Synthesis and Structural Characterization of Ethynylene-Bridged Bisazines Featuring Various α-Substitution

Article abstract of DOI:10.1002/jhet.2122

A series of bispyridines and bispyrimidines 1a, 1b, 1c, 1d, 1e showing the heterocycles attached to both ends of an ethynylene unit and being α-substituted with chloro, tert-butylthio, and methoxy groups have been synthesized via cross-coupling technique and their crystal structures studied by X-ray diffraction analysis. Supramolecular interactions of C-H···N and π···π stacking type were found to largely dominate the structures according to the compound species. A trial was given to deduce the markedly differing temperatures of melting among the compounds from special features of the crystal structures.

Full text of DOI:10.1002/jhet.2122

Month 2014 Synthesis and Structural Characterization of Ethynylene-Bridged Bisazines
Featuring Various α-Substitution
Jörg Hübscher, Wilhelm Seichter, Thomas Gruber, Jens Kortus, and Edwin Weber *
a
a
b
b
a
a
Institut für Organische Chemie, Technische Universität Bergakademie Freiberg, Leipziger Strasse 29, D-09596
Freiberg, Germany
b
Institut für Theoretische Physik, Technische Universität Bergakademie Freiberg, Leipziger Strasse 23, D-09596
Freiberg, Germany
*
E-mail: edwin.weber@chemie.tu-freiberg.de
Received July 10, 2013
DOI 10.1002/jhet.2122
Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com).
A series of bispyridines and bispyrimidines 1a–1e showing the heterocycles attached to both ends of
an ethynylene unit and being α-substituted with chloro, tert-butylthio, and methoxy groups have been
synthesized via cross-coupling technique and their crystal structures studied by X-ray diffraction
analysis. Supramolecular interactions of C–H···N and π···π stacking type were found to largely dominate
the structures according to the compound species. A trial was given to deduce the markedly differing
temperatures of melting among the compounds from special features of the crystal structures.
J. Heterocyclic Chem., 00, 00 (2014).
INTRODUCTION
either electron withdrawing or donating groups, respectively
Scheme 1). These compounds were found to show interesting
(
Heterocycles have paved the way for a host of com-
pounds being effective in different fields of application
such as drugs [1–3], polymers [4], or complexants [5–7].
Considering the latter mode of application, linker mole-
cules suitable for the construction of so-called coordination
polymers or metal-organic framework structures based on
aza heterocycles get increasingly to a center of interest
solid state structures that are also reported and comparatively
discussed here, considering specific effects of the structural
characteristics of the molecules exercising an influence on
the supramolecular interaction modes.
RESULTS AND DISCUSSION
[8,9]. In this respect, ethynylene-linked azines have been
successfully used as linker molecules for the coordinative
oligomerization [10,11] and polymerization [12–15] of
appropriate metal ions. Moreover, in a sphere suited some-
thing different from before, respective molecules were also
tested regarding the possibility to assist solid network
formation via hydrogen bonding [16]. Among others, this
has been realized with the formation of chain-linked
capsules using intermolecular aggregation [17]. Following
a related target, terminally functionalized analogues, in
particular α-chlorinated ethynylene-bridged pyridines have
proven to be key intermediates for the synthesis of conju-
gated tectones for supramolecular nanoengineering [18].
In the present article, we describe the synthesis of five
linker-type azines composed of a central ethynylene moiety
and terminal pyridine and pyrimidine units featuring
different linkage modes (1a, 1b) as well as different kinds
and numbers of additional substituents, that is, chlorine
Synthesis. Due to the basic structure of compounds
a–1e, all being azine-terminated ethynes, their syntheses
1
follow a rather uniform preparative route starting from
iodo-substituted azines 4a–4e (Scheme 2). They suitably
meet the requirements for an intended coupling with the
ethyne moiety typical of the target compounds. These
azines, in the run-up to the synthesis, were obtained,
applying different procedures known from the literature,
except for 4c that has not been described before. Referring
to these transformations, 4a was directly iodinated using
Schlosser’s conditions [19] and isolated by fractional
crystallization from dry ethanol, while 4b was prepared
in two steps from 2-hydroxypyridine via 5-iodo-2-
hydroxypyridine (5) [20]. At this point, we advise to
perform the reaction for 5 by adding the aqueous NaOCl
solution dropwise during 2 h at 40°C instead of 0°C that
gave an increase of the yield of 12% compared with
the literature [18]. Subsequent chlorination of 5 with
(
1a, 1b, 1d), tert-butylthio (1c), or methoxy (1e) being
©
2014 HeteroCorporation

J. Hübscher, W. Seichter, T. Gruber, J. Kortus, and E. Weber
Vol 000
Scheme 1
Scheme 2
phosphorous oxychloride, successfully carried out by
Schaetzer et al. [21], can also be performed in dry
acetonitrile solution in the presence of Hünig’s base to
gain 4b effortless in good yield according to our finding.
By using the same chlorination method, 4d was
synthesized from 5-iodo-2-hydroxypyrimidine [22], which,
at the same time, is also the precursor compound for the
preparation of 4c and 4e obtained from nucleophilic
substitution with sodium 2-methylpropane-2-thiolate
and sodium methanolate [23], respectively. Subsequent
couplings of the iodoazines 4a–4e to the ethyne core
existing in the target molecules 1a–1e were performed,
applying the metal-assisted Sonogashira–Hagihara
cross-coupling procedure [24]. These couplings involve
two individual steps and have been carried out using trans-
iodide, and triphenylphosphine in diisopropylamine as the
catalytic system. To begin with, the respective iodoazines
4a–4e were coupled with TMS-mono-protected ethyne to
give the intermediate compounds 3a–3e, which, after splitting
off the TMS group, yielded the terminal acetylene derivatives
2a–2e. These were subjected to an analogous cross-coupling
reaction with the corresponding iodoazines 4a–4e leading to
1a–1e, which are new compounds, except 1b that is known
but has been synthesized on a different way [18]. On the
whole, this methodic pathway for the preparation of
symmetric ethynylene-bridged azines leads to considerable
yields in view of the multi-step synthesis (Table 1).
