1.431(3)
1.199(3)
1.371(3)
(b) Bond angles (Њ)
C(2)᎐N(1)᎐C(6)
N(1)᎐C(2)᎐C(3)
C(2)᎐C(3)᎐C(4)
C(3)᎐C(4)᎐C(5)
C(4)᎐C(5)᎐C(7)
117.3(2)
123.1(2)
119.2(2)
119.0(2)
121.2(2)
C(4)᎐C(5)᎐C(6)
C(6)᎐C(5)᎐C(7)
N(1)᎐C(6)᎐C(5)
C(5)᎐C(7)᎐C(8)
C(7)᎐C(8)᎐C(8Ј)a
117.4(2)
121.4(2)
123.9(2)
178.1(2)
179.7(2)
(b) From the n-halogenopyridines by insertion of the acetylene
group catalysed by palladium. The low yield in the hydrogen
chloride elimination step prompted us to carry out an altern-
ative synthesis of the acetylene derivatives of pyridine using the
coupling reaction between the bromopyridine and 2-methyl-
but-3-yn-2-ol;9 the reaction is catalysed by palladium and
the 2-methyl-4-(n-pyridyl)but-3-yn-2-ol derivatives 9–11 were
obtained in excellent yields. Finally, the elimination of acetone
gave the acetylene derivatives in moderate yield (Scheme 2,
Table 3).
a
C(8Ј) is related to C(8) by the symmetry operation (1 Ϫ x, Ϫ1 Ϫ y,
2 Ϫ z).
scheme. A table of fractional atomic coordinates has been
deposited as supplementary material,† and in Table 4 are listed
(a) the bond distances and (b) the bond angles. The molecule has
a symmetry centre which coincides with a crystallographic one.
The distances N(1)᎐C(2) and N(1)᎐C(6) of 1.338(3) and
1.325(3) Å respectively are similar to those found in pyridine.
All distances and angles are within the expected values (Table
4). The pyridine ring is planar, C(7) and C(8) deviating by
0.031(2) and 0.086(2) Å above this plane.
Bond distances of the buta-1,3-diyne chain show normal
values,11 with a C(7)᎐C(8) triple bond distance of 1.199(3) Å.
This chain is practically linear with a C(7)᎐C(8)᎐C(8Ј) angle of
179.7(2)Њ.
CH3
i
Br
C
C
C
OH
N
N
CH3
9
2-subst.
10 3-subst.
11 4-subst.
ii
The crystal packs with the molecules in parallel columns (see
Fig. 2) along the c-axis which defines the distance between the
centroids of consecutive rings as being 3.87 Å, forming with the
c-axis an angle of 10Њ. It can be seen in Fig. 2 that along the a-
axis there are zones of neighbouring intermolecular rings and
C
CH
N
4–6
Scheme 2 Reagents and conditions: i, 2-methylbut-3-yn-2-ol, Cl2Pd-
(PPh3)2, Cu2I2, HNEt2; ii, NaOH, reflux
᎐
᎐
zones of intramolecular ᎐C᎐C᎐C᎐C᎐ linear chains, producing a
᎐
᎐
so called ‘segregation’, the overall least-squares planes through
each molecule in the cell are parallel and within each column
a stack is produced. Along the b-axis there are also chains
of molecules in the so called ‘edge-to-edge’ mode with parallel
molecules within a column but forming an angle of almost 90Њ
between molecules of two neighbouring columns.
Synthesis of 1,4-di(n-pyridyl)buta-1,3-diynes 12–14
The title compounds were synthesized in good yield by oxi-
dative dimerization 10 of the corresponding acetylene derivative
with oxygen in pyridine in the presence of copper(I) iodide at
40 ЊC as solids which are stable to sunlight (Scheme 3).
In general, in the reactive crystals of buta-1,3-diyne com-
pounds, the molecules are packed in a ladder-like fashion such
that the ends of one triple-bond system approach an adjacent
triple-bond system to a distance d <4 Å, and the inclination
angle formed with the translation axis is about 45Њ.12
C
CH
C
C
C
C
N
N
N
4 2-subst.
5 3-subst.
6 4-subst.
12 2-subst.
13 3-subst.
14 4-subst.
Charge-transfer complexes
The π-electronic defect of the pyridine rings and the π-
extended conjugation to the diyne chain in 1,4-di(3-pyridyl)-
buta-1,3-diyne 13 allowed it to take part in charge-transfer
complexation with N,N,NЈ,NЈ-tetramethyl-p-phenylenediamine
(TMPD) as donor. However, the 1,4-di(n-pyridyl)buta-1,3-
diyne derivative does not form charge-transfer complexes with
Scheme 3 Reagents: Cu2CI2, O2, pyridine
A single crystal of the 1,4-di(3-pyridyl)buta-1,3-diyne 13 was
used for X-ray crystallographic analysis. The crystal was stable
to Cu-Kα X-radiation and no topopolymerization to the
monocrystalline poly-1,3-diyne was observed.
