Heteroaryl functionalised diacetylenes: Preparation and solid-state reactivity

Article abstract of DOI:10.1039/a806078i

Diacetylenes are known to undergo solid-state topochemical polymerisation to give polydiacetylenes. The reactivity of the monomer is controlled by the arrangement of the molecules in the crystal lattice wherein certain parametric conditions must be met for 1,4-addition to proceed. In the present paper, we investigated the structure-reactivity relationship of a class of diacetylene monomers. Heteroaryl moieties such as thiophene, benzo[b]thiophene and quinoline as one or both directly bound side groups of a diacetylene backbone were used. Thus various symmetrical as well as unsymmetrical diacetylenes were prepared and characterised. The solid-state polymerisation behaviour of these diacetylenes was studied in the light of their single-crystal X-ray structure. It was found that in order to react in the solid state, the diacetylenes must have the required lattice parameters. However, even when the required lattice parameters are met, the diacetylene monomers do not necessarily undergo solid-state 1,4-addition polymerisation, implying the existence of further controlling factors to determine reactivity.

Full text of DOI:10.1039/a806078i

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Heteroaryl functionalised diacetylenes: preparation and solid-state
reactivity
Abhijit Sarkar† and Satya S. Talwar
Department of Chemistry, Indian Institute of Technology, Powai, Bombay 400 076, India
Received (in Cambridge) 3rd August 1998, Accepted 20th October 1998
Diacetylenes are known to undergo solid-state topochemical polymerisation to give polydiacetylenes. The reactivity
of the monomer is controlled by the arrangement of the molecules in the crystal lattice wherein certain parametric
conditions must be met for 1,4-addition to proceed. In the present paper, we investigated the structure–reactivity
relationship of a class of diacetylene monomers. Heteroaryl moieties such as thiophene, benzo[b]thiophene and
quinoline as one or both directly bound side groups of a diacetylene backbone were used. Thus various symmetrical
as well as unsymmetrical diacetylenes were prepared and characterised. The solid-state polymerisation behaviour of
these diacetylenes was studied in the light of their single-crystal X-ray structure. It was found that in order to react in
the solid state, the diacetylenes must have the required lattice parameters. However, even when the required lattice
parameters are met, the diacetylene monomers do not necessarily undergo solid-state 1,4-addition polymerisation,
implying the existence of further controlling factors to determine reactivity.
to extend further to provide longer effective conjugation length.
Introduction
The heteroaryl moiety, by virtue of its aromatic interactions
Substituted diacetylenes (DAs) undergo 1,4-addition reaction
with adjacent molecules, enhances the probability that the
in the solid state to give polydiacetylenes (PDAs).1 The reaction
can be initiated thermally, photochemically or by γ-irradiation.
The reaction is topochemically controlled wherein the packing
monomer would stack appropriately in the crystal for topo-
chemical polymerisation. As will be discussed in the following
sections, this strategy led us to obtain reactive as well as
arrangements of the molecules in the monomer crystal lattice
unreactive diacetylenes. Reactivity or lack of it has been exam-
must satisfy the requirements for solid-state polymerisation
ined in relation to molecular packing arrangements in the
(Scheme 1).2 The polymer PDA has a quasi-one-dimensional
structure with long effective conjugation length. This, in turn,
makes it a potential candidate for nonlinear optical material
diacetylene crystals using the crystal-packing information
obtained from X-ray single-crystal structure analysis of the
monomer diacetylenes.
with high and fast χ(3) response.3 The long conjugated backbone
also gives them excellent thermochromic properties.4 Con-
sequently, solid-state polymerisation is an area of research
interest for many scientists around the world. There have been a
lot of studies, both theoretical as well as experimental, to pre-
dict the solid-state polymerisation of diacetylenes.5–8 However,
the biggest hurdle in this area of research is to get monomers
which can be obtained in proper crystal lattice geometry suit-
able for polymerisation to PDAs. Numerous diacetylenes have
been prepared but only a few of them undergo 1,4-addition
reaction. Moreover, even when they do react, the polymer
formed may not exhibit the desired properties. For example, the
polymer may not be able to maintain crystallinity while trans-
forming from the monomer.
Since the packing arrangement of a diacetylene monomer is
Scheme 1 Topochemical solid-state polymerisation of diacetylene by
the determining factor for its solid-state reactivity, manipu-
lation of this to promote reactivity is most desired. In disubsti-
tuted diacetylenes, the only possible variations which can be
effected, as far as molecular engineering is concerned, are
manipulation of the side groups. We have been investigating the
aspect of structure–reactivity relationships of diacetylenes
toward solid-state polymerisation. One class of diacetylenes,
which we have been investigating, consists of aryl and hetero-
aryl moieties directly bound to the diacetylene backbone.9,10
The synthesis of diacetylene monomers with conjugated side
groups has attracted interest for a long time and a few reports
are also available in the literature.11–14 The design of such
diacetylenes has been based on the premise that the aromatic
side group will, in suitable cases, help the backbone conjugation
1,4-addition. When the monomer in the crystal has the appropriate
geometry, where the distance d and angle γ are about 5 Å and 45Њ, re-
spectively, it can be polymerised via topochemical 1,4-addition.