Regarding the IR spectra of the compounds, the fourfold
chlorinated bispyridine 1a features a broad signal at
ꢀ
1
1103 cm for the C–Cl stretching vibration, while the cor-
ꢀ
1
ꢀ1
dichlorobis(triphenylphosphine)palladium(II),
copper(II)
responding signals for 1b (1017 cm ) and 1d (1036 cm )
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Month 2014
Ethynylene-Bridged Bisazines Featuring Various α-Substitution
Table 1
Overall yields and melting points for the ethynyl-bridged bisazines 1a–1e.
that can potentially be formed are still not fundamentally
understood, asking for further investigation. Following this
idea, to study crystal structures of the present series of
compounds may open valuable information considering that
a variety of weak interactions involving X···X, C–H···X,
X···π, C–H···π, and π···π contacts are likely competing for
control of the crystal packing. Yet, compounds under
discussion show rather defined molecular structures, making
comparison reasonable. Aside from other relations, this may
also suggest a potential background regarding the question
raised with reference to the remarkably differing melting
temperatures of the compounds under discussion. Hence,
X-ray crystal structures of 1a–1e have been studied.
Relevant crystallographic data and information concerning
possible intermolecular interactions in the crystal structures
are summarized in Tables 2 and 3. Molecular structures and
packing diagrams are presented in Figures 1–8.
Synthetic
steps
Overall
yield (%)
Melting
point (°C)
Compound
1
1
1
1
1
a
b
c
d
e
4
5
5
4
5
15.7
16.7
42.4
32.6
32.9
140
230
57
205
182
sharpen and show decreasing intensity, respectively. The
1
13
H and C NMR spectra of 1a–1e largely correspond to
the expected data. A more remarkable result, however,
refers to the melting points determined for the bisazines
1
a–1e (Table 1). They differ broadly ranging between
5
7°C and 230°C. The highest melting points were found
for 1b (230°C) and 1d (205°C), both being bisazines
having the chloro substituents in linear fashion with
reference to the ethynylene bond, while 1a featuring the
chlorine atoms in angular attachment to the molecular
backbone shows a distinctly lower melting temperature of
Crystal structures of the chloro-substituted dipyridinoethynes
a and 1b. The tetrachloro-substituted dipyridylethyne 1a
crystallizes as colorless blocks of the tetragonal space group
1
I4 /acd with one fourth of the molecule in the asymmetric
1
part of the unit cell. The molecule adopts a distorted
conformation with a twist angle of 19.5° between the
aromatic rings (Fig. 1a). The bond distances within the
molecular framework resemble those of 4,4′-dipyridylethyne
being described in the literature as a component of some
co-crystals [29,30].
1
40°C. This points to specific chlorine-involved interac-
tions for 1a, on the one side, or 1b and 1d, on the other
side, in the crystalline state. Moreover, from spatial view,
the nitrogen atoms in 1b and 1d should be more easily
accessible to potential supramolecular interactions than in
1
a, pointing to the same fact. In the case of 1e with polar
Because of the irregular molecular conformation, undu-
lated layers of molecules represent the basic supramolecu-
lar aggregates of the crystal structure (Fig. 2). Because of
the steric demand of the two neighboring chlorine substit-
uents, the nitrogen atoms are excluded from hydrogen
bonding. Instead, ring motifs formed by four chlorine
atoms [C(1)–Cl(1)···Cl(1) 3.560(1) Å, 151.6(1)°] represent
the basic supramolecular contact mode within the molecu-
lar layer. In order to give a more detailed impression of this
remarkable chlorine interaction, the electron density based
on density functional theory was calculated using quantum
espresso [31]. Figure 3 shows the respective cutout of the
electron density map for the crystal structure of 1a. Never-
theless, this particular type of cyclic Cl···Cl interaction is
not an unknown phenomenon but has previously been
observed also in a few aromatic structures [32,33] including
a chlorine-containing bisazine [34]. Moreover, the chlorine
atoms of the present structure take part in weak C–H···Cl
contacts [35] [C(2)–H(2)···Cl(1) 2.99 Å, 140°]. In addition,
offset face-to-face arene interactions [36] with a distance of
approx. 3.4 Å between the interacting aromatic rings
stabilize the crystal structure along the stacking axis of
molecular layers.
methoxy groups linearly linked to the backbone structure,
the melting point is moderately high (182°C). The lowest
melting point applies to 1c (57°C) being a reasonable
implication of the bulky tert-butyl groups at the molecular
periphery. In order to understand the solid state structures
of the compounds 1a–1e including argumentation of the
supposed relations raised earlier, single-crystal X-ray
structures have been performed.
X-ray crystallography.
It is a well-known fact that
supramolecular interactions such as hydrogen bonding [25],
halogen bonding [26], and π···π contacts [27] are driving
forces for the packing motif generated in a crystal. This
is of relevance because the physical and physicochemical
properties of a solid material are a direct consequence
having both scientifically and economically great bearing,
for example, in the preparation of pharmaceutical products
and pigments, in many cases containing N-heterocycles and
chlorine atoms in the molecular structure. Previous studies
have shown that allowing a certain degree of predictability
as far as the solid state structure is concerned, both
knowledge of the supramolecular bonding capacity of the
component building blocks and a controlled overall
structure of the test molecule are promising. This is behind
the concept of what is called “crystal engineering” [28].
However, many facts in particular connected with the
competition problem between different modes of interaction
The dichloro analogous derivative 1b crystallizes as
colorless plates of the triclinic space group P-1 with
Z = 1. A perspective view of the molecular structure is
depicted in Figure 1b. The molecule adopts a slightly
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J. Hübscher, W. Seichter, T. Gruber, J. Kortus, and E. Weber
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Month 2014
Ethynylene-Bridged Bisazines Featuring Various α-Substitution
Table 3
Geometric parameters for intermolecular contacts in compounds studied in this article.