† Supplementary material: Tables of fractional atomic coordinates and
thermal parameters, and full bond lengths and angles, have been
deposited at the Cambridge Crystallographic Data Centre (CCDC). See
Instructions for Authors, J. Chem. Soc., Perkin Trans. 1, 1997, Issue
1. Any request to the CCDC for this material should quote the full
literature citation and the reference number 207/78.
Crystal structure analysis
Compound 13 consists of a buta-1,3-diyne chain with 1,4-
substitution at position 3 in both pyridine rings.
Fig. 1 shows a view of the molecule with the atom numbering
710
J. Chem. Soc., Perkin Trans. 1, 1997

View Article Online
Fig. 1 View of molecule 13 with the atom numbering scheme
some acceptors or donors, so we carried out methylation of the
pyridine rings to increase the acceptor character of these com-
pounds (Scheme 4).
Fig. 2 Packing of the molecular crystal unit cells viewed down the b-
axis
C
C
C
C
N
N
13
H3C
CH3
CH3
N
C
N
H3C
C
C
C
N
N+I–
CH3
C
C
C
C
C
C
N
N+I–
15
CH3
+
H3C
CH3
CH3
N
C
N
C
C
H3C
C
–I+N
N+I–
CH3
16
H3C
C
C
–I+N
N+I–
CH3
Scheme 4 Reagent: MeI
H3C
The mono- and di-methylated salts of the meta diyne derivative
were isolated pure and used to prepare charge-transfer com-
plexes with the donor molecule TMPD. Thus, slow evaporation
of an equimolar mixture of the mono- or di-salt and TMPD in
hot acetonitrile gave in both cases a metallic bright solid (black
or green) (Fig. 3).
UV-Visible spectroscopy of the molecular complex of the
monomethylated salt 15 and TMPD shows three charge-
transfer bands, at 543, 565 and 615 nm. In the case of the
molecular complex of the dimethylated salt 16 and TMPD the
UV-visible spectrum also shows three charge-transfer bands, at
594, 617 and 642 nm. The IR spectra showed some differences
between the complexes with TMPD and the free salts, such that
Fig. 3
Preparation of ethynylpyridines by elimination of hydrogen
chloride from the chlorovinyl derivatives
2-(2-Chlorovinyl)pyridine 1. To a suspension of chloromethyl-
(triphenyl)phosphonium chloride (18.7 g, 57 mmol) in dry THF
(60 cm3) was slowly added a solution of butyllithium (1.6  in
hexane; 35.6 cm3, 57 mmol) under argon at Ϫ10 ЊC. The solu-
tion acquired a red colour and after being stirred for 30 min was
treated with pyridine-2-carbaldehyde (2 g, 19 mmol). The mix-
ture was stirred at room temperature for 10 h and then the
solvent was removed to give a brown oil. Chromatography on
silica gel with hexane–ethyl acetate afforded (Z)-2-(2-chloro-
vinyl)pyridine, νmax(film)/cmϪ1 3055 (᎐C᎐H), 1620 (C᎐C, conj.),
the intensity of the absorption for the C᎐C conjugated bonds in
᎐
the complexes is lower than that in the free salts.
᎐
᎐
1580 and 1560 (C᎐C and C᎐N) and 670 (Z); δ (200 MHz;
᎐
᎐
H
CDCl ) 6.49 (1 H, d, J 8.3, CH᎐CHCl), 6.86 (1 H, d, J 8.3,
᎐
3
Experimental
CH᎐CHCl), 7.19 (1 H, dd, J 7.9 and 6.0, 5-H), 7.70 (1 H, t, J
᎐
Mps were determined using a Reichert stage microscope and
are uncorrected. IR Spectra were recorded using a Perkin-Elmer
681 spectrophotometer. NMR Spectra were recorded at 200
MHz using a Bruker WM-200-SY spectrometer; chemical shifts
are given in δ units, using SiMe4 as internal reference; J values
are given in Hz. UV–Visible spectra were recorded using a
Perkin-Elmer Lambda 6 spectrophotometer. Mass spectra were
recorded using a Hewlett-Packard SP85 spectrometer.
7.9, 4-H), 8.02 (1 H, d, J 7.9, 3-H) and 8.62 (1 H, d, J 6.0, 6-H);
m/z 141 (9%), 139 (M+, 22), 104 (100), 84 (13), 78 (30) and 51
(27); and (E)-2-(2-chlorovinyl)pyridine, νmax(film)/cmϪ1 3070
(᎐C᎐H), 1620 (C᎐C, conj.), 1580 and 1560 (C᎐C and C᎐N) and
᎐
᎐
᎐
᎐
970 (E); δ (200 MHz; CDCl ) 6.67 (1 H, d, J 13.3, CH᎐CHCl),
᎐
H
3
7.20 (2 H, m, 3- and 5-H), 7.43 (1 H, d, J 13.3, CH᎐CHCl), 7.63
᎐
(1 H, m, 4-H) and 8.53 (1 H, br s, 6-H); m/z 141 (9%), 139 (M+,
27), 104 (100), 78 (25) and 51 (18).