Results and discussion
The monomers were prepared following Scheme 2 and Scheme
3. The solid-state reactivity of all seven monomers synthesised
are summarised in Table 1. As can be seen, compound 4d shows
solid-state reactivity and undergoes 1,4-addition reaction to
give blue coloured PDA. The rest of the monomers do not
undergo 1,4-addition reaction in the solid state.
The X-ray diffraction studies of single crystals of five
diacetylenes, namely compounds 4a,15 4c,16 4d,17 6a18 and 7a19
have been carried out in order to probe the reactivity or un-
reactivity of the DAs towards topochemical 1,4-addition. The
results of single-crystal X-ray structure analysis are summar-
ised in Tables 2 and 3. While Table 2 lists the lattice parameters
† Present address: Institute for Chemical Reaction Science, Tohoku
University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. Ph./Fax:
ϩ81-22-217 5645. E-mail: asarkar@icrs.tohoku.ac.jp
J. Chem. Soc., Perkin Trans. 1, 1998, 4141–4146
4141

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Table 1 Reactivity of diacetylenes towards solid-state 1,4-addition
polymerisation
Table 2 Lattice parameters of diacetylene monomers
Diacetyl- Space
a
b
c
α
β
γ
Solid-state reactivity
ene
4a
4c
group
(in Å)
(in degrees)
Diacetylene
γ
UV
heat
P21/n
monoclinic
P21/n
monoclinic
P21/n
5.89
13.28
4.81 13.69 11.91 90
22.66 7.48 9.38 90
6.98 28.76 12.49 90
5.97 13.15 90 102.59 90
4a
4b
4c
4d
6a
7a
7b
×
×
×
᭺
×
×
×
×
×
×
᭺
×
×
×
×
×
×
᭺
×
×
×
3.96 14.12 90
92.11 90
95.34 90
4d
6a
7a
monoclinic
P21/n
90
90
90
90
orthorhombic
P21/n
orthorhomic
᭺: reactive, ×: unreactive.
Table 3 Distance d1 and angle γ of diacetylenesa
CH3
OH
CH3
H
C
C
C
Diacetylene
d1 (Å)
γ (degrees)
CH3
Ar-Br
4a
4c
4d
6a
7a
5.887
3.958
4.807
7.482
6.980
40.5
62.3
47.5
70.0
64.0
Ar
C
C
C
OH
(Ph3P)2PdCl2, CuCl, Et2NH
CH3
1a-d
2a-d
KOH, PhH,
reflux
a Variables d and γ are defined in Scheme 1.
1a-4a, Ar =
1b-4b, Ar =
S
S
Ar
C
C
H
3a-d
O2, CuCl
1c-4c, Ar =
1d-4d, Ar =
TMEDA, DMF
S
N
Ar
C
C
C
C
Ar
4a-d
Scheme 2 Synthetic route for symmetrical diacetylenes.
NaOH, H2O, Br2
Ar
C
C
Br
Ar
C
C
H
0–5 ˚C
5a,5d
3a,3d
CuCl, EtNH2, NH2OH•HCl,
EtOH, N2 atm.
5a
Ar
C
C
C
C
CH2OH
HC
C
CH2OH
6a
CuCl, EtNH2, NH2OH•HCl,
EtOH, N2 atm.
Fig. 1 Unit-cell packing diagram of compound 4a.
3a,3b
Ar
C
C
C
C
Ar'
Fig. 1 shows the unit-cell packing diagram of compound 4a.
In this crystal, both the thiophene rings are disordered. Thus
the position of sulfur and carbon atoms in thiophene rings,
adjacent to the diacetylenic backbone, are interchangeable but
with unequal occupations. The thiophene rings are planar and
the dihedral angle between them is 65.6Њ. The diacetylene
chains are inclined to the shortest axis, i.e. the a-axis, by 40.5Њ
and the perpendicular distance between the adjacent chains
is 3.823 Å, as against the respective values of 45Њ and 3.4 <
S1 < 4.0 Å, required for solid-state polymerisation.2 Thus, it is
surprising that compound 4a is unreactive even though it has
favourable packing arrangements. The disordered structure of
compound 4a, may partially explain its non-reactivity in the
solid state.
5d
7a,7b
Ar' =
N
Scheme 3 Synthetic route for unsymmetrical diacetylenes.
for the monomers, Table 3 summarises the packing parameters
(d1 and γ) relevant for topochemical 1,4-addition polymeris-
ation.‡ Most of the monomers adhere to the established
principles of topochemical 1,4-addition with the exception of
compound 4a.