Distance (Å)
Angle (°)
D–H···A
C–X···A
D–H
C–X
D···A
C···A
H···A
X···A
Atoms involved
Symmetry
1a
C(2)–H(2)···Cl(1)
C(1)–Cl(1)···Cl(1)
C(1)–Cl(1)···cg(A)
ꢀ3/4 + y, 7/4 – x, 1/4 ꢀ z
7/4 ꢀ y, 3/4 + x, 1/4 ꢀ z
x, 2 ꢀ y, 1/2 ꢀ z
0.95
1.731(1)
1.731(1)
3.649(1)
3.482(1)
2.99
140
151.6(1)
66.50(2)
3.560(1)
3.789 (1)
3.823(1)
a
a
cg(A)···cg(A)
x, 2 ꢀ y, 1/2 ꢀ z
1b
C(1)–Cl(1)···Cl(1)
C(4)–H(4)···N(1)
cg(A)···cg(A)
ꢀx, 2 ꢀ y, ꢀz
1 + x, ꢀ1 + y, z
1.738(2)
0.93
3.349 (2)
2.51
3.841(2)
160.6(1)
161
3.409(2)
1c
C(13)–H(13A)···N(1)
C(12)–H(12C)···N(1)
C(16)–H(16C)···N(3)
C(17)–H(17A)···N(3)
C(8)–H(8)···N(4)
x, y, z
x, y, z
x, y, z
x, y, z
ꢀ1 + x, y, z
1/2 + x, 3/2 ꢀ y, 1/2 + z
1 ꢀ x, 2 ꢀ y, 2 ꢀ z
0.98
0.98
0.98
0.98
0.95
0.98
3.159(1)
3.139(1)
3.186(1)
3.130(1)
3.302(1)
3.641(1)
2.48
2.45
2.50
2.44
2.42
2.69
3.9384(5)
126
127
127
127
155
163
a
C(16)–H(16A)···cg(A)
a
cg(B)···cg(B)
1d
C(4)–H(4)···Cl(1)
C(1)–Cl(1)···cg(A)
C(2)–H(2)···N(2)
cg(A)···cg(C≡C)
1x ,/ 2y ,ꢀzx, ꢀ1/2 + y, 1/2 ꢀ z
ꢀ1/2 + x, 3/2 ꢀ y, 1/2 + z
2 ꢀ x, 2 ꢀ y, ꢀz
0.93
1.729(1)
0.93
3.462(2)
3.00
3.5366(7)
2.80
112
90.51(5)
152
a
3.645( )
3.593(2)
1e
C(6)–H(6C)···O(1)
C(4)–H(4)···N(1)
C(1)–O(1)···O(1)
cg(A)···cg(A)
1 + x, y, z
0.96
0.93
1.333(2)
3.255(2)
3.444(2)
2.69
2.67
2.864(2)
3.910(2)
151
146
145
ꢀ1 + x, 3/2 ꢀ y, ꢀ1/2 + z
1 ꢀ x, 2 ꢀ y, ꢀz
a
cg means center of the aromatic rings. Ring A: N1–C1–C2–C3 (1a), C1–N1–C2–C3–C4–C5 (1b), N1–C1–C2–C3–C4–N2 (1c–1e). Ring B: C7–C8–
N3–C9–N4–C10 (1c).
Cl1
(a)
(b)
C1
C4
C5
N1
N1
C2
C3
Cl1 C1
C3
C4
C6
C2
Figure 1. Perspective views of 1a (a) and 1b (b), including the numbering scheme of atoms. Thermal ellipsoids are drawn at 50% (1a) and 30%
1b) probability level.
(
distorted conformation along its main axis, which is
obvious from the bond angles around the substituted ring
carbon atoms C(1) and C(3) [N(1)–C(1)–Cl(1) 115.7
the Cl···Cl interactions meet the conditions of a type I
(head-on) contact very well [39].
Crystal structures of the substituted dipyrimidinoethynes
(2) Å, C(4)–C(3)–C(6) 122.1(2)°]. The bond lengths agree
1c–1e. Perspective views of the molecular structures
with those of the unsubstituted parent molecule [37]. The
crystal structure (Fig. 4) is composed of infinite C–H···N
bonded [38] strands [C(4)–H(4)···N(1) 2.51 Å, 161°],
which are further associated via Cl···Cl interactions [39]
of 1c–1e are displayed in Figure 5. The bond lengths
within the diarylethynylene framework of the molecules
are in the range of those found for the unsubstituted parent
compound 1,2-bis(pyrimid-5-yl)ethyne [17]. This means
that substituents of different electronic nature hardly affect
bond distances. The t-butylthio-substituted compound 1c
[
C(1)–Cl(1)···Cl(1) 3.349(2) Å, 160.1(1)°] to form two-
dimensional molecular networks extending parallel to the
crystallographic 112 plane. According to their geometry,
exists in the monoclinic space group P2 /n (Z = 4) with the
1
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J. Hübscher, W. Seichter, T. Gruber, J. Kortus, and E. Weber
Vol 000
a
b
Figure 2. Packing structure of 1a viewed down the crystallographic c-axis. Broken lines represent C–H···Cl and Cl···Cl contacts. The tetra-chlorine-
containing ring motif is indicated by shading.
[d(C···N) 3.130(1), 3.186(1) Å]. Crystals of the methoxy-
and chlorine-substituted derivatives 1e and 1d have the
monoclinic space groups P2 /c and P2 /n, respectively, with
1
1
Z = 2; that is, the molecules are located on symmetry centers.
Hence, the molecular backbone is of approximate planarity.
In the crystal structure of 1c, the molecule adopts a
distorted conformation that may be ascribed to packing ef-
fects caused by the bulky tert-butyl terminal groups. As
shown in Figure 6, the crystal structure is composed of
C–H···N bonded molecular tapes [C(8)–H(8)···N(4)
2
.42 Å, 155°] running along the crystallographic a-axis.
Within these aggregates, molecules are linked in an
asymmetric fashion because only one nitrogen of each
molecule is involved in intermolecular hydrogen bonding.
Also, the aromatic rings are involved in a different way
in intermolecular interactions. The mean distance of
approx. 3.30 Å between the aromatic units of adjacent
molecular tapes suggests the presence of offset face-to-face
π···π arene interactions. In addition, the crystal structure is
stabilized by multiple C–Ht-butyl···πarene contacts [25].
The crystal structure of 1d is constructed of molecular
stacks extending along the a-axis (Fig. 7). Within a given
stack, consecutive molecules are displaced in the direction
of their longitudinal axes. In this arrangement, the ethynylene
unit of each molecule is located between the aromatic
rings of neighboring molecules indicating the presence
of πarene···πethyne interactions [cg(A)···cg(C≡C) 3.593(2) Å].
Molecules of neighboring stacks are inclined at approxi-
mately 75° to one another, possibly to realize a close packing
Figure 3. Cutout of the electron density map for the crystal structure
of 1a. The electron density was calculated using a GGA exchange-
correlation functional after Perdew–Burke–Ernzerhof [49]. Electron
ꢀ
3
density values are given in e · a .
0
molecule located in a general position. The twist angle
between the aromatic rings is 12.0(1)°. The molecular
conformation is determined by four intramolecular C–H···N
hydrogen bond type contacts involving tert-butyl hydrogens
as donors and the nitrogens N(1) and N(3) as acceptor sites
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Ethynylene-Bridged Bisazines Featuring Various α-Substitution
b
c
a
Figure 4. Packing structure of 1b. C–H···N and halogen interactions are marked by broken lines.