J. Chem. Soc., Perkin Trans. 1, 1997
711

View Article Online
᎐
3280 (᎐C᎐H) and 2120 (C᎐C); δ (200 MHz; CDCl ) 3.30 (1 H,
᎐ ᎐
H 3
3-(2-Chlorovinyl)pyridine 2. The same procedure was fol-
lowed to prepare the 3-substituted derivative, but with pyridine-
3-carbaldehyde. After purification by chromatography on
silica gel the chlorovinyl derivative 2 was obtained as an oily
mixture of E : Z isomers (1:1) (2.38 g, 90%); νmax(film)/cmϪ1
3050 (᎐C᎐H), 1610 and 1605 (C᎐C, conj.), 1580 and 1560
᎐
s, C᎐CH), 7.25 (1 H, ddd, J 7.8, 5.0 and 0.9, 5-H), 7.70 (1 H, dt,
J 7.8 and 2.0, 4-H), 8.56 (1 H, dd, J 5.0 and 2.0, 6-H) and 8.70
(1 H, dd, J 2.0 and 0.9, 2-H); δC(200 MHz; CDCl3) 80.0
᎐
᎐
᎐
᎐
(Py᎐C᎐C), 80.6 (Py᎐C᎐C), 118.7 (C-3), 122.3 (C-5), 138.3
᎐
(C-4), 148.3 (C-6) and 151.9 (C-2); m/z 103 (M+, 100%), 76 (38)
and 50 (30).
᎐
᎐
(C᎐C and C᎐N), 970 (E) and 730 (Z); δ (200 MHz; CDCl )
᎐
᎐
H
3
6.29 (1 H, d, J 8.2, CH᎐CHCl, Z), 6.69 (1 H, d, J 13.9,
4-Ethynylpyridine 6. Following the same procedure described
to prepare 2-ethynylpyridine from the (Z )-chlorovinyl isomer,
4-ethynylpyridine was obtained (40%) as a solid from the
᎐
CH᎐CHCl, E), 6.74 (1 H, d, J 8.2, CH᎐CHCl, Z), 6.85 (1 H,
᎐
᎐
d, J 13.9, CH᎐CHCl, E), 7.25 (1 H, d, J 8.0, 5-H, E), 7.32 (1
᎐
H, dd, J 8.0 and 5.4, 5-H, Z), 7.60 (1 H, d, J 8.0, 4-H, E),
8.13 (1 H, d, J 8.0, 4-H, Z), 8.49 (1 H, br s, 6-H, E), 8.52 (1
H, d, J 5.4, 6-H, Z), 8.53 (1 H, br s, 2-H, E) and 8.76 (1 H,
br s, 2-H, Z); m/z 141 (8%), 139 (M+, 29), 104 (100), 86 (10),
77 (46) and 51 (64).
4-(chlorovinyl)isomer, mp 63–65 ЊC; νmax(film)/cmϪ1 3270
᎐
(᎐C᎐H) and 2100 (C᎐C); δ (200 MHz; CDCl ) 3.40 (1 H, s,
᎐
᎐
᎐
H
3
C᎐CH), 7.35 (2 H, d, J 6.8, 3- and 5-H) and 8.60 (2 H, d, J 6.8,
2- and 6-H); δ (200 MHz; CDCl ) 80.6 (Py᎐C᎐C), 81.8
᎐
᎐
᎐
C
3
᎐
(Py᎐C᎐C), 129.9 (C-4), 125.7 (C-3 and -5) and 149.4 (C-2 and
᎐
4-(2-Chlorovinyl)pyridine 3. Following the same procedure
we obtained the chlorovinyl derivative 3, from pyridine-4-
carbaldehyde, as an oily mixture of E : Z isomers (1:1) (2.22 g,
84%); νmax(film)/cmϪ1 3060 (᎐C᎐H), 1610 (C᎐C, conj.), 1590
-6); m/z 103 (M+, 100%), 76 (52) and 50 (41).