Preliminary X-ray diffraction data of compound 4b indicate
that this diacetylene also has a disordered structure in its crystal
state.20
It is possible that each of the diacetylenes 4a and 4b exists in
a more ordered phase at a temperature below ambient, which
could be a reactive phase. In order to confirm this view,
low-temperature differential scanning calorimetry (DSC) was
‡ Full crystallographic details, excluding structure factor tables, have
been deposited at the Cambridge Crystallographic Data Centre
(CCDC). For details of the deposition scheme, see ‘Instructions for
Authors’, J. Chem. Soc., Perkin Trans. 1, available via the RSC Web
page (http://www.rsc.org/authors). Any request to the CCDC for this
material should quote the full literature citation and the reference
number 207/271.
4142
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Fig. 2 DSC of compound 4a at low temperature (0–20 ЊC).
Fig. 4 Stacking of compound 4d molecules along b-axis.
Fig. 3 Unit-cell packing diagram of compound 7a down the a-axis.
carried out. As a typical case, the result for 4a is shown in
Fig. 2. Endotherms were observed at 10 ЊC for compound 4a
and at 6.5 ЊC for compound 4b with ∆H of 0.037 kcal molϪ1
§
and 0.014 kcal molϪ1, respectively. Following this result, solid-
state polymerisation of compounds 4a and 4b was attempted at
temperatures below Ϫ20 ЊC using high-power UV radiation.
Even after several hours of exposure, neither of the two mono-
mers showed any reactivity. Therefore, this suggests that even
though the diacetylene crystals were in more ordered forms at
the lower temperatures, enhanced order is not enough to induce
reactivity. In other words, the disordered structure of com-
pounds 4a and 4b is just one factor, among others, responsible
for their lack of solid-state reactivity.
The crystal structure of compound 7a also revealed that it has
a disordered structure (Fig. 3). In the thiophene ring within
each molecule of compound 7a, the position of the sulfur atom
and the carbon atom flanking the diacetylenic backbone are
interchangeable. Moreover, the stacking of the molecules of
compound 7a is not parallel. These factors make this monomer
unreactive towards solid-state polymerisation despite a short
C(sp)–C(sp) distance of adjacent molecules. However, it may be
noted that polymerisation has been observed in diacetylene
crystals in which diacetylene molecules are packed in non-
parallel stacks.21
Fig. 5 Plot showing monomer-packing requirements for solid-state
1,4-addition. To be reactive, the diacetylene (DA) should fall inside the
contour formed by the solid curve and the dotted curve. Experimental
data obtained in the present study for reactive DAs (᭺) and unreactive
DAs (×) are plotted in the graph.
the same as the ideal values proposed for topochemical 1,4-
addition. The percentage polymer conversion, however, was low
(25%). The χ(3)-value for this polymer has been estimated to be
in the order of 10Ϫ11 esu by third-harmonic generation meas-
urement.10 The PDA obtained from compound 4d is blue in
colour and shows a high absorption λmax of 715 nm. This is in
line with our postulation that directly bound heteroaryl groups
contribute favourably towards the conjugation length of the
PDA chain.
The topochemical reaction criteria can be expressed by draw-
ing contours for 1,4-carbon separation of 4.0 Å and an arbitrar-
ily chosen r.m.s. displacement of 1.0 Å in the space with
coordinates equal to the separation of the centres of gravity
between the axes of the diacetylene units and the stack (Fig. 5).6
Not all values of d1 and γ are allowed since the diacetylene units
cannot approach closer than twice the van der Waals radii of
the acetylenic carbons. This limit is shown by the solid-line
curve in Fig. 5. Values of d1 and γ obtained from X-ray struc-
ture analysis of the diacetylenes reported here are plotted in
Fig. 5. It is observed that, except for compounds 4a and 4d,
all other diacetylenes tested do not fulfil the requirements for
topochemical reactivity. It is noteworthy that even compound
4a, falling within the contour, does not show topochemical
reactivity.
For crystals 4c and 6a, the distance between adjacent mole-
cules in a stack as well as the angle between the molecular axis
and the stack axis are not suitable for 1,4-addition reaction to
occur.
Diacetylene 4d undergoes topochemical 1,4-addition.9 The
crystal structure of this compound reveals that the molecules
have parallel stacking along the b-axis (Fig. 4). The quinoline
rings are almost parallel to each other within a molecule as well
as among adjacent molecules in the stack. The d1- and γ-values
are 4.8 Å and 47.5Њ, respectively. These values are almost
§ 1 cal = 4.184 J.
J. Chem. Soc., Perkin Trans. 1, 1998, 4141–4146
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There are reports on diacetylenes with aromatic side groups
which are unreactive towards solid-state polymerisation. The
crystal structures of these diacetylenes reveal that they do not
fulfil the packing requirements for 1,4-addition reaction.22,23 It
has been a general contention that a methylene group next to
the diacetylene backbone acts as a mechanical tuner and eases
out the strain developed in the crystal during polymerisation
and facilitates higher polymer conversion.24 A recent study
reported good topochemical reactivity of a diacetylene contain-
ing a tetrathiafulvalene side group attached to the backbone
through an alkyl chain.25 None of the diacetylenes reported in
this study, except for compound 6a, possesses such a methylene
group. This could be a major contributing factor towards non-
reactivity of the monomers.