C13
C11
C14
C12
N1
C2
S1
C1
A
C4
C10
C3
N4
N2
(
a)
C5
C6
C9
C7
B
S2
C8
C17
N3
C15
C18
C16
N1
C6
C1
C2
N1
C2
Cl1
C1
N2
O1
N2
C3
C3
C4
C5
C4
C5
(b)
(c)
Figure 5. Perspective views of 1c (a), 1d (b), and 1e (c), including the numbering scheme of atoms. Thermal ellipsoids are drawn at 50% (1c) and 30%
1d/e) probability level.
(
structure. In a similar fashion as in the aforementioned case,
one of the pyrimidine nitrogens is involved in intermolecular
association giving rise to weak C–H···N hydrogen bond
[C(2)–H(2)···N(2) 2.80Å, 152°] that interlinks the molecular
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J. Hübscher, W. Seichter, T. Gruber, J. Kortus, and E. Weber
Vol 000
a
c
b
Figure 6. Packing structure of 1c. All hydrogen atoms except those involved in C–H···N interaction (broken lines) are omitted for clarity.
b
c
Figure 7. Packing structure of 1d viewed down the crystallographic a-axis. Broken lines represent hydrogen bond type interactions.
stacks. Noteworthy enough, there is no short contact in the
structure to be assigned a Cl···Cl interaction.
A view of the crystal structure of 1e along the crystallo-
graphic b-axis reveals a layered packing of molecules
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Month 2014
Ethynylene-Bridged Bisazines Featuring Various α-Substitution
c
a
b
Figure 8. Packing structure of 1e. Broken lines represent hydrogen bond type and O···O contacts.
(
Fig. 8). Each layer is composed of parallel C–H···N bonded
and the bulkily tert-butylthio-substituted molecule 1c a
moderate deviation from coplanarity that might be a result
of packing effects caused by the specific substitutions. An-
other active part in the conformational behavior of 1c may
be ascribed to the intramolecular H-bonds of inverse bifur-
cated nature being formed between methyl groups and one
of the pyrimidine nitrogens of both terminals of the mole-
cule, thus preventing the tert-butyl groups from rotation.
molecular strands in which only one of the pyrimidine nitro-
gens participates in this contact [C(4)–H(4)···N(1) 2.67 Å,
1
46°]. A remarkable O···O distance of 2.864(2) Å between
molecules of adjacent strands falling short of twice the van
der Waals radius of oxygen (1.52 Å) suggests the presence
of weak intermolecular O···O contacts. However, a couple
of structures showing this particular type of interaction
mainly supported by phenolic oxygen atoms located in the
β-position of one or more nitrogen atoms can already be
found in the literature [40–42]. Offset face-to-face arene
interactions with a distance of approx. 3.5 Å between the
planes of adjacent molecules stabilize the packing structure
along the stacking axis of the supramolecular layers.
1
Although C–H···N hydrogen bonding of ring type R ð6Þ
2
is known on principle, a similar situation involving a tert-
butyl group has not been described before.
Regarding the supramolecular interactions, C–H···N
contacts play a dominating role in all structures excepting
1a where the nitrogens seem to be shielded from interac-
tion by the neighboring chlorines. In the crystal structures
of 1b–1e, these C–H···N contacts give rise to different
modes of supramolecular netting. That is, in the cases of
COMPARATIVE REFLECTION AND
CONCLUSIONS
1
b and 1c, tapes of parallel aligned molecules are formed
Using a Pd-catalyzed coupling procedure as key step of
the synthesis, a series of five bispyridine and bispyrimidine
derivatives featuring the heterocycles attached to a central
acetylene unit and having chlorine, tert-butylthio, or
methoxy groups as additional substituents were success-
fully prepared. These compounds not only show promising
structural property for the potential use as linker-type
molecules in the construction of coordination polymers or
related supramolecular architectures but offer also an inter-
esting cooperative study of their solid state structures,
giving rise to conclusions that should be of use in this field
of heterocyclic chemistry.
with each molecule interacting in both directions only with
one neighboring molecule, while in the crystals of 1d and
1e, the structures are more complex because the interacting
molecules are displaced against each other, creating hydro-
gen bonds to four different neighbors. The tapes of 1b are
linked via head-on Cl···Cl contacts to yield planes that
stack in aromatic π···π interaction mode. Also, in 1c aro-
matic π···π stacking, interactions and weak C–H···π con-
tacts participate in the stabilization of the tapes. In 1d,
the structure is stabilized by additional Cl···π, C–H···Cl,
and π(arene)···π(ethynyl) contacts, and 1e shows plane for-
mation created by a combination of the C–H···N interaction
with linear O···O contacts giving rise to stacking of the
planes. Hence, all the structures of 1b–1e are dominated
by C–H···N and π···π stacking contacts including supportive
Considering the molecular conformations of the com-
pounds, the heterocyclic rings are largely coplanar and
show only in the cases of the tetrachloro derivative 1a
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(
9 : 1)]. Elemental analysis: Hanau vario MICRO cube.
interactions such as Cl···Cl (1b), weak C–H···π (1c), Cl···π
and C–H···Cl (1d), or O···O type (1e) according to the
compound species.
Another result follows from comparison of the crystal
structures of chloro-substituted compounds 1a, 1b, and
Column chromatography: silica gel 60 (0.040–0.063 mm,
Merck). TLC analysis: aluminum sheets precoated with silica
gel 60 F254 (Merck).
Reagents and materials were obtained from commercial sup-
pliers (Fisher Scientific, ABCR, Aldrich) and were used without
further purification. The solvents were purified using standard
procedures. Solvents for the Sonogashira–Hagihara coupling
reactions were deoxygenated prior to use by ultrasound (20 min)
while bubbling argon through the solution.
1
d. Although in all their structures the chlorine atoms are
involved in intermolecular interactions, modes of contact
are different; that is, weak C–H···Cl and Cl···π contacts in
the case of 1d while both in 1a and 1b the Cl atoms give
rise to Cl···Cl interactions. Nevertheless, in 1b, these
Cl···Cl contacts are type I (head-on) mode but in 1a type
II (side-on) mode, suggesting specific exerting of influence
of the chlorine’s disposition and vicinity in the molecule on
the halogen interaction. In the case of 1a, this leads to the
remarkable formation of a square of four contacting halo-
gen atoms nevertheless, which is typical enough recently
being suggested as a potential supramolecular synthon of
halogen interaction in crystals [43].