Synthesis of ethynylpyridines by insertion of the acetylene group
catalysed by palladium
᎐
᎐
and 1540 (C᎐C and C᎐N), 960 (E) and 720 (Z); δ (200 MHz;
2-Methyl-4-(2-pyridyl)but-3-yn-2-ol 9. Bis(triphenylphos-
phine)palladium(II) dichloride (220 mg, 0.3 mmol) and cop-
per(I) iodide (32 mg, 0.2 mmol) were added successively to a
solution of 2-bromopyridine (5 g, 31.6 mmol) and 2-methylbut-
3-yn-2-ol (3.62 ml, 37.3 mmol) in diethylamine (freshly distilled;
25 cm3) under argon at 0 ЊC. The mixture was stirred for 15 h at
room temperature and then the diethylamine was removed
under reduced pressure. The crude mixture was washed with
water and extracted with dichloromethane; the extract was
dried with magnesium sulfate and after filtration the solvent
was removed to give a brown solid. Chromatography on silica
gel with hexane–ethyl acetate as eluent yielded 2-methyl-4-(2-
pyridyl)but-3-yn-2-ol 9 (4.76 g, 93%) as a yellow solid, mp 60–
᎐
᎐
H
CDCl ) 6.48 (1 H, d, J 8.2, CH᎐CHCl, Z), 6.60 (1 H, d, J 8.2,
᎐
3
CH᎐CHCl, Z), 6.69 (1 H, d, J 13.8, CH᎐CHCl, E), 6.77 (1
᎐
᎐
H, d, J 13.8, CH᎐CHCl, E), 7.16 (2 H, d, J 4.8, 3- and 5-H,
᎐
E), 7.52 (2 H, d, J 4.6, 3- and 5-H, Z), 8.56 (2 H, d, J 4.8, 2-
and 6-H, E) and 8.62 (2 H, d, J 4.6, 2- and 6-H, Z); m/z 141
(8%), 139 (M+, 29), 112 (29), 104 (38), 86 (84), 77 (36), 63
(16) and 51 (100).
2-Ethynylpyridine 4. From the (Z)-2-(2-chlorovinyl)pyridine
isomer 1a.—To a solution of the (Z)-chlorovinyl derivative 1a
(3 g, 21 mmol) in dry THF (30 cm3) was slowly added potas-
sium tert-butoxide (6 g, 54 mmol) under argon at 0 ЊC. The
mixture was stirred for 45 min at room temperature. Then the
solution was poured onto ice–water (150 cm3) and made alka-
line (pH 8) with saturated aq. ammonium chloride. The mixture
was extracted with dichloromethane; the extract was dried with
magnesium sulfate and after filtration the solvent was removed
to give a brown oil. Chromatography on silica gel with hexane–
ethyl acetate (1:2) as eluent yielded the acetylene derivative 4
(1.04 g, 48%) as an orange oil, bp 91–92 ЊC/15 mmHg (lit.,9 85–
62 ЊC (lit.,9 61–63 ЊC); νmax(film)/cmϪ1 3300 (O᎐H), 2980 (C᎐H),
᎐
2230 (C᎐C), 1585 (C᎐C, conj.), 1380 and 1360 (CH ), 1170
᎐
᎐
3
(C᎐O), 970 (Py) and 780 (Py᎐H, 2-subst.); δH (200 MHz; CDCl3)
1.70 (6 H, s, CH3 × 2), 5.29 (1 H, s, OH), 7.20 (1 H, dd, J 6.7
and 5.0, 5-H), 7.39 (1 H, d, J3,4 6.7, 3-H), 7.62 (1 H, td, J4,3 = J4,5
6.7 and J4,6 0.8, 4-H) and 8.59 (1 H, br s, 6-H); δC(200 MHz;
᎐
CDCl3) 30.9 (CH3), 64.5 (C᎐OH), 80.6 (Py᎐C᎐C), 94.9
᎐
86 ЊC/12 mmHg); νmax(film)/cmϪ1 3260 (᎐C᎐H) and 2114 (C᎐C);
(Py᎐C᎐C), 122.5 (C-5), 126.7 (C-3), 136.0 (C-4), 142.6 (C-2)
᎐
᎐
᎐
᎐
᎐
᎐
δ (200 MHz; CDCl ) 3.25 (1 H, s, C᎐CH), 7.21 (1 H, dd, J 7.7
and 149.2 (C-6).
᎐
H
3
and 5.1, 5-H), 7.40 (1 H, d, J 7.7, 3-H), 7.60 (1 H, t, J 7.7, 4-H)
and 8.54 (1 H, d, J 5.1, 6-H); δC(200 MHz; CDCl3) 77.0
2-Methyl-4-(3-pyridyl)but-3-yn-2-ol 10. Following the same
procedure the 3-substituted derivative 10 was obtained (5 g,
98%) as a yellow solid, from 3-bromopyridine, mp 52–54 ЊC;
᎐
᎐
᎐
(Py᎐C᎐C), 82.5 (Py᎐C᎐C), 123.1 (C-5), 127.1 (C-3), 135.8
᎐
(C-4), 148.4 (C-2) and 149.5 (C-6); m/z 103 (M+, 100%), 76
(46) and 50 (36).
νmax(film)/cmϪ1 3300 (O᎐H), 2980 (C᎐H), 2240 (C᎐C), 1590
᎐
᎐
(C᎐C, conj.), 1380 and 1360 (CH ), 1170 (C᎐O), 970 (Py) and
᎐
3
From the (E)-2-(2-chlorovinyl)pyridine isomer 1b.—To a
solution of the (E)-chlorovinyl derivative 1b (1 g, 7.2 mmol)
in dry THF (15 cm3) was slowly added potassium tert-butoxide
(2 g, 18 mmol), under argon at 0 ЊC. The mixture was stirred for
90 min at 50 ЊC. Then the solution was poured onto ice–water
(60 cm3) and made alkaline (pH 8) with saturated aq. ammo-
nium chloride. The mixture was extracted with dichlorometh-
ane; the extract was dried with magnesium sulfate and after
filtration the solvent was removed to give a brown oil. Chrom-
atography on silica gel with hexane–ethyl acetate (1:2) as elu-
ent yielded the acetylene derivative 4 (0.33 g, 45%) as an orange
oil.
810 and 705 (Py᎐H, 3-subst.); δH (200 MHz; CDCl3), 1.58 (6 H,
s, CH3 × 2), 5.78 (1 H, s, OH), 7.15 (1 H, dd, J5,4 8.0, J5,6 6.4,
5-H), 7.09 (1 H, d, J4,5 8.0, 4-H), 8.38 (1 H, s, 6-H) and 8.60
(1 H, s, 2-H); δC(200 MHz; CDCl3) 31.1 (CH3), 64.3 (C᎐OH),
᎐
᎐
77.6 (Py᎐C᎐C), 98.6 (Py᎐C᎐C), 120.2 (C-3), 122.9 (C-5), 138.7
᎐
᎐
(C-4), 147.4 (C-6) and 151.3 (C-2).
2-Methyl-4-(4-pyridyl)but-3-yn-2-ol 11. The preparation of
the 4-substituted derivative 11 was carried out, following the
same procedure, from 4-bromopyridine hydrochloride. Com-
pound 11 was obtained (3.72 g, 90%) as a yellow solid, mp 96–
98 ЊC; νmax(film)/cmϪ1 3350–3040 (O᎐H), 2980 (C᎐H), 2230
᎐
(C᎐C), 1600 (C᎐C, conj.), 1370 and 1360 (CH ), 1170 (C᎐O),
᎐
᎐
3
3-Ethynylpyridine 5. To a solution of the (Z,E)-chlorovinyl
derivative 2 (3 g, 21 mmol) in dry THF (30 cm3) was slowly
added potassium tert-butoxide (6 g, 54 mmol) under argon at
0 ЊC. The mixture was stirred for 60 min at 60 ЊC. Then the
solution was allowed to cool and was poured onto ice–water
(150 cm3) and made alkaline (pH 8) with saturated aq. ammo-
nium chloride. The mixture was extracted with dichloro-
methane; the extract was dried with magnesium sulfate and
after filtration the solvent was removed to give a brown oil.
Chromatography on silica gel with hexane–ethyl acetate (1:2)
as eluent yielded the acetylene derivative 5 (1.17 g, 54%) as a
yellow solid, mp 35–37 ЊC (lit.,13 39–40 ЊC); νmax(film)/cmϪ1
970 (Py) and 840 (Py᎐H, 4-subst.); δH (200 MHz; CDCl3) 1.62
(6 H, s, CH3 × 2), 3.10 (1 H, s, OH), 7.29 (2 H, d, J 8.1, 3- and
5-H) and 8.59 (2 H, s, 2- and 6-H); δC(200 MHz; CDCl3) 31.0
᎐
᎐
(CH ), 64.5 (C᎐OH), 78.6 (Py᎐C᎐C), 100 (Py᎐C᎐C), 125.6 (C-3
᎐
᎐
3
and -5) and 148.8 (C-2 and -6).
General procedure to prepare the ethynylpyridines from the
2-methyl-4-(n-pyridyl)but-3-yn-2-ols
A solution of the alkynol (5 g, 31 mmol) in dry toluene (30 cm3)
was heated under reflux with pulverized sodium hydroxide (0.90
g) for 2 h. Then, the solution was decanted and the solvent was
evaporated under reduced pressure to give a brown solid.
712
J. Chem. Soc., Perkin Trans. 1, 1997

View Article Online
Chromatography on silica gel with hexane–ethyl acetate (1:2)
yielded the ethynyl derivative 2-Ethynylpyridine (84%) as an
orange oil, bp 90–92 ЊC/15 mmHg; 3-ethynylpyridine (55%)
as a yellow solid, mp 37–39 ЊC and 4-ethynylpyridine (50%) as a
solid, mp 63–65 ЊC.
1,4-Di(2-pyridyl)buta-1,3-diyne 12
To a suspension of copper(I) chloride (57 mg, 0.58 mmol)
and N,N,NЈ,NЈ-tetramethylethylenediamine (TMEDA) (0.11
cm3, 0.75 mmol) in 1,2-dimethoxyethane (DME) (4 cm3) was
added a solution of 2-ethynylpyridine 4 (0.3 g, 2.9 mmol) in
DME (1 cm3), previously heated for 10 min at 35 ЊC, while
oxygen was bubbled in. After 30 min the mixture changed in
colour from green to brown and 15 min later the solvent was
removed to give a brown solid, chromatography of which on
silica gel with hexane–ethyl acetate (2:3) as eluent yielded the
diacetylene derivative 12 (150 mg, 52%) as a solid, mp 120–
Oxidative dimerization of ethynylpyridines. General procedure
Oxygen was bubbled into a solution of copper(I) chloride (0.54
g, 2.73 mmol) in pyridine (12 cm3) warmed to 40 ЊC, after
which the acetylene derivative (0.78 g, 7.57 mmol) was added.
The mixture was stirred for 3 h, after which it was cooled and
concentrated by removal of the pyridine by distillation. The
crude mixture was washed with ammonium hydroxide until the
blue colour disappeared, after which it was extracted with
dichloromethane. The extract was dried (MgSO4), filtered and
evaporated to give a yellow solid, chromatography of which on
silica gel with hexane–ethyl acetate (1 : 2) as eluent yielded the
diyne derivative. 3-Substituted product 13 (49%) was a yellow
122 ЊC (lit.,19 122–123 ЊC); νmax(KBr)/cmϪ1 1580 and 1560 (C᎐C,
᎐
conj.), 990 (Py), 780 and 735 (Py᎐H, 2-subst.); δH (200 MHz,
CDCl3) 7.24 (2 H, ddd, J 7.6, 4.8 and 1.1, 5-H), 7.47 (2 H, d, J
7.7, 3-H), 7.63 (2 H, td, J 7.7 and 1.7, 4-H) and 8.55 (2 H, d, J
᎐
᎐
4.8, 6-H); δ (200 MHz; CDCl ) 72.9 (Py᎐C᎐C), 80.7 (Py᎐C᎐C),
᎐
᎐
C
3
123.6 (C-5), 128.2 (C-3), 136.0 (C-4), 141.5 (C-2) and 150.2
(C-6); m/z 204 (M+, 100%), 177 (14), 151 (14), 124 (5), 102 (6)
and 78 (10); λmax(CH2Cl2)/nm 238 (ε/dm3 molϪ1 cmϪ1 23 600),
294 (18 400), 309 (24 000) and 330 (20 800).
solid, mp 145–146 ЊC; νmax(KBr)/cmϪ1 1550 (C᎐C, conj.), 955
᎐
(Py), 800 and 700 (Py᎐H, 3-subst.); δH (200 MHz; CDCl3)
7.30 (2 H, dd, J 7.9 and 5.0, 5-H), 7.82 (2 H, dt, J 7.9 and
1.7, 4-H), 8.61 (2 H, br s, 6-H) and 8.78 (2 H, br s, 2-H);
Methylation of the 1,4-di(3-pyridyl)buta-1,3-diyne 13
᎐
δ (200 MHz; CDCl ) 78.9 (C᎐C), 118.5 (C-3), 122.7 (C-5),
To a solution of the diyne derivative (100 mg, 0.49 mmol) in
ethanol (25 cm3) was added iodomethane (0.12 cm3, 1.96
mmol). The mixture was stirred for 20 h at 50 ЊC. A yellow solid
precipitated from the solution and was filtered off and identi-
fied as the dimethylated derivative 16 (92 mg, 38%), mp 190 ЊC
(decomp.). Then, the mixture was allowed to cool and an
orange solid precipitated out, which was filtered off and identi-
fied as the monomethylated derivative 15 (72 mg, 42%), mp
166 ЊC (decomp.).
᎐
C
3
139.1 (C-4), 149.2 (C-6) and 152.9 (C-2); m/z 204 (M+, 100%),
177 (11), 151 (23) and 124 (8); λmax(CH2Cl2)/nm 229 (ε/dm3
molϪ1 cmϪ1 30 000), 244 (29 000), 292 (22 000), 319 (30 000)
and 331 (26 000).
4-Substituted product 14 (54%) was a brown solid, mp 198–
201 ЊC; νmax(Nujol)/cmϪ1 1580 (C᎐C, conj.), 980 (Py) and 810
᎐
(Py᎐H, 4-subst.); δH (200 MHz; CDCl3) 7.41 (4 H, d, J 7.2, 3-
and 5-H) and 8.67 (4 H, br s, 2- and 6-H); δC(200 MHz;
CDCl ) 76.9 (Py᎐C᎐C), 79.9 (Py᎐C᎐C), 125.7 (C-3 and -5),
Dimethylated product 16 had νmax(KBr)/cmϪ1 1620 and 1500
᎐
᎐
᎐
᎐
3
128.9 (C-4) and 149.6 (C-2 and -6); m/z 204 (M+, 100%), 177
(C᎐C and C᎐N, conj.), 1290 (N᎐CH ), 1150 (Py+–CH ), 810 and
᎐
᎐
3
3
(13), 151 (14) and 124 (6).
665 (Py᎐H, 3-subst.); δH [200 MHz; (CD3)2SO] 4.37 (6 H, s,
CH3 × 2), 8.23 (2 H, t, 5-H), 8.91 (2 H, d, 4-H), 9.13 (2 H, d,
X-Ray crystallographic analysis of 1,4-di(3-pyridyl)buta-1,3-
diyne 13
6-H) and 9.49 (2 H, s, 2-H); δC(200 MHz; CDCl3) 48.4 (CH3),
᎐
77.2 and 77.6 (Py᎐C᎐C), 120.1 (C-3), 127.7 (C-5), 146.4 (C-4),
᎐
Yellow, transparent, plate-like crystals of 1,4-di(3-pyridyl)buta-
1,3-diyne 13 were grown by slow evaporation from an aceto-
nitrile solution. A crystal of dimensions 0.29 × 0.27 × 0.18
mm3 was selected for X-ray diffraction analysis. Accurate cell
dimensions were determined by least-squares analysis of setting
angles of 40 reflections (15 < 2θ < 84Њ) using graphite-mono-
chromated Cu-Kα radiation (λ = 1.5418 Å) automatically
located and centred on a four-circle Philips PW1100 diffrac-
tometer. C14H8N2, M = 204.23, monoclinic, a = 22.104(3), b =
6.017(1), c = 3.873(1) Å, β = 91.48(1)Њ, V = 514.92(7) Å3, Z = 2,
space group P21/n, Dc = 1.317(3) g cmϪ3, F(000) = 212, µ = 6.253
147.9 (C-6) and 149.3 (C-2); m/z (FAB+) 234 (M+, 25%) and
219 (52); λmax(CH2Cl2)/nm 237 (ε/dm3 molϪ1 cmϪ1 31 430), 290
(18 500), 308 (20 000), 330 (18 570), 345 (13 710), 354 (12 000)
and 360 (11 430).
Monomethylated product 15 had νmax(KBr)/cmϪ1 1620, 1580
and 1500 (C᎐C and C᎐N, conj.), 1280 (N᎐CH ), 1160
᎐
᎐
3
(Py+᎐CH3), 830, 800, 700 and 675 (Py᎐H, 3-subst.); δH [200
MHz; (CD3)2SO] 4.31 (3 H, s, CH3), 7.50 (1 H, m, 5-H), 8.20 (2
H, m, 5-H in the methylated ring and 4-H), 8.70 (2 H, m, 2- and
6-H), 8.88 (1 H, m, 4-H in the methylated ring), 9.05 (1 H, d,
6-H in the methylated ring) and 9.42 (1 H, br s, 2-H in the
cmϪ1
.
methylated ring); δC(200 MHz; CDCl3) 48.4 (CH3), 77.2 and
᎐
Data collection. Two standard reflections were measured
every 90 min to ascertain crystal stability; no significant vari-
ation was observed. The intensities were corrected for Lorentz
and polarization effects. No corrections were made for
absorption.
77.6 (Py᎐C᎐C), 120.1 (C-3), 127.7 (C-5), 146.4 (C-4), 147.9
᎐
(C-6) and 149.3 (C-2); m/z (FAB+) 219 (M+, 100%) and 205 (13);
λmax(CH2Cl2)/nm 237 (ε/dm3 molϪ1 cmϪ1 40 250), 290 (17 750),
308 (22 500), 330 (24 000) and 345 (12 500).
For the intensity measurement, reflections were surveyed
in the range 2 < θ < 65Њ; from 975 independent reflections
measured, 778 were considered as observed, satisfying the
criterion I < 2σ(I) in the range h Ϫ27/27, k 0/8, l 0/5, and were
used in the subsequent calculations. The structure was solved
by direct methods using SIR92,14 and refined by aniso-
tropic full-matrix least-squares.15 The H-atoms were located
on a difference map and refined isotropically. After several
cycles of mixed refinement (89 refined parameters), con-
vergence was reached at R = 0.057 and Rw = 0.069, with a
weighting scheme16 to prevent trends in 〈w∆2F〉 vs. 〈|Fo|〉 and
〈sinθ/λ〉.
Charge-transfer complex of 1-(N-methylpyridinium-3-yl)-4-(3-
pyridyl)buta-1,3-diyne iodide 15 with TMPD
A hot solution of TMPD (24 mg, 0.14 mmol) in acetonitrile
(10 cm3) was added to a nearly boiling solution of the mono-
methylated buta-1,3-diyne derivative 15 (50 mg, 0.14 mmol) in
100 cm3 of acetonitrile. The resulting dark violet solution was
allowed to cool and then to evaporate slowly to yield a black
solid with metallic lustre; νmax(Nujol)/cmϪ1 1610, 1580 and 1510
(C᎐C and C᎐N, conj.), 1160 (Py+᎐CH ), 950 (Py), 820, 810, 800,
᎐
᎐
3
720, 690 and 665 (Py᎐H, 3-subst.); λmax(CH2Cl2)/nm 238, 309,
330, 350, 543, 565 and 615.
The atomic scattering factors and the anomalous dispersion
corrections were taken from the literature.17 Atomic coordin-
ates, bond distances and angles were calculated using the
PARST program.18
Charge-transfer complex of 1,4-bis(N-methylpyridinium-3-yl)-
buta-1,3-diyne diiodide 16 with TMPD
The same procedure was followed to form the charge-transfer
complex of the dimethylated buta-1,3-diyne derivative 16.
J. Chem. Soc., Perkin Trans. 1, 1997
713

View Article Online
8 G. Köbrig, H. Trapp, K. Flory and W. Drischel, Chem. Ber., 1966,
99, 689.
The complex was a green solid with a metallic lustre; νmax
-
(Nujol)/cmϪ1 1620 and 1520 (C᎐C and C᎐N, conj.), 1320
᎐
᎐
9 D. E. Ames, D. Bull and C. Takundwa, Synth. Commun., 1981, 364.
10 L. Brandsma, Studies in Organic Chemistry: Preparative Acetylenic
Chemistry, Elsevier Science Publishers B.V., Amsterdam, 1988, vol.
34, p. 220.
(N᎐CH3), 1170 and 1150 (Py+᎐CH3), 950 (Py), 815, 720 and 665
(Py᎐H, 3-subst.); λmax(CH2Cl2)/nm 264, 327, 594, 617 and 642.
11 J. G. Rodríguez, S. Ramos, R. Martín-Villamil, I. Fonseca and
A. Albert, J. Chem. Soc., Perkin Trans. 1, 1996, 541.
12 G. M. J. Schmidt, Reactivity of the Photoexcited Organic Molecule,
Wiley, New York, 1967, p. 227.
13 S. D. L’vova, Y. P. Koslov and U. I. Gunar, Zh. Obshch. Khim., 1977,
47, 1251.
Acknowledgements
We are indebted to the CAYCIT of Spain for financial support
(project no. PB92-0142-C02-01).
14 A. Altomare, G. Cascarano, C. Giacovazzo and A. Guagliardi,
Dipartimento Geomineralogico, University of Bari; M. Burla and
G. Polidori, Dipartimento Scienze della Terra, University of
Perugia; M. Camalli, SIR92, Ist Strutt. Chimica, CNR,
Monterrotondo Stazione, Roma, 1992.
15 J. M. Stewart, F. A. Kundell and J. C. Badwin, The XRAY80
System, Computer Science Center, University of Maryland, College
Park, MD, 1980.
16 M. Martinez-Ripoll and F. H. Cano, PESOS, A Computer Program
for the Automatic Treatment of Weighting Schemes, Instituto
Rocasolano, CSIC, Madrid, 1975.
17 International Tables for X-RAY Crystallography, Kynoch Press,
Birmingham, 1974, vol. 4.
References
1 Polydiacetylenes, ed. D. Bloor and R. R. Chance, NATO ASI series
E, No. 102, Matinus Nijkoff, Boston, 1985; A. E. Stiegman,
E. Graham, K. J. Perry, R. Khundkard, L. T. Cheng and J. W. Perry,
J. Am. Chem. Soc., 1991, 113, 1658, and references cited therein.
2 G. Wegner, Z. Naturforsch., B: Anorg. Chem., Org. Chem., 1969, 24,
824.
3 G. M. Carter, Y. J. Chen, M. F. Rubner, D. J. Sandman,
M. K. Thakur and S. K. Tripathy, in Nonlinear Optical Properties
of Organic Molecules and Crystals, ed. D. S. Chemla and J. Zyss,
Academic Press, New York, 1987, vol. 2, p. 85.
4 G. Wegner, J. Polym. Sci., Part B: Polym. Lett., 1971, 9, 133.
5 Y. Ozcayir, J. Asrar and A. Blumstein, Mol. Cryst. Liq. Cryst., 1984,
110, 1424.
18 M. Nardelli, Comput. Chem., 1983, 7, 95.
19 U. Fritzsche and S. Hunig, Tetrahedron Lett., 1972, 4831.
6 G. H. Milburn, A. R. Wernick, J. Tsibouklis, E. Bolton,
G. Thomson and A. Shand, Polymer, 1989, 30, 1004.
7 J. P. Ferraris, D. O. Cowan, V. Walatka and J. Perlstein, J. Am. Chem.
Soc., 1973, 95, 948.
Paper 6/05468D
Received 5th August 1996
Accepted 5th November 1996
714
J. Chem. Soc., Perkin Trans. 1, 1997