CuI (0.05 g) was added dry, distilled diethylamine (90 ml)
followed by 2-methylbut-3-yn-2-ol (4.13 g, 0.049 mol) and
2-bromothiophene 1a (8.1 g, 0.049 mol). The reaction mixture
was stirred for 8 h at rt under dry N2. Diethylamine was
removed under reduced pressure, water was added to the reac-
tion mixture, and then it was extracted with diethyl ether. After
drying of the extract over MgSO4 and removal of ether, a
brown slurry was obtained, which was chromatographed
through a silica gel column using petroleum spirit–ethyl acetate
(80:20) as eluent. Yellowish solid alcohol 2a was obtained,
which was further purified by recrystallisation from petroleum
spirit to afford needles (80%), mp 54 ЊC; νmax(KBr)/cmϪ1 3300
᎐
(OH), 3030 (arom. C᎐H), 2960 (aliph. C᎐H), 2200 (C᎐C) and
᎐
1
1370 and 1380 (gem dimethyl); H NMR (60 MHz; CDCl3)
Some of the monomers were used to determine their
third-order nonlinear properties by the Z-scan technique.26 The
second molecular hyperpolarisability γ (Ϫω, ω, ω, Ϫω) was
found to be large (0.66 to 11.20 × 10Ϫ32 esu) for these small
molecules. Thus, the study indicates that the symmetrical
substitution with conjugated heterocyclic end-groups is the
contributing factor for enhancement of their γ-values.
δH 1.60 (s, 6H), 2.20 (s, 1H), 6.94–6.98 (dd, 1H), 7.18 (d, 1H)
and 7.24 (d, 1H); 13C NMR (100 MHz; CDCl3) δC 31.20, 64.98,
78.02, 81.42, 121.91, 125.43, 129.99 and 134.02 (Found: C, 64.9;
H, 6.5; S, 19.25. Calc. for C9H10OS: C, 65.02; H, 6.71; S,
19.29%).
Preparation of 2-methyl-4-(3Ј-thienyl)but-3-yn-2-ol 2b
The procedure followed was similar to that given for isomer
2a above. However, the time required for completion of the
reaction was much longer (12 h) in the present case. After
work-up, the crude product was recrystallised from methanol to
give pure title alcohol 2b as crystals (81%), mp 115–116 ЊC;
νmax(KBr)/cmϪ1 3300 (OH), 3030 (arom. C᎐H), 2965 (aliph.
Conclusions
In conclusion, we have successfully synthesised a series of
diacetylenes which are functionalised with heteroaryl moieties.
The heteroaryl side groups were linked directly to the diacetyl-
ene backbone in order to get maximum π-conjugation effect.
These DAs were prepared with the aim of probing the structure–
solid-state reactivity relationship with respect to 1,4-addition.
We have based our investigation on the single-crystal X-ray
structure of the monomers because the above polymerisation
reaction is highly dependent on the molecular-packing arrange-
ment in monomer crystals. Our investigation has revealed that
although the criteria proposed for topochemical 1,4-addition
are necessary, they are not sufficient for reactivity. Other fac-
tors, like disordered crystal structure, may also play a role in
controlling reactivity. The diacetylene 4d, on the other hand,
reacts to give polydiacetylene with high effective conjugation
length as expected from such a type of PDA.
1
᎐
C᎐H), 2215 (C᎐C) and 1370 and 1380 (gem dimethyl); H
᎐
NMR (60 MHz; CDCl3) δH 1.54 (s, 6H), 2.15 (s, 1H) and 7.18–
7.34 (m, 3H); 13C NMR (100 MHz; CDCl3) δC 31.41, 65.20,
79.46, 80.15, 121.10, 125.84, 130.19 and 134.02 (Found: C, 65.0;
H, 6.5; S, 19.1. Calc. for C9H10OS: C, 65.02; H, 6.71; S, 19.29%).
Preparation of 4-(3Ј-benzo[b]thienyl)-2-methylbut-3-yn-2-ol 2c
The procedure followed was similar to that given for compound
2a above. The reaction was complete in 6 h. After work-up,
column chromatography and crystallisation, pure title alcohol
2c was obtained as needles (50%), mp 71 ЊC; νmax(KBr)/cmϪ1
᎐
3300 (OH), 3030 (arom. C᎐H), 2980 (aliph. C᎐H), 2210 (C᎐C),
᎐
1640 (arom. C᎐H) and 1370 and 1380 (gem dimethyl); 1H NMR
(60 MHz; CDCl3) δH 1.65 (s, 6H), 2.81 (s, 1H) and 7.18–8.00
(m, 5H); 13C NMR (100 MHz; CDCl3) δC 31.52, 65.11, 76.98,
78.44, 117.00, 127.02, 127.31, 128.21, 129.45, 130.48, 139.73
and 143.42 (Found: C, 72.0; H, 5.5; S, 14.6. Calc. for C13H12OS:
C, 72.19; H, 5.59; S, 14.82%).