2
-Hydroxy-5-iodopyridine (5). To 34.9 g (0.4 mol) 2-
hydroxypyridine dissolved in 650mL methanol, 56.0g (0.4mol)
sodium iodide and 14.7g (0.4 mol) sodium hydroxide were added
at 0°C. Following, 677.7 g (0.4 mol) of an aqueous sodium
hypochlorite solution (4% active chlorine) was added dropwise
over 2 h at 40°C, and the mixture was stirred for another 2 h at
room temperature. After that, 350 mL of a 0.6M aqueous sodium
thiosulfate solution was added, and the mixture was neutralized
with 300 mL of aqueous 1.4 M hydrochloric acid. Evaporation of
the methanol in vacuo yielded a white precipitate. This was
separated from the liquid phase and washed with water to give
Correlations between the marked differences in melting
points among the compounds mentioned earlier and their
crystal structures are not readily obvious but might be
reflected as follows. In the structures of compounds 1b,
4
8.6g (60%) of the pure product, mp 190°C (Lit.: 190–191°C
1
4
[
20]), H NMR (DMSO-d ): δ 8.60 (d, J= 2.2 Hz, 1 H, phenyl),
6
3
4
3
7.92 (dd, J=8.3Hz, J= 2.2 Hz, 1 H, phenyl), 7.14 (d, J=8.3Hz,
1
3
1 H, phenyl); C NMR (DMSO-d
21.6, 64.4.
,6-Dichloro-4-iodopyridine (4a). 7.5 g (0.05 mol) 2,6-
): δ 161.9, 147.6, 140.0,
6
1
1
d and 1e, showing the highest temperature of melting,
2
three-dimensional networks involving distinct C–H···N
and π···π interactions supported by additional heteroatom
contacts are observed. However, 1c, having the lowest
melting point, yields only half as much of C–H···N con-
tacts per molecule because only one of the heteroaromatic
rings is included and only weak C–H···π contacts are
present for additional support of the structure. The struc-
ture of the bisazine 1a with moderate temperature of
melting between that of 1c and the other compounds does
not show the prior C–H···N contacts. In this connection,
it is also interesting to note that just the compounds 1a
and 1c, having the lowest melting points, are those
featuring an interplanar angle of the azine rings consider-
ably different from coplanarity, which suggests some strain
in the packing possibly becoming apparent in lower
temperature of melting because of destabilization of the
crystal lattice. The packing densities (KPI index [44] %)
for all crystals were calculated as 71.3 (1a), 70.6 (1b),
dichloropyridine was dissolved in 85mL tetrahydrofuran and
cooled down to ꢀ75°C. To this solution, 32 mL of a 1.6 M
n-BuLi solution in n-hexane was added, and the resulting
mixture was stirred for 45min at ꢀ75°C. Following, a solution of
13.0g (0.1mol) iodine in 24 mL tetrahydrofuran was added
dropwise, and stirring was continued for another 15 min at ꢀ75°C.
The solution was allowed to warm to room temperature and
treated with 43 mL of aqueous 0.6 M sodium thiosulfate and
water. After removal of the solvent, a mixture consisting of
2
,6-dichloro-4-iodopyridine and 2,6-dichloro-3-iodopyridine
as by-product was obtained. Fractional crystallization from
dry ethanol yielded 4.1 g of the title compound as white,
crystalline solid (30%), mp 162°C (Lit.: 162–164°C [19]),
1
13
H NMR (CDCl
3 3
): δ 7.66 (s, 1 H phenyl); C NMR (CDCl ):
δ 150.7, 131.5, 107.6.
General procedure for preparation of 4b and 4d. The
respective 2-hydroxyazine was suspended in dry acetonitrile,
and a 1.3 times excess of phosphorous oxychloride was added
in one bulk. Subsequently, the equimolar amount of N,N-
diisopropylethylamine was added dropwise, and the reaction
mixture was stirred under reflux (time of stirring as specified for
each compound). After cooling to approx. 40°C, an equal
volume of water was added dropwise over 20 min. Both the
resulting residue and the filtrate were extracted with ethyl
acetate. To the combined organic layers, water (10% by volume
of the organic phase) was added, and the resulting inhomogenous
mixture was evaporated until the inner temperature reached 85°C.
Cooling to room temperature yielded the crude product as a
white precipitate, which was purified by crystallization from
n-hexane. Specific details for each compound are specified in
the following sections.
6
6.6 (1c), 70.6 (1d), and 72.1 (1e). Used as a further
potential way of argumentation, they indicate a distinctly
lower value for 1c compared with the other compounds,
which is in agreement with the particularly low melting
temperature of 1c, but more clearly perceptible correlation
seems hardly readable from the data.
EXPERIMENTAL
General. Melting points: Kofler melting point microscope
uncorrected). IR: Nicolet FT-IR 510. H and C NMR
internal standard TMS, δ in ppm): Bruker AVANCE DPX 500.
MS (ESI): Varian 320 MS [CID 100 V, solvent: methanol/water
2-Chloro-5-iodopyridine (4b). 10.0 g (45.5 mmol) 5-iodo-2-
hydroxypyridine (5) was reacted in 80 mL acetonitrile for 4 h
1
13
(
(
1
yielding 8.0 g (74%), mp 98°C (Lit.: 98°C [45]), H NMR
4
(CDCl ): δ 8.60 (d, 1 H, J = 2.2 Hz, phenyl), 7.92 (dd, 1 H,
3
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
Ethynylene-Bridged Bisazines Featuring Various α-Substitution
3
4
3
4
3
J = 8.3 Hz, J = 2.2 Hz, phenyl), 7.14 (d, 1 H, J = 8.3 Hz,
J = 2.1, phenyl), 7.27 (d, 1 H, J = 8.3 Hz, phenyl), 0.26 (s, 9 H,
13
13
phenyl); C NMR (CDCl ): δ 155.6, 150.9, 146.7, 126.1, 90.7.
CH3); C NMR (CDCl ): δ 152.4, 150.5, 141.2, 123.7, 119.1,
3
3
2
-Chloro-5-iodopyrimidine (4d). 50.0 g (0.2 mol) 5-iodo-2-
100.0, 99.6, ꢀ0.3.
hydroxypyrimidine were reacted in 270 mL acetonitrile for 20 h
using the chlorination procedure yielding 48.5 g (90%, Lit.:
2% [22]), mp 133°C (Lit.: 129–130°C [46]), H NMR
DMSO-d ): δ 9.04 (s, 2 H, phenyl); C NMR (DMSO-d ): δ
2-(t-Butylthio)-5-(trimethylsilylethynyl)pyrimidine (3c). 10.0 g
(34.0 mmol) 2-(t-butylthio)-5-iodopyrimidine (4c), 3.5 g (35.5 mmol)
trimethylsilyl acetylene, and the catalyst in a mixture of 240 mL
diisopropylamine and 240 mL of tetrahydrofuran were used. After
stirring at room temperature for 6 h, the reaction was complete.
1
7
(
1
1
3
6
6
65.5, 159.0, 93.0.
2
-(t-Butylthio)-5-iodopyrimidine (4c). To 0.8 g (21.0mmol)
2
Purification by column chromatography (SiO ; n-hexane/ethyl
of a 60% dispersion of sodium hydride in mineral oil
dissolved in 50mL of dry dimethyl formamide, 1.9 g (21.0mmol)
acetate; 20 : 1) yielded 6.7 g (75%) of a white solid, mp 28°C; IR:
ꢀ
1
1
ArCH 2957, CC 2161, CN 1572, CH 1396 cm
(CDCl ): δ 8.53 (s, 2 H, phenyl), 1.61 (s, 9 H, CH ), 0.26 (s, 9 H,
): δ 171.9, 158.8, 113.9, 101.0, 98.3, 47.7,
; H NMR
2
-methylpropane-2-thiol was added dropwise. The mixture was
stirred for 30 min at room temperature. Then, 5.0 g (21.0 mmol)
-chloro-5-iodopyrimidine (4d) was added, and the resulting
3
3
13
3 3
CH ); C NMR (CDCl
29.8, 29.8; MS: m/z 265 (M ).
+
2
suspension was stirred for 2 h at room temperature. The solvent
was removed in vacuo, and the residue treated with 100 mL of
water and extracted with diethyl ether. Purification by column
2-Chloro-5-(trimethylsilylethynyl)pyrimidine (3d). 2.0 g
(8.4 mmol) 2-chloro-5-iodopyrimidine (4d), 0.9 g (9.0 mmol)
trimethylsilyl acetylene, and the catalyst in 60 mL diisopropylamine
were used. After stirring at room temperature for 12 h, the reaction
chromatography (SiO
2
; n-hexane/ethyl acetate; 50 : 1) yielded
5
3
8
1
.3 g (85%) of a white solid, mp 38°C, IR: CH 3229, ArCH
was complete. Purification by recrystallization from n-hexane
ꢀ
1
1
1
079, CN 1698, CH 1394, CI 1071 cm ; H NMR (CDCl ): δ
yielded 1.8 g (99%) of a white solid, mp 48°C, H NMR (CDCl ):
3
3
1
3
13
.66 (s, 2 H, phenyl), 1.59 (s, 9 H, CH3). C NMR (CDCl ): δ
δ 8.70 (s, 2 H, phenyl), 3.47 (s, 1 H, CH); C NMR (CDCl ): δ
3
3
+
71.4, 161.5, 86.1, 47.2, 29.5; MS: m/z 295 (M ).
161.7, 160.1, 117.2, 85.6, 75.7.
5
-Iodo-2-methoxypyrimidine (4e). To a suspension of 8.8 g
2-Methoxy-5-(trimethylsilylethynyl)pyrimidine (3e). 4.0 g
(17.0 mmol) 5-iodo-2-methoxypyrimidine (4e), 1.7 g (17.0 mmol)
trimethylsilyl acetylene, and the catalyst in 120 mL diisopropylamine
were used. After stirring at room temperature for 3 h, the reaction
(
36.8 mmol) 2-chloro-5-iodopyrimidine (4d) in 40 mL of dry
methanol, a methanolic sodium methanolate solution [obtained
from 1.0 g (43.5 mmol) sodium in 50 mL dry methanol] was
added dropwise. After having stirred for 2 h at room temperature,
the mixture was evaporated in vacuo. The residue was treated
with 60mL of water and extracted with methylene chloride. The
combined organic layers were dried over sodium sulfate and
2
was complete. Purification by column chromatography (SiO ;
n-hexane/ethyl acetate; 9 : 1) yielded 3.0 g (87%) of a white
1
solid, mp 42°C, H NMR (CDCl ): δ 8.58 (s, 2 H, phenyl),
3
1
3
4.03 (s, 3 H, CH ), 0.26 (s, 9 H, CH ); C NMR (CDCl3):
3
3
evaporated to dryness to give 8.2 g (94%, Lit.: 80% [23]) of a
δ 164.2, 163.9, 161.7, 112.8, 99.9, 97.9, 55.2, 0.3.
1
white solid, mp 125°C, H NMR (CDCl
3
): δ 8.65 (s, 2 H,
General procedure for cleavage of the trimethylsilyl group.
To the TMS-protected acetylene dissolved in acetonitrile,
potassium hydroxide at 5 M aqueous solution was added at 0°C.
The solution was stirred for 15min at this temperature and poured
into water. In the case of precipitation, the solid was separated,
washed with water, and dried on air. Otherwise, the resulting
1
3
phenyl), 3.99 (s, 3H, CH
59.0, 93.0.
Sonogashira–Hagihara coupling procedure. The respective
3
); C NMR (CDCl ): δ 165.5,
3
1
aryl iodide and the corresponding terminal alkynyl component
were dissolved in a degassed mixture of diisopropylamine and
tetrahydrofuran. To this solution, the catalyst, being composed
of triphenylphosphine (2 mol-%), copper(I) iodide (3 mol-%),
and trans-dichlorobis-(triphenylphosphine)palladium(II) (2 mol-%),
was added and the mixture stirred until completion of the
reaction (TLC analysis). Evaporation of the solvent followed
by column chromatography and/or crystallization yielded the
pure compounds. Specific details for each compound are
given in the following sections.
2 4
solution was extracted with diethyl ether, dried (Na SO ), and
evaporated. Purification was accomplished by further extraction or
sublimation. Specifications for each compound are given in the
following sections.
2,6-Dichloro-4-ethynylpyridine (2a). 2.1 g (8.5 mmol) 2,6-
dichloro-4-(trimethylsilylethynyl)pyridine (3a) in 50 mL acetonitrile
and 17 mL of the KOH solution was used. Purification by
sublimation at 80°C (15 Torr) yielded 1.4 g (93%) of a white solid,
1
2
,6-Dichloro-4-(trimethylsilylethynyl)pyridine (3a). 5.0 g
mp 86°C, H NMR (CDCl
3
): δ 7.32 (s, 2 H, phenyl), 3.42 (s, 1 H,
13
(
18.3 mmol) 2,6-dichloro-4-iodopyridine (4a), 1.9 g (19.0 mmol)
CH); C NMR (CDCl
3
): δ 150.8, 135.2, 125.1, 84.6, 78.6.
trimethylsilyl acetylene, and the catalyst in a mixture of 120 mL
diisopropylamine and 120 mL tetrahydrofuran were used. After
stirring for 3 h at room temperature, the reaction was complete.