Experimental
Solvents and reagents used in this work were purified according
to standard literature techniques and stored under nitrogen.
Solvents were freshly distilled prior to use. Commercially avail-
able 2-bromothiophene 1a, 3-bromothiophene 1b and 3-bromo-
quinoline 1c (Aldrich) were used as obtained. 3-Bromobenzo-
[b]thiophene 1c was prepared from benzo[b]thiophene accord-
ing to the literature procedure.27 KCl and CuI were used as
obtained. 2-Methylbut-3-yn-2-ol (Fluka or Aldrich) and
diethylamine were distilled before use. Cuprous [copper()]
chloride was purified before use. Petroleum spirit refers to the
fraction with distillation range 40–60 ЊC.
Preparation of 2-methyl-4-(3Ј-quinolyl)but-3-yn-2-ol 2d
The procedure followed was similar to that given for compound
2a above. After work-up, column chromatography and crystal-
lisation, pure title alcohol 2d was obtained as needles (60%), mp
115–116 ЊC; νmax(KBr)/cmϪ1 3250 (OH), 3030 (arom. C᎐H),
᎐
2965 (aliph. C᎐H), 2215 (C᎐C) and 1370 and 1380 (gem di-
᎐
1
methyl); H NMR (60 MHz; CDCl3) δH 1.62 (s, 6H), 2.54
(s, 1H), 7.58–8.24 (m, 4H), 8.32–8.41 (d, 1H) and 9.0 (br s, 1H);
13C NMR (100 MHz; CDCl3) δC 31.39, 65.27, 78.21, 85.25,
116.05, 127.01, 127.63, 127.66, 129.04, 130.81, 140.44, 146.52
and 152.22 (Found: C, 79.3; H, 6.1; S, 6.5. Calc. for C14H13NO:
C, 79.59; H, 6.20; N, 6.63%).
Purification of the synthesised compounds was by crystallis-
ation from suitable solvents. Column chromatography was done
using 100–200 mesh silica gel. TLC was used to monitor the
reactions. Mps were determined by the capillary method using
a Veeco melting point apparatus model MP-5 and are uncor-
rected. IR spectra were taken in a Perkin-Elmer 681 IR spectro-
photometer. Proton NMR spectra were recorded on either
a 60 MHz Hitachi-600 of a 400 MHz Varian VXR-400
spectrometer. 13C NMR spectra were recorded on a 400 MHz
Varian VXR-400 spectrometer. Elemental analysis was done
using a Carlo Erba Model 1106 elemental analyser. The single-
crystal X-ray diffraction and analysis were carried out on a
Philips X-ray diffractometer PW 1140.
Preparation of 2-thienylacetylene 3a
A solution of alcohol 2a (3 g, 0.018 mol) in dry benzene (30 ml)
containing potassium hydroxide (1.2 g) and methanol (5 ml)
was refluxed in a flask equipped with a Dean–Stark trap. The
reaction was found to be complete after 9 h. The reaction prod-
uct was carefully distilled under reduced pressure to obtain pure
title compound 3a (90%), bp 129–131 ЊC (lit.,28 bp20 54–60 ЊC).
Preparation of 2-methyl-4-(2Ј-thienyl)but-3-yn-2-ol 2a
Preparation of 3-thienylacetylene 3b
To bis(triphenylphosphine)palladium() chloride (0.175 g) and
The procedure followed was similar to that given for isomer 3a.
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The refluxing was continued for 14 h in order to let the reaction
go to completion. Yield 81%, bp 129 ЊC (lit.,29 bp15 48–50 ЊC).
in this case was (3-benzo[b]thiophenyl)acetylene 3c. Yield of
product was 42%, mp 165 ЊC; νmax(KBr)/cmϪ1 2120 (C᎐C) and
᎐
᎐
1
1600 (arom. C᎐C); H NMR (400 MHz; CDCl3) δH 7.01 (dd,
2H), 7.07 (dd, 2H), 7.51 (d, 2H), 7.54 (d, 2H) and 7.66 (s, 2H);
13C NMR (100 NHz; CDCl3) δC 75.94, 76.31, 117.00, 127.22,
127.51, 128.43, 129.66, 130.67, 139.86 and 143.55 (Found: C,
76.3; H, 3.3; S, 20.0. Calc. for C20H10S2: C, 76.40; H, 3.21; S,
20.40%).
Preparation of (3-benzo[b]thienyl)acetylene 3c
The procedure followed was similar to that given for compound
3a. The reaction took only 3 h to finish. Pure title compound 3c
was obtained as a yellowish liquid (55%), bp 146 ЊC; νmax(KBr)/
cmϪ1 3300 (C᎐C᎐H), 2100 (C᎐C) and 1600 (arom. C᎐C); H
1
᎐
᎐
᎐
᎐
NMR (60 MHz; CDCl3) δH 3.6 (s, 1H) and 7.18–8.13 (m, 5H);
13C NMR (100 MHz; CDCl3) δC 77.95, 78.92, 117.25, 127.09,
127.42, 128.39, 129.55, 130.57, 139.82 and 143.51 (Found: C,
75.5; H, 3.75; S, 20.0. Calc. for C10H6S2: C, 75.91; H, 3.82; S,
20.27).