2-Chloro-5-ethynylpyridine (2b). 4.2 g (20.0 mmol) 2-chloro-
5-(trimethylsilylethynyl)pyridine (3b) in 40 mL acetonitrile and
40 mL of the KOH solution was used. Purification by extraction
with diethyl ether yielded 2.1 g (75%) of a white solid, mp 82°C,
Purification by column chromatography (SiO
acetate; 50 : 1) yielded 2.4 g (54%) of a colorless oil, H NMR
2
; n-hexane/ethyl
1
1
4
H NMR (CDCl
(dd, 1 H, J = 8.2 Hz, J = 2.3 Hz, phenyl), 7.30 (d, 1 H,
3
): δ 8.49 (d, 1 H, J = 2.3 Hz, phenyl), 7.72
13
3
4
(
(
CDCl ): δ 7.28 (s, 2 H, phenyl), 0.26 (s, 9 H, CH ); C NMR
3
3
3
13
CDCl ): δ 151.3, 136.7, 125.7, 104.2, 99.8, 0.0.
J = 8.2 Hz, phenyl), 3.28 (s, 1 H, CH); C NMR (CDCl ): δ
3
3
2
-Chloro-5-(trimethylsilylethynyl)pyridine (3b). 9.0 g
152.4, 150.5, 141.2, 123.7, 119.1, 100.0, 99.6, ꢀ0.3.
(
37.7 mmol) 2-chloro-5-iodopyridine (4b), 3.9 g (40.0 mmol)
2-(t-Butylthio)-5-ethynylpyrimidine (2c). 6.0 g (22.7 mmol)
2-(t-butylthio)-5-(trimethylsilylethynyl)pyrimidine (3c) in 90 mL
acetonitrile and 45mL of the KOH solution was used. Purification
by extraction with diethyl ether yielded 4.2 g (96%) of a white
solid, mp 32°C, IR: CH 3229, ArCH 2961, CC 2112, CN 1571,
trimethylsilyl acetylene, and the catalyst in a mixture of
50 mL diisopropylamine and 250 mL tetrahydrofuran were used.
After reflux for 4 h, the reaction was complete. Purification by
column chromatography (SiO ; n-hexane/ethyl acetate; 20: 1)
yielded 5.9 g (75%) of a white solid, mp 59°C, H NMR (CDCl
2
2
1
ꢀ1
1
3
):
δ 8.46 (d, 1 H, J = 2.1 Hz, phenyl), 7.68 (dd, 1 H, J = 8.3 Hz,
CH 1398cm ; H NMR (CDCl
3
): δ 8.57 (s, 2 H, phenyl), 3.33
4
3
13
3 3
(s, 1 H, CH), 1.62 (s, 9 H, CH ); C NMR (CDCl ) δ 172.7,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

J. Hübscher, W. Seichter, T. Gruber, J. Kortus, and E. Weber
Vol 000
1.9 g
+
1
59.0, 112.9, 83.1, 77.1, 47.8, 29.9; MS: m/z 193 (M ); Anal.
5,5′-Ethyn-1,2-diyl-bis-(2-chloropyrimidine) (1d).
Calcd. for C H N S (192.07): C, 62.46; H, 6.29; N, 14.57; S,
(8.0 mmol) 2-chloro-5-iodopyrimidine (4d), 1.3 g (9.4 mmol)
2-chloro-5-ethynylpyrimidine (2d), and the catalyst in a
mixture of 60mL diisopropylamine and 60mL tetrahydrofuran
were used. After refluxing for 8 h, the reaction was complete.
10 12 2
1
6.68; Found: C, 62.39; H, 6.45; N, 14.69; S, 16.74%.
-Chloro-5-ethynylpyrimidine (2d). 4.0 g (4.8 mmol) 2-
2
chloro-5-(trimethylsilylethynyl)pyrimidine (3d) in 15 mL
acetonitrile and 10 mL of the KOH solution was used.
Purification by extraction with diethyl ether yielded 2.3 g
Purification by column chromatography (SiO ; n-hexane/ethyl
2
acetate; 2 : 1) yielded 1.4 g (61%) of a yellow solid, mp 205°C,
ꢀ
1
(
2
60%) yellow needles, mp 140°C, IR: CH 3212, ArCH 3037, CC
IR: ArCH 3037, CN 1730, CC 1587, 1527, CCl 1036 cm ;
ꢀ
1
1
1
13
107, CN 1568, CCl 1036 cm ; H NMR (CDCl
3
): δ 8.70 (s, 2
H NMR (DMSO-d
6
): δ 8.87 (s, 4 H, phenyl); C NMR (DMSO-
1
3
+
H, phenyl), 3.47 (s, 1 H, CH); C NMR (CDCl ): δ 161.7, 160.1,
1
d ): δ 160.1, 158.7, 115.7, 87.8; MS: m/z 249 (M + H ); Anal.
3
6
+
17.2, 85.6, 75.7; MS: m/z 138 (M ). Anal. Calcd. for C H ClN
Calcd. for C H Cl N (249.98): C, 47.84; H, 1.61; N, 22.32;
6
3
2
10
4
2 4
(
2
138): C, 52.01; H, 2.18; N, 20.22; Found: C, 52.72; H,
.14; N, 19.36%.
-Methoxy-5-ethynylpyrimidine (2e).
Found: C, 48.24; H, 1.60; N, 21.90%.
5,5′-Ethyn-1,2-diyl-bis-(2-methoxypyrimidine) (1e). 1.7 g
(7.0 mmol) 5-iodo-2-methoxypyrimidine (4e), 1.0 g (7.5 mmol)
2-methoxy-5-ethynylpyrimidine (2e), and the catalyst in a
mixture of 75mL of diisopropylamine and 75ml tetrahydrofuran
were used. After refluxing for 30min, the reaction was complete.
2
6.0 g (4.9 mmol) 2-
methoxy-5-(trimethylsilylethynyl)pyrimidine (3e) in 20 mL
acetonitrile and 10 mL of the KOH solution was used.
Purification by extraction with diethyl ether yielded 1.6 g (60%)
of a white solid, mp 82°C, H NMR (CDCl
1
3
): δ 8.61 (s, 2 H,
Purification by column chromatography (SiO
acetate; 2 : 1) yielded 1.2 g (70%) of a white solid, mp 182°C, IR:
2
; n-hexane/ethyl
13
3
phenyl), 4.04 (s, 3 H, CH ), 3.65 (s, 1 H, CH); C NMR
ꢀ
1
(
CDCl ): δ 164.2, 161.9, 161.2, 111.6, 82.2, 77.0, 55.2.