Preparation of 1,4-bis(3-quinolyl)buta-1,3-diyne 4d
Compound 4d was synthesised using the same method as was
used for the synthesis of compound 4a. The starting material in
this case was 3-quinolylacetylene 3d. Yield of product was 42%,
mp 165 ЊC; νmax(KBr)/cmϪ1 2120 (C᎐C) and 1600 (arom.
᎐
᎐
C᎐C); 1H NMR (400 MHz; CDCl3) δH 7.60 (dd, 2H), 7.75 (dd,
Preparation of 3-quinolylacetylene 3d
2H), 7.80 (dd, 2H), 8.10 (d, 2H), 8.31 (s, 2H) and 8.95 (s, 2H);
13C NMR (100 MHz; CDCl3) δC 78.22, 80.01, 116.95, 127.41,
127.53, 127.62, 129.00, 130.85, 140.50, 146.67 and 152.35
(Found: C, 87.4; H, 3.3; N, 9.3. Calc. for C22H12N2: C, 87.10;
H, 3.57; N, 9.23%).
In a round-bottom flask, fitted with a magnetic stirrer was
placed a mixture of 2-methyl-4-(3Ј-quinolyl)but-3-yn-2-ol 2d
(18 g, 0.085 mol) in benzene (400 ml). A mixture of powdered
KOH (3 g) and 18-crown-6 ether (0.5 g) in benzene (50 ml) was
added to the stirred mixture. The mixture was stirred for 24 h at
rt until the reaction was complete. The mixture was filtered
and the filtrate was concentrated under reduced pressure. Pure
compound 3d was obtained by filtration column chrom-
atography with 4:1 petroleum spirit–ethyl acetate. Shining crys-
tals of compound 3d were obtained by recrystallisation from
Preparation of 1-bromo-2-(2Ј-thienyl)ethyne 5a
Bromine (320 mg, 0.004 mol) was added to aq. KOH (0.01 mol
in 10 ml) stirred at 0–5 ЊC. 2-Thienylacetylene 3a as a solution
in 1,4-dioxane (108 mg, 0.001 mol/20 ml) was added dropwise
to the above mixture over a period of 15 min. The reaction
mixture was stirred for another 15 min without further cooling
and poured into 50 ml of ice-cold water. The product was
extracted with diethyl ether. Upon drying over MgSO4 and
petroleum spirit (84%), mp 80 ЊC [lit.,30 mp 81 ЊC]; νmax(KBr)/
1
cmϪ1 3300 (C᎐C᎐H) and 2110 (C᎐C), 1600 (arom. C᎐C); H
᎐
᎐
᎐
᎐
NMR (60 MHz; CDCl3) δH 3.55 (s, 1H), 7.49–8.20 (m, 4H),
8.31–8.41 (d, 1H) and 9.0 (br s, 1H); 13C NMR (100 MHz;
CDCl3) δC 81.01, 85.33, 116.95, 127.64, 127.99, 128.10, 129.50,
131.12, 140.68, 146.75 and 152.25 (Found: C, 86.2; H, 4.6; N,
9.0. Calc. for C11H7N: C, 86.25; H, 4.61; N, 9.14%).
removal of solvent, 5a was obtained as a yellow oil (82%), bp
1
(at 5 mmHg) 40 ЊC; νmax(KBr)/cmϪ1 2190 (C᎐C); H NMR (60
᎐
᎐
MHz; CDCl3) δH 6.80–7.50 (m, 3H); 13C NMR (100 MHz;
CDCl3) δC 80.92, 81.83, 121.17, 125.92, 130.30 and 132.22
(Found: C, 38.45; H, 1.58; S, 17.0. Calc. for C6H3BrS: C, 38.53;
H, 1.62; S, 17.14%).
Preparation of 1,4-bis(2-thienyl)buta-1,3-diyne 4a
To a magnetically stirred suspension of CuCl (190 mg) in DME
(10 ml) was added TMEDA (0.5 ml). After 10 min at rt the
mixture was treated with 2-thienylacetylene 3a (1 g, 0.009 mol)
and the solution was stirred while O2 was bubbled through
it. The colour of the reaction mixture turned from blue to
yellowish green. The reaction was found to be complete after
2 h. The mixture was poured into water and was extracted with
ether. The ether layer was dried over MgSO4 and then concen-
trated under reduced pressure to obtain a crude product as a
yellowish solid. This was passed through a silica gel column,
using petroleum spirit as eluent. Diyne 4a was obtained as a
solid, which was further purified by crystallisation to obtain
Preparation of 1-bromo-2-(3Ј-quinolyl)ethyne 5d
Bromine (320 mg, 0.004 mol) was added to aq. KOH (0.01 mol
in 10 ml) stirred at 0–5 ЊC. 3-Quinolylacetylene 3d as a solution
in 1,4-dioxane (153 mg, 0.001 mol/20 ml) was added dropwise
to the above mixture over a period of 15 min. The reaction
mixture was stirred for another 15 min without further cooling.
Then the reaction mixture was poured into 50 ml of ice-cold
water, when a solid precipitated out. The precipitate was filtered
off, dried, and recrystallised from methanol (82%), mp 118–
119 ЊC; νmax(KBr)/cmϪ1 2200 (C᎐C); 1H NMR (60 MHz;
᎐
᎐
CDCl3) δH 7.50–9.00 (m, 6H); 13C NMR (100 MHz; CDCl3) δC
needles (40%), mp 89 ЊC; νmax(KBr)/cmϪ1 2130 (C᎐C) and 1620
᎐
᎐
(arom. C᎐C); 1H NMR (400 MHz; CDCl3) δH 7.02 (d, 2H), 7.34
81.01, 85.33, 116.95, 127.64, 127.99, 128.10, 129.50, 131.12,
140.68, 146.75 and 152.25 (Found: C, 57.5; H, 2.6; N, 5.9. Calc.
for C11H6BrN: C, 56.92; H, 2.60; N, 6.03%).
(dd, 2H) and 7.37 (d, 2H); 13C NMR (100 MHz; CDCl3)
δC 76.74, 77.86, 121.93, 127.30, 129.02 and 134.49 (Found: C,
67.16; H, 2.8; S, 29.6. Calc. for C12H6S2: C, 67.76; H, 2.82; S,
29.92%).
Preparation of 1-(2Ј-thienyl)penta-1,3-diyn-5-ol 6a
A catalytic slurry of CuCl (100 mg), 70% aq. ethylamine (30
ml), NH2OHؒHCl (300 mg in 20 ml of water) and ethanol (60
ml) was prepared in a three-neck flask under argon. Propargyl
alcohol (prop-2-ynol) (1 g, 0.01 mol) was added dropwise to the
above slurry. The colour of the solution turned greenish yellow.
The flask was maintained at a temperature of 40–45 ЊC and a
solution of 1-bromo-2-(2Ј-thienyl)ethyne 5a in ethanol (1.03 g,
0.0068 mol/40 ml) was added dropwise to the above mixture.
The reaction mixture was stirred for another 3 h until comple-
tion of the reaction. The mixture was then poured into vigor-
ously stirred ice-cold water (150 ml). A solid slowly precipitated
out, and was filtered off, and extracted with ether. The ether
layer was washed with saturated aq. ammonium chloride. The
organic layer was dried over anhydrous MgSO4, filtered and
concentrated. After column chromatography through a silica
gel column, pure diynol 6a was obtained as a crystalline solid
Preparation of 1,4-bis(3-thienyl)buta-1,3-diyne 4b
Compound 4b was synthesised using the same Glasser’s coup-
ling method as was used for the synthesis of isomer 4b. The
starting material in this case was 3-thienylacetylene 3b. Yield of
diyne 4b was 40%, mp 111 ЊC; νmax(KBr)/cmϪ1 2140 (C᎐C) and
᎐
᎐
1
1600 (arom. C᎐C); H NMR (400 MHz; CDCl3) δH 7.18 (d,
2H), 7.30 (dd, 2H) and 7.60 (d, 2H); 13C NMR (100 MHz;
CDCl3) δC 73.52, 76.58, 120.90, 125.84, 130.19 and 131.28
(Found: C, 67.11; H, 2.82; S, 29.63. Calc. for C12H6S2: C, 67.76;
H, 2.82; S, 29.92%).
Preparation of 1,4-bis(3-benzo[b]thienyl)buta-1,3-diyne 4c
Compound 4c was synthesised using the same method as was
used for the synthesis of compound 4a. The starting material
J. Chem. Soc., Perkin Trans. 1, 1998, 4141–4146
4145

View Article Online
(45%), mp 81 ЊC; νmax(KBr)/cmϪ1 3400 (OH), 3000 (arom.
fractometer with Mo-Kα radiation. Data reduction and appli-
cation of Lorentz and polarisation corrections were carried out
using the Enraf-Nonius Structure Determination Package.
1
᎐
C᎐H), 2962 (aliph. C᎐H) and 2150 (C᎐C); H NMR (400 MHz;
᎐
CDCl3) δH 1.76 (br s, 1H), 4.42 (s, 2H), 6.98 (dd, 1H), 7.31 (d,
1H) and 7.33 (d, 2H); 13C NMR (100 MHz; CDCl3) δC 66.25,
70.34, 71.70, 80.12, 82.58, 121.64, 127.10, 128.80 and 134.75
(Found: C, 66.3; H, 3.7; S, 19.6. Calc. for C9H6OS: C, 66.64; H,
3.73; S, 19.77%).
Acknowledgements
We gratefully acknowledge the research fellowship awarded
to A. S. by the Council for Scientific and Industrial Research,
New Delhi.
Preparation of 1-(3Ј-quinolyl)-4-(2Ј-thienyl)buta-1,3-diyne 7a
To a suspension of CuCl (12 mg), ethylamine (1 ml) and
hydroxylamine hydrochloride (100 mg) in ethanol (5 ml) was
added dropwise a solution of 2-thienylacetylene 3a (250 mg,
0.023 mol) in N,N-dimethylacetamide (DMA) (11 ml). After-
wards, (bromoethynyl)quinoline 5d (300 mg, 0.013 mol) as a
solution in 71 ml of DMA was added at 30 ЊC. The reaction was
carried out under nitrogen. After being stirred for 1.5 h the
mixture was poured into 50 ml of ice-cold water; the precipitate
was filtered off, and recrystallised from methanol. The pure
diyne 7a was obtained as needles (60%), mp 126 ЊC; νmax(KBr)/
References
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cmϪ1 3100 (arom. C᎐H), 2133 (C᎐C), 1640, 1600 and 1580
᎐
᎐
1
(arom. C᎐C); H NMR (400 MHz; CDCl3) δH 7.02 (dd, 1H),
7.36 (d, 1H), 7.39 (d, 1H), 7.60 (dd, 1H), 7.75 (dd, 1H), 7.80
(d, 1H), 8.10 (d, 1H), 8.30 (s, 1H) and 8.95 (s, 1H); 13C NMR
(100 MHz; CDCl3) δC 75.90, 77.03, 77.62, 80.80, 116.59, 121.10,
125.44, 127.01, 127.45, 127.66, 129.04, 129.99, 130.81, 132.71,
140.54, 146.51 and 153.12 (Found: C, 82.2; H, 2.8; N, 4.4; S, 9.9.
Calc. for C22H9NS: C, 82.73; H, 2.84; N, 4.39; S, 10.04%).
Preparation of 1-(3Ј-quinolyl)-4-(3Ј-thienyl)buta-1,3-diyne 7b
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The preparation of compound 7b was achieved using a similar
method to that for isomer 7a. The starting materials used were
3-thienylacetylene 3b and (bromoethynyl)quinoline 5d. Pure
compound 7b was obtained as needles (48%), mp 133 ЊC;
νmax(KBr)/cmϪ1 3100 (arom. C᎐H), 2133 (C᎐C), 1640, 1600 and
᎐
᎐
1
1580 (arom. C᎐C); H NMR (400 MHz; CDCl3) δH 7.21 (d,
1H), 7.30 (d, 1H), 7.61 (dd, 1H), 7.66 (dd, 1H), 7.75 (dd, 1H),
7.80 (dd, 1H), 8.10 (d, 1H), 8.30 (s, 1H) and 8.90 (s, 1H); 13C
NMR (100 MHz; CDCl3) δC 73.91, 77.16, 78.08, 78.62, 116.18,
120.54, 125.82, 127.01, 127.45, 127.66, 129.04, 129.99, 130.81,
134.02, 140.44, 146.51 and 153.01 (Found: C, 82.7; H, 2.8; N,
4.2; S, 9.9. Calc. for C22H9NS: C, 82.73; H, 2.84; N, 4.39; S,
10.04%).
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Solid-state polymerisation
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Polymerisation behaviour of the DA monomers was examined
using UV and γ-rays as well as anealing. Freshly prepared
monomer crystals were used for exposure to the above stimuli.
Only compound 4d turned blue by all three modes of stimuli,
indicating that it is solid-state reactive. The rest of the mono-
mers turned from colourless to brown, suggesting that 1,4-
addition is not occurring for these DAs. γ-Radiation was used
to polymerise compound 4d in bulk. The percentage conversion
of the reactive monomer to polymer was obtained by extracting
out the unchanged monomer after solid-state polymerisation.
The weight of the monomer before polymerisation and the
weight of the extracted polymer were used to calculate the
percentage polymer conversion.
26 A. V. V. Nampoothiri, P. N. Puntambeker, B. P. Singh, R. Sachdeva,
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Single crystal X-ray data
Single crystals of 4a, 4c, 4d, 6a and 7a, that were suitable for X-
ray crystallographic analyses, were obtained by slow evapor-
ation from suitable organic solvents. The structure solution and
refinement details for the compounds have been published
elsewhere,16–19 and so will only be briefly discussed here. Lattice
parameters at 25 ЊC or 27 ЊC were determined by least-squares
fit to the setting parameters of 25 independent reflections. Data
were measured on an Enraf-Nonius CAD4F four-circle dif-
28 T. B. Patrick and J. C. Honeggar, J. Org. Chem., 1974, 39, 3791.
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Paper 8/06078I
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J. Chem. Soc., Perkin Trans. 1, 1998, 4141–4146