ArCH 3015, 2993, CH 2942, CC 1597, 1530, CO 1287 cm ;
3
1
Synthesis of 1a–1e.
The coupling procedure as described
H NMR (CDCl ): δ 8.67 (s, 4 H, phenyl), 4.07 (s, 3 H, CH );
3
3
13
for preparation of 3a–3e applies. Specific details for each
compound are given in the following sections.
C NMR (CDCl
3
): δ 164.2, 161.1, 111.9, 87.2, 55.2; ms: m/z
+
242 (M ); Anal. Calcd. for C12
10 4 2
H N O (242.08): C, 59.50;
4
,4′-Ethyn-1,2-diyl-bis-(2,6-dichloropyridine) (1a).
4.5 mmol) 2,6-dichloro-4-iodopyridine (4a), 0.8 g (4.7 mmol)
,6-dichloro-4-ethynylpyridine (2a), and the catalyst in a
1.2 g
H, 4.16; N, 23.13; Found: C, 59.47; H, 3.88; N, 22.83%.
(
2
X-ray structure determination.
Crystals suitable for
single-crystal X-ray diffraction studies were obtained by slow
cooling of solutions of the respective compounds in chloroform.
Information concerning the crystallographic data and the
refinement calculations of the two compounds is summarized in
Table 1. The intensity data were collected on a Bruker APEX II
diffractometer with MoKα radiation (λ = 0.71073 Å) using ω and
φ scans. Intensities were corrected for background, Lorentz, and
polarization effects. Preliminary structure models were derived
by an application of direct methods [47] and were refined by
mixture of 30 mL diisopropylamine and 30 mL tetrahydrofuran
were used. After stirring for 4 h at room temperature, the
reaction was complete. Purification by column chromatography
SiO ; n-hexane/ethyl acetate; 20 : 1) yielded 0.8 g (56%) of a
white solid, mp 140°C, IR: ArCH 3107, 3072, CC, NC 1575,
(
2
ꢀ
1
1
1
521, CCl 1103 cm
;
H NMR (CDCl
phenyl); C NMR (CDCl ): δ 151.2, 134.1, 124.7, 90.2; MS:
m/z 318 (M ); Anal. Calcd. for C H Cl N (317.99): C, 45.33;
3
): δ 7.38 (s, 4 H,
13
3
+
1
2
4
4 2
2
H, 1.27; N, 8.81; Found: C, 45.55; H, 1.19; N, 8.64%.
,5′-Ethyn-1,2-diyl-bis-(2-chloropyridine) (1b).
9.2 mmol) 2-chloro-5-iodopyridine (4b), 1.3 g (9.6 mmol)
-chloro-5-ethynylpyridine (2b), and the catalyst in a mixture
full matrix least-squares calculations based on F for all reflections
5
2.2 g
[48]. All non-hydrogen atoms were refined anisotropically. All
hydrogen atoms were included in the models in calculated positions
and were refined as constrained to bonding atoms.
(
2
of 70 mL diisopropylamine and 60 mL tetrahydrofuran were
used. After refluxing for 30 min, the reaction was complete.
CCDC 947220 (1a), 947221 (1b), 947222 (1c), 947223 (1d),
and 947224 (1e) contain the supplementary crystallographic data
for this article. These data can be obtained free of charge from the
Cambridge Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Purification by column chromatography (SiO
2
; n-hexane/ethyl
acetate; 1 : 1) yielded 1.5 g (67%) of a white solid, mp 230°C,
ꢀ
1
IR: ArCH 3094, CN 1676, CC 1584, 1546, CCl 1017 cm
;
1
4
H NMR (CDCl ): δ 8.56 (d, 2 H, J = 2.1 Hz, phenyl), 7.77 (dd,
H, J = 8.0Hz, J = 2.1 Hz, phenyl), 7.36 (d, 2 H, J = 8.0 Hz,
3
3
4
3
2
Acknowledgment. This work was performed within the Cluster
of Excellence “Structure Design of Novel High-Performance
Materials via Atomic Design and Defect Engineering (ADDE),”
which is financially supported by the European Union
1
3
phenyl); C NMR (CDCl
18.3, 89.0; MS: m/z 249 (M + H ); Anal. Calcd. for
C H N S (247.99): C, 57.86; H, 2.43; N, 11.25; Found: C,
3
): δ 152.1, 151.3, 140.9, 124.1,
+
1
1
8 22 4 2
5
7.99; H, 2.29; N, 11.16%.
,5′-Ethyn-1,2-diyl-bis-[2-(t-butylthio)pyrimidine] (1c).
.6 g (8.8 mmol) 2-(t-butylthio)-5-iodopyrimidine (4c), 1.8 g
(
European Regional Development Fund) and by the Ministry of
5
Science and Art of Saxony (SMWK).
2
(
9.1 mmol) 2-(t-butylthio)-5-ethynylpyrimidine (2c), and the
catalyst in a mixture of 60 mL diisopropylamine and 60 mL
tetrahydrofuran were used. After stirring for 90 min at room
temperature, the reaction was complete. Purification by column
REFERENCES AND NOTES
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J. Ed.; Springer: Berlin, Heidelberg, 2012, pp 219–246.
[2] Schirok, H.; Paulsen, H.; Kroh, W.; Chen, G.; Gao, P. Org
Process Res Dev 2010, 14, 168.
[
chromatography (SiO
2
; n-hexane/ethyl acetate; 1 : 20) yielded
2
1
.4 g (77%) of a white solid, mp 57°C, IR: ArCH 2963, CN
ꢀ
1
1
533, CH 1361 cm
; H NMR (CDCl ): δ 8.61 (s, 4 H,
3
13
phenyl), 1.63 (s, 18 H, CH3); C NMR (CDCl ): δ 172.7,
3
[3] Venturoni, F.; Nikbin, N.; Ley, S. V.; Baxendale, I. R. Org
+
1
58.3, 113.1, 88.8, 48.0, 29.9; MS: m/z 359 (M + H ); Anal.
Calcd. for C18 (358.13): C, 60.30; H, 6.18; N, 15.63;
S, 17.89; Found: C, 60.38; H, 6.32; N, 15.62; S, 17.90%.
Biomol Chem 2010, 8, 1798.
H
22
N
4
S
2
[4] Sillion, B. High Perform Polym 1999, 11, 417.
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
Ethynylene-Bridged Bisazines Featuring Various α-Substitution
[6] Curtis, N. F. In Comprehensive Coordination Chemistry II;
[27] Steed, J. W.; Atwood, J. L. Supramolecular Chemistry; Wiley:
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet