1,2,3-Thiadiazoles with unsaturated side chains; synthesis, polymerization, and photocrosslinking

Article abstract of DOI:10.1055/s-0029-1216879

1,2,3-Thiadiazoles with polymerizable functionalities in the 4-position were synthesized as potential negative photoresists. The polymerization to soluble, film-forming materials must leave the heterocyclic rings intact, because they are needed for photocrosslinking reactions to give insoluble materials. 1,2,3-Thiadiazoles 1 cycloeliminate N₂ on irradiation. The resulting 1,3-diradicals 2 have various options for stabilization processes leading to alkynes 3 or to higher heterocycles 5-12. The generation of atomic sulfur and its involvement in these subsequent reactions must be avoided. Therefore, systems like model compound 1a, in which the 1,3-diradicals form 2-methylene-1,3-dithioles (dithiafulvenes) 9 were selected here. Optimization gave ultimately two materials for application as photoresists. Monomer 1c could be polymerized in the presence of boron trifluoride to soluble 1c′, which on irradiation formed 1c″ as a cross-linked insoluble polymer. Furthermore, thiadiazole 1f was attached to polystyrene 26. The resulting soluble polymer 1i′ yielded the insoluble material 1i″ on irradiation. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0029-1216879

PAPER
2539
1,2,3-Thiadiazoles with Unsaturated Side Chains; Synthesis, Polymerization,
and Photocrosslinking
Photocrosslinking
w
ith
o
1,2,3-Thiad
u
iazole sa Al-Smadi,*a,b Norbert Hanold,b Helga Kalbitz,b Herbert Meier*b
a
Department of Applied Chemical Sciences, Jordan University of Science and Technology, Irbid, Jordan
E-mail: mariam10@just.edu.jo
b
Institute of Organic Chemistry, University of Mainz, Duesbergweg 10-14, 55099 Mainz, Germany
Fax +49(6131)3925396; E-mail: hmeier@mail.uni-mainz.de
Received 23 February 2009; revised 22 April 2009
with unsaturated side chains14–24 and their polymers have
been studied, but the non-uniform dimerization of 2, in
particular the generation of ‘vagabonding’ sulfur atoms in
primary or secondary processes has proved to be a draw-
Abstract: 1,2,3-Thiadiazoles with polymerizable functionalities in
the 4-position were synthesized as potential negative photoresists.
The polymerization to soluble, film-forming materials must leave
the heterocyclic rings intact, because they are needed for photo-
crosslinking reactions to give insoluble materials. 1,2,3-Thiadiaz- back for the fabrication of negative photoresists.20,21
oles 1 cycloeliminate N2 on irradiation. The resulting 1,3-diradicals
2 have various options for stabilization processes leading to alkynes
3 or to higher heterocycles 5–12. The generation of atomic sulfur
have a much lower tendency for secondary sulfur extru-
and its involvement in these subsequent reactions must be avoided.
Therefore, systems like model compound 1a, in which the 1,3-
diradicals form 2-methylene-1,3-dithioles (dithiafulvenes) 9 were
4-Phenyl-1,2,3-thiadiazole (1a) fulfills the above-
Therefore, we attempted now to find systems with fairly
clean photoprocesses 1 to 9. The dimers 9, dithiafulvenes,
sion than other dimers.
selected here. Optimization gave ultimately two materials for appli-
cation as photoresists. Monomer 1c could be polymerized in the
presence of boron trifluoride to soluble 1c¢, which on irradiation
1,3-diradical 2a is formed, in which the hydrogen atom
formed 1c¢¢ as a cross-linked insoluble polymer. Furthermore, thia-
diazole 1f was attached to polystyrene 26. The resulting soluble
polymer 1i¢ yielded the insoluble material 1i¢¢ on irradiation.
mentioned preconditions as a model compound in a nearly
perfect manner. After light-induced nitrogen extrusion, a
has a high migration ability 2a→5a (Scheme 2). The gen-
erated thioketene 5a is involved in the cycloaddition of 2a
with 5a to give (Z/E)-9a. The Z/E ratio is 10:1, when the
irradiation of 1a is performed in benzene with Vycor-
filtered light (lirr 230 nm). Apart from 9a some polymers
are formed in the photocleavage of 1a, but the other pos-
sible reaction routes leading to 3, 6, 7, 8, 10, 11, and 12
can be excluded.5,25
Key words: cyclodimerization, cycloelimination, heterocycles,
photochemistry, photoresists
1,2,3-Thiadiazoles 1 represent a prominent class of het-
erocycles that have attracted attention for their interesting
pharmacological and biological properties, but also be-
cause they can be used for the preparation of various sul-
fur-containing ring systems.1 Thermal or photochemical
extrusion of nitrogen generates 1,3-diradicals 2, which
can rearrange to thioketenes 5 or eliminate sulfur to yield
alkynes 3 (Scheme 1). Thiirenes 4 are possible intermedi-
ates.1 Apart from these monomolecular reactions, there
are many dimerizations of 2/5 to heterocycles 6–12 with
1–4 sulfur atoms. Scheme 1 gives a survey of the forma-
tion of these heterocycles from four- to seven-membered
rings.2–12 (The examples given in refs. 2–12 are typically
early established reaction examples.) Stereoisomers of 6–
9 and regioisomers of 10–12 can be generated when the
1,2,3-thiadiazoles 1 have different substituents in the 4- or
5-positions. 1,2,3-Thiadiazoles with other substituents
than alkyl or aryl groups have many additional routes for
the stabilization of the initially formed 1,3-diradicals.13
Our task was then to synthesize 1,2,3-thiadiazoles with 4-
aryl substituents, which permit cationic polymerization.
In order to attach an olefinic chain to the 4-phenyl substit-
uent in 1a, we prepared first 4-(allyloxy)acetophenone
(15) by the almost quantitative alkylation of 4-hydroxy-
acetophenone (13) with allyl bromide (14) (Scheme 3).26
4-Toluenesulfonyl hydrazide (16) yielded hydrazone 17,
which was subjected to Hurd–Mori reaction27 with thionyl
chloride to give 4-[4-(allyloxy)phenyl]-1,2,3-thiadiazole
(1b). Finally a double bond shift to give (Z)- and (E)-4-[4-
(prop-1-enyloxy)phenyl]-1,2,3-thiadiazole
[(E/Z)-1c]
could be induced by the Wilkinson catalyst chloro-
tris(triphenylphosphine)rhodium in the presence of 1,4-
diazabicyclo[2.2.2]octane.
Thiadiazole 1d (Scheme 4), which contains an oxirane
ring, represents another polymerizable monomer. It could
be obtained by oxidation of 1b with 3-chloroperbenzoic
acid (18). However, the yield of the oxidation was moder-
ate, because the thiadiazole ring itself was sensitive to ox-
idation. Therefore, we elaborated a second route to 1d,
which started again with 4-hydroxyacetophenone (13). Its
4-toluenesulfonylhydrazone 19 was transformed to the
1,2,3-thiadiazole 1e. Reaction of 1e with epichlorohydrin
(20) gave 1d. The overall yield of 1d from 13 via 15, 17,
The extremely high reactivity of the 1,3-diradicals 2 pre-
destinates polymers with attached 1,2,3-thiadiazole rings
for photocrosslinking reactions. Several compounds 1
SYNTHESIS 2009, No. 15, pp 2539–2546
x
x.
x
x
.
2
0
0
9
Advanced online publication: 26.06.2009
DOI: 10.1055/s-0029-1216879; Art ID: T04409SS
© Georg Thieme Verlag Stuttgart · New York

2540
M. Al-Smadi et al.
PAPER
R
Ph
N
Ph
H
Ph
H
N
•
N
hν
R = H, alkyl, aryl
R
S
S
N
– N2
S
•
S
1
H
1a
2a
4a
– N2 Δ T or hν
rear
R
R
•
Ph
H
R
R
S
– S
S
R
•
S
R
5a
3
4
2
+ 2a
rear
Ph
H
R
R
Ph
H
Ph
H
S
S
S
S
S
5
Ph
H
S
R
R
R
R
(Z)-9a
(E)-9a
Scheme 2 Photolysis of 4-phenyl-1,2,3-thiadiazole (1a) to 2-ben-
zylidene-4-phenyl-1,3-dithiole [(Z/E)-9a]
S
6
5 + 5
(S)
– S
R
solubility. Figure 1 demonstrates the 1H and 13C chemical
shifts of 1c and its polymer 1c¢. The signals of the olefinic
part of 1c disappear and new signals of 1c¢ appear in the
saturated region. The NMR data of the 4-phenyl-1,2,3-
thiadiazole moiety are almost the same for monomer 1c
and polymer 1c¢.
R
n
R
R
S
S
7 (n = 1), 8 (n = 2)
R
S
R
2 + 5
R
S
The cationic ring-opening polymerization of oxirane 1d,
performed with boron trifluoride under the same condi-
tions as for 1c, was less uniform.28–30 Additionally, a par-
tial fragmentation of the 1,2,3-thiadiazole rings could not
be avoided. The polymer 1d¢ was still soluble in organic
solvents like chloroform or acetone, but the lack of unifor-
mity prompted us to exclude 1d¢ from further studies.
R
9
R
R
– S
R
R
S
10
R
R
Finally we tried another approach to polymers containing
1,2,3-thiadiazole rings (Scheme 5). The phenolic OH
group of 13 was alkylated with 1,3-dibromopropane (21)
to give ketone 22, whose 4-toluenesulfonylhydrazone 23
was subjected to the Hurd–Mori reaction.27 The reactivity
of the carbonyl group in 22 toward 4-toluenesulfonyl hy-
drazide (16) is much higher than the reactivity of the bro-
mo substituent. Thus, excellent yields of hydrazone 23
and 1,2,3-thiadiazole 1f could be obtained. The terminal
bromo group in 1f could then be used for the formation of
arylalkyl ethers. Whereas unsubstituted phenol (24) gen-
erated monomer thiadiazole 1g, the analogous reaction of
1f and 4-isopropenylphenol (25) led directly to polymer
1h¢. The obtained ochre powder turned out to be insoluble
in all common organic solvents. Its sulfur content was cor-
rect, its nitrogen content was too low.
S
R
2 + 2
S
R
11
R
S
R
+ S
R
R
S
S
12
Scheme 1 Formation of S-heterocycles by ring cleavage of 1,2,3-
thiadiazoles 1: 2,4-dialkylidene-1,3-dithietanes 6,2 3,5-dialkylidene-
1,2,4-trithiolanes 7,3,4 3,6-dialkylidene-1,2,4,5-tetrathianes 8,3 2-al-
kylidene-1,3-dithioles 9,5–10 thiophenes 10,3,6,7,9,11,12 1,4-dithiines
11,5,6,7,9 and 1,2,5-trithiepines 128
and 1b was 29% whereas the total yield for the alternate
process via 19 and 1e amounted to 47%.
When commercial poly(4-hydroxystyrene) (26) was re-
acted with 1f, an ochre powder 1i¢ was obtained, which
was soluble in acetone. Its nitrogen and sulfur content cor-
responded largely to intact 1,2,3-thiadiazole rings and a
complete alkylation of all phenolic OH groups. The pho-
tocrosslinking of the polymers 1c¢ and 1i¢ could be per-
The vinyl ether 1c and the oxirane 1d were polymerized
in the presence of the Lewis acid boron trifluoride–diethyl
ether complex. The cationic process was almost quantita-
tive (90–97%) and left the great majority of the 1,2,3-thia-
diazole rings intact, which is important for a good
Synthesis 2009, No. 15, 2539–2546 © Thieme Stuttgart · New York

PAPER
Photocrosslinking with 1,2,3-Thiadiazole
2541
H+
O
NNHTs
O
TsNHNH2 (16)
Br
K2CO3, KI
98%
O
HO
+
O
91%
13
14
15
17
N
N
RhCl(PPh3)3
DABCO
N
N
N
N
S
SOCl2
90%
+
O
S
O
S
O
64%
1b
(E)-1c
44:56
(Z)-1c
Scheme 3 Preparation of 4-[4-(prop-1-enyloxy)phenyl]-1,2,3-thiadiazole [(Z/E)-1c]
photocrosslinking by formation of 1,3-dithioles.
Scheme 6 illustrates the processes 1c¢→1c¢¢ and 1i¢→1i¢¢.
Due to the rigid cross-linking segment in 1c¢¢, such a pro-
cess is unlikely within a chain (intramolecular reaction).
The cross-linking segment of 1i¢¢ is more flexible. There-
fore, intra- and intermolecular photoreactions are possi-
ble.
O
N
N
S
MCPBA (18)
O
1b
36%
1d
13
O
63%
Cl
16 99%
20
NNHTs
N
How can the presumed type of photocrosslinking shown
in Scheme 6 be verified? For this purpose we reinvestigat-
ed the 13C NMR and IR characterization of model com-
pound 9a,31,32 which we obtained by irradiation of 1a in
benzene. The Z/E ratio amounted to 10:1. The E-isomer
has low solubility in toluene, so we could obtain the pure
(Z)-isomer by fractional crystallization. Its 13C NMR sig-
nals in CDCl3 range from d = 111.7–113.2 for the methine
CH of the 2-methylene-1,3-dithiole moiety, to d = 132.6–
134.3 for the Cq of the S-heterocycles and to d = 135.2–
136.7 for the Cq of the benzene rings. The remaining aro-
matic CH signals are between d = 125.6–128.8. The solid
N
SOCl2
76%
HO
HO
S
1e
19
Scheme 4 Preparation of 4-[4-(oxiran-2-ylmethoxy)phenyl]-1,2,3-
thiadiazole (1d)
1.08
Me
10.5
1.68
12.2
Me
3.97
69.6
CH
CH
1.85
22.5
5.43
109.5
6.46
141.4
H
n
H
O
13
O
state C NMR of the cross-linked polymers 2c¢¢ and 2i¢¢
7.04
115.1
158.4
160.1
123.3
7.06
116.7
H
H
exhibit strongly superimposed signals in this area 110 £ d
£ 140, but the resolution of the magic angle spinning mea-
surement was much too low in order to verify the 1,3-
dithiole substructure. Therefore, we had to rely on the IR
measurement in potassium bromide.
7.96
128.8
7.97
128.7
125.1
162.5
N
H
H
H
H
162.8
N
8.50
128.3
8.53
128.8
S
N
S
1c
N
Model compound 9a exhibits intense bands at 1578, 1556,
and 1484 cm–1,33 which appear also in IR spectra of poly-
dithiafulvenes.34,35 The IR spectra of the cross-linked
polymers 1c¢¢ and 1i¢¢ contain indeed strong, overlapping
bands in the region 1480–1500 and 1550–1600 cm–1. 2-
Benzylidene-4-phenyl-1,3-dithiole (9a) generates a red
1,3-dithiolium salt, soluble in trifluoroacetic acid.5 When
1c¢¢ and 1i¢¢ were treated with trifluoroacetic acid, the
ochre color changed to red-brown, but the cross-linked
polymers remained insoluble. We take the IR measure-
ments and the behavior toward trifluoroacetic acid as
1c
Figure 1 1H and 13C NMR data of the monomer (E)-1c and the po-
lymer 1c¢ (CDCl3, TMS, d).
formed in solution (benzene or dichloromethane) or in
thin neat films, which were spin-coated or produced by
evaporation of saturated solutions. The absorption maxi-
ma of 1c¢ and 1i¢ occur at 260 nm; additionally to this
p→p* transitions, n→p* transitions appear in the form of
an extended shoulder at about 310 nm (CH2Cl2).
Irradiations of the films with a mercury medium pressure good hints for the cross-linking type shown in Scheme 6.
lamp, equipped with a Vycor filter (lirr 230 nm) generat-
ed cross-linked polymers 1c¢¢, and 1i¢¢, which were totally
Summarizing the results, we can make the following
statement: Soluble polymers 1c¢ and 1d¢ could be pre-
insoluble in organic solvents. Exactly this behavior is a
pared by cationic polymerization of the 4-phenyl-1,2,3-
fundamental precondition for the application of 1c¢/1c¢¢
and 1i¢/1i¢¢ as negative photoresists. According to the re-
action of the model compound 1a→9a, we assumed a
thiadiazoles 1c and 1d, which contain polymerizable
functionalities in 4-position of the phenyl groups. In a sec-
Synthesis 2009, No. 15, 2539–2546 © Thieme Stuttgart · New York

2542
M. Al-Smadi et al.
PAPER
O
1c'
K2CO3, KI
Br
O
+
Br
Br
13
79%
Me
hν
22
21
S
16
(H+)
O
NNHTs
Me
O
n
Br
O
S
n
92%
1c''
23
N
SOCl2
96%
N
S
1i'
Br
O
1f
hν
OH
S
S
O
N
24
N
S
O
O
O
O
64%
1g
O
OH
25
1i''
58%
n
n
K2CO3
KI
Scheme 6 Photoreactions of the soluble polymers 1c¢ and 1i¢ to the
insoluble cross-linked polymers 1c¢¢ and 1i¢¢, respectively
N
1h′
1f
N
O
O
S
Melting points were determined on a Büchi melting point apparatus
and are uncorrected. The Bruker spectrometers AM 400 and ARX
1
400 served for the measurement of the H and 13C NMR spectra.
CDCl3 was used as solvent and TMS as internal standard, if not oth-
erwise stated. FT-IR spectra were recorded on a GX Perkin-Elmer
and IR spectra on a Beckman Acculab spectrophotometer. A Zeiss
MCS 224/234 diode array spectrophotometer was used for the UV
spectroscopy. Mass spectra were obtained on a Finnigan MAT 95
and a Micromass TOF spec E spectrometer. Column chromatogra-
phy was carried out on silica gel (60 M, 230–400 mesh, Macherey-
Nagel). Elemental analyses were performed in the Microanalytical
Laboratory of the Institute of Organic Chemistry of the University
of Mainz.
O
OH
26
N
1l′
N
O
S
Scheme 5 Preparation of the polymers 1h¢ and 1i¢
ond approach polymer 1i¢ was obtained by attaching
Synthesis of the Monomeric 1,2,3-Thiadiazoles
1,2,3-thiadiazole containing side chains to the main chain 4-(Allyloxy)acetophenone (15)
4-Hydroxyacetophenone (13, 5.2 g, 38.1 mmol), 3-bromoprop-1-
of poly(4-hydroxystyrene). The uniform polymers 1c¢ and
1i¢ have intact 1,2,3-thiadiazole rings, which show nitro-
gen extrusion on irradiation. The resulting 1,3-diradicals
rearrange partly to thioketenes, which then enter a cy-
cloaddition with the remaining 1,3-diradicals to form 1,3-
dithioles as cross-linking segments between the main
chains. These materials 1c¢¢ and 1i¢¢ are completely insol-
uble, so that the systems 1c¢/1c¢¢ and 1i¢/1i¢¢ fulfill the con-
ditions for negative photoresists. Since 1,2,3-thiadiazole
rings can also be cleaved by synchroton radiation and
electron beams, further resist techniques seem to be appli-
cable. A major advantage of the polymers 1c¢ and 1i¢ is
due to the fact that ‘vagabonding’ atomic sulfur is not
formed during the photocrosslinking. Therefore, high res-
olution of imaging techniques with these negative photo-
resists can be expected.
ene (14, 4.6 g, 38.3 mmol), K2CO3 (5.2 g, 37.5 mmol), and KI (4.6
g, 27.7 mmol) were heated in anhyd acetone (85 mL) to reflux for
40 h. The mixture was then stirred with H2O (60 mL) at r.t. for 10
min and extracted with CH2Cl2 (3 × 50 mL). The soln was dried
(MgSO4), concentrated, and purified by column filtration (silica gel,
8 × 15 cm, CH2Cl2) to give a viscous oil that solidified below 20 °C;
yield: 6.6 g (98%). The product was identified by comparison with
an authentic sample.26
1H NMR (CDCl3): d = 2.29 (s, 3 H, CH3), 4.32–4.37 (m, 2 H, CH2),
3
5.02–5.07 (m, Jcis = 10.0 Hz, 1 H, =CH2), 5.22–5.28 (m,
3Jtrans = 17.0 Hz, 1 H, =CH2), 5.78–5.83 (m, 1 H, =CH), 6.70/7.68
(AA¢BB¢, 4 H, Harom).
13C NMR (CDCl3): d = 25.7 (CH3), 68.2 (OCH2), 113.8, 129.9
(CHarom), 117.3 (=CH2), 129.7, 161.9 (arom-Cq), 132.0 (=CH),
195.8 (CO).
Synthesis 2009, No. 15, 2539–2546 © Thieme Stuttgart · New York

PAPER
Photocrosslinking with 1,2,3-Thiadiazole
2543
4-(Allyloxy)acetophenone 4-Toluenesulfonylhydrazone (17)
Ketone 15 (3.0 g, 17.0 mmol) was added to a boiling solution of
TsNHNH2 (16, 3.17 g, 17.02 mmol) in EtOH (15 mL). The mixture
was refluxed for 1 h and then concentrated till the product started to
precipitate. Recrystallization (EtOH) gave 17 (5.3 g, 91%) as a col-
orless powder; mp 138 °C.
4-[4-(Oxiran-2-ylmethoxy)phenyl]-1,2,3-thiadiazole (1d) by
Epoxidation of 1b
MCPBA (18, 0.78 g, 4.52 mmol) dissolved in anhyd CH2Cl2 (9 mL)
was added dropwise to a soln of 1b (0.70 g, 3.21 mmol) in anhyd
CH2Cl2 (10 mL) at 0 °C. The mixture was stirred vigorously at r.t.
for 6 h and at reflux for 3 h. The mixture was filtered and the soln
was washed with 10% NaOH (3 × 10 mL) and H2O (2 × 20 mL).
The dried (MgSO4) and concentrated solution was chromato-
graphed (silica gel, 3 × 80 cm, EtOH–CH2Cl2, 1:40). The first frac-
tion consisted of unreacted 1b and the second fraction of the product
1d (0.30 g, 36%); colorless crystals; mp 77–78 °C.
1H NMR (CDCl3): d = 2.11 (s, 3 H, CH3), 2.38 (s, 3 H, CH3), 4.50–
4.55 (m, 2 H, CH2), 5.25–5.29 (m, 3Jcis = 10.0 Hz, 1 H, =CH2), 5.38–
3
5.43 (m, Jtrans = 17.0 Hz, 1 H, =CH2), 5.98–6.03 (m, 1 H, =CH),
6.82/7.90 (AA¢BB¢, 4 H, Harom), 7.28/7.55 (AA¢BB¢, 4 H, Harom),
7.94 (s, 1 H, NH).
1H NMR (CDCl3): d = 2.75–2.79/2.90–2.95/3.35–3.39 (3 m, 3 H,
oxirane ring), 3.95–3.99/4.26–4.30 (2 m, 2 H, OCH2), 7.04/7.93
(AA¢BB¢, 4 H, benzene ring), 8.52 (s, 1 H, H5).
13C NMR (CDCl3): d = 13.2, 21.5 (CH3), 68.8 (OCH2), 114.4,
127.7, 128.1, 129.5 (CHarom), 117.8 (=CH2), 132.9 (=CH), 130.1,
135.6, 144.0, 159.8 (arom Cq), 152.6 (CN).
13C NMR (CDCl3): d = 44.5 (CH2, oxirane ring), 50.0 (CH, oxirane
ring), 68.9 (OCH2), 115.3, 128.8 (CHPh), 124.1, 159.4 (Cq-Ph),
128.5 (C5), 162.5 (C4).
MS (FD): m/z (%) = 344 (100) [M+].
Anal. Calcd for C18H20N2O3S (344.4): C, 62.77; H, 5.85; N, 8.13.
Found: C, 62.47; H, 5.82; N, 8.12.
MS (FD): m/z (%) = 234 (100) [M+].
4-[4-(Allyloxy)phenyl]-1,2,3-thiadiazole (1b); Typical Proce-
dure
Anal. Calcd for C11H10N2O2S: C, 56.40; H, 4.30; N, 11.96; S, 13.69.
Found: C, 56.63; H, 4.23; N, 11.93; S, 13.71.
Hydrazone 17 (2.0 g, 5.81 mmol) was added portionwise at r.t. to
freshly distilled SOCl2 (8.0 mL, 13.1 g, 110 mmol). The vigorously
stirred mixture started immediately to react. The temperature was
kept at 10–15 °C by cooling in an ice bath and stirred for 1 h and
this was continued at r.t. for 6 h. The excess SOCl2 was removed (1
kPa) and the residue purified by column chromatography (silica gel,
5 × 100 cm, toluene). After the first fraction of TsCl, 1b (1.1 g, 90%)
was obtained as a colorless powder; mp 74 °C.
4-Hydroxyacetophenone 4-Toluenesulfonylhydrazone (19)
4-Hydroxyacetophenone (13, 2.19 g, 16.0 mmol) was added to a hot
soln of TsNHNH2 (16, 3.0 g, 16.0 mmol) in EtOH (16 mL). The
mixture was refluxed for 1 h then concentrated till the product start-
ed to precipitate. The obtained yellowish powder was washed (cold
EtOH) and recrystallized (EtOH); yield: 4.8 g (99%); mp 93–94 °C.
1H NMR (DMSO-d6): d = 2.12 (s, 3 H, CH3), 2.36 (s, 3 H, CH3),
6.77/7.83 (AA¢BB¢, 4 H, Harom), 7.42/7.51 (AA¢BB¢, 4 H, Harom),
9.79 (s, 1 H, NH), 10.29 (s, 1 H, OH).
1H NMR (CDCl3): d = 4.58–4.63 (m, 2 H, CH2), 5.25–5.30 (m,
3
3Jcis = 10.0 Hz, 1 H, =CH2), 5.45–5.49 (m, Jtrans = 16.0 Hz, 1 H,
=CH2), 6.03–6.08 (m, 1 H, =CH), 7.00/7.93 (AA¢BB¢, 4 H, Harom),
8.50 (s, 1 H, H5).
13C NMR (DMSO-d6): d = 14.0, 20.9 (CH3), 115.0, 127.4, 127.5,
129.3 (CHarom), 128.3, 136.3, 143.1 (arom Cq), 153.4 (CN), 158.7
(arom CqO).
13C NMR (CDCl3): d = 68.8 (OCH2), 115.3, 128.7 (CHarom), 117.9
(=CH2), 132.9 (=CH), 128.4 (C5), 123.6, 159.5 (arom Cq), 162.6
(C4).
MS (EI): m/z (%) = 304 (13) [M+], 149 (100), 119 (55), 92 (53).
Anal. Calcd for C15H16N2O3S (304.4): C, 59.19; H, 5.30; N, 9.20.
Found: C, 59.22; H, 5.31; N, 9.18.
MS (FD): m/z (%) = 218 (100) [M+].
HRMS: m/z [M+] calcd for C11H10N2OS: 218.0514; found:
218.0518.
4-(1,2,3-Thiadiazol-4-yl)phenol (1e)
Following the typical procedure for 1b using 19 (3.0 g, 9.87 mmol)
yielded 1e (1.3 g, 76%) as an ochre powder; mp 166 °C. The product
was identified by comparison with an authentic sample.36,37
(Z/E)-4-[4-(Prop-2-enyloxy)phenyl]-1,2,3-thiadiazole [(E/Z)-1c]
DABCO (0.69 g, 6.37 mmol), RhCl(PPh3)3 (0.5 g, 0.54 mmol), and
1b (1.14 g, 5.20 mmol) were added to a mixture of EtOH (220 mL),
toluene (80 mL), and H2O (30 mL). The reaction was performed at
85 °C under an N2 atmosphere [monitored by TLC (silica gel, tolu-
ene)]. After 30 h the volatile parts were evaporated (1.0 kPa) and the
residue purified by column chromatography (silica gel, 3 × 100 cm,
CH2Cl2–EtOH, 25:1); 1c (0.70 g, 64%) was the first fraction; color-
less crystals; mp 81–82 °C; ratio Z/E 56:44 (1H NMR). Later frac-
tions consist of starting compound 1b and some 4-(1,2,3-thiadiazol-
4-yl)phenol (1e), which was formed by ether cleavage.
1H NMR (DMSO-d6): d = 6.95/7.97 (AA¢BB¢, 4 H, Harom), 8.97 (s,
1 H, OH), 9.39 (s, 1 H, 5-H).
13C NMR (DMSO-d6): d = 116.0, 128.7 (CHarom), 121.8, 158.6
(arom Cq), 130.7 (C5).
4-[4-(Oxiran-2-ylmethoxy)phenyl]-1,2,3-thiadiazole (1d) by
Reaction of 1e with ( )-Epichlorohydrin (20)
A mixture of thiadiazole 1e (0.23 g, 1.29 mmol), ( )-2-(chloro-
methyl)oxirane (20, 0.23 g, 2.49 mmol), K2CO3 (O.30 g, 2.16
mmol), and KI (0.30 g, 1.81 mmol) in anhyd acetone (30 mL) was
refluxed for 30 h. The mixture was treated with H2O (20 mL) and
extracted with CH2Cl2 (3 × 25 mL). The dried (MgSO4) organic
phase was evaporated and the residue purified by column chroma-
tography (silica gel, 4 × 70 cm, CH2Cl2–EtOH, 20:1) to give 1d as
colorless crystals; yield: 0.20 g (63%); mp 77–78 °C.
1H NMR (CDCl3): d [(E)-1c] = 1.65–1.69 (m, 3 H, CH3), 5.41–5.46
3
3
(m, J = 15.0 Hz, 1 H, =CH), 6.43–6.48 (m, J = 15.0 Hz, 1 H,
=CH), 7.06/7.96 (AA¢BB¢, 4 H, Harom), 8.53 (s, 1 H, H5);
d [(Z)-1c] = 1.70–1.74 (m, 3 H, CH3), 4.92–4.97 (m, 3J = 8.0 Hz, 1
H, =CH), 6.40–6.45 (m, 3J = 8.0 Hz, 1 H, =CH), 7.09/7.98
(AA¢BB¢, 4 H, Harom), 8.53 (s, 1 H, H5).
13C NMR (CDCl3): d [(E)-1c] = 12.2 (CH3), 109.5, 141.1 (=CH),
116.7, 128.8 (CHarom), 125.1, 158.4 (arom Cq), 128.8 (C5), 162.5
(C4).
4-(3-Bromopropoxy)acetophenone (22)
1,3-Dibromopropane (21, 30.0 g, 148.6 mmol), ketone 13 (2.0 g,
14.9 mmol), and K2CO3 (20.0 g, 145.0 mmol) in anhyd acetone (80
mL) were refluxed for 40 h. The filtered mixture was evaporated (1
kPa); the solvent and excess 21 distilled off. The residue was puri-
fied by column chromatography [silica gel, 5 × 100 cm, petroleum
MS (FD): m/z (%) = 218 (24) [M+], 190 (87), 158 (32), 148 (100),
77 (41).
Anal. Calcd for C11H10N2OS (218.3): C, 60.53; H, 4.62; N, 12.83.
Found: C, 60.62; H, 4.65; N, 12.81.
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2544
M. Al-Smadi et al.
PAPER
ether (bp 40–70 °C) to remove residual 21 and then EtOAc–CH2Cl2,
35:65]. Product 22 was obtained as an almost colorless, viscous oil;
yield: 3.0 g (79%). The product was identified by comparison with
an authentic sample.38
MS (EI): m/z (%) = 312 (55) [M+], 284 (86), 207 (57), 151 (100).
Anal. Calcd for C17H16N2O2S (312.4): C, 65.36; H, 5.16; N, 8.97.
Found: C, 65.38; H, 5.21; N, 8.93.
1H NMR (CDCl3): d = 2.26–2.30 (m, 2 H, CH2), 2.50 (s, 3 H, CH3),
3.55 (t, 3J = 6.4 Hz, 2 H, CH2Br), 4.11 (t, 3J = 5.9 Hz, 2 H, OCH2),
6.88/7.86 (AA¢BB¢, 4 H, Harom).
Synthesis of Polymers
Polymer 1c¢; Typical Procedure
(E/Z)-1c (0.2 g, 0.92 mmol), dissolved in anhyd CH2Cl2 (4 mL), was
treated under N2 at 0 °C with BF3·OEt2 (2 drops). The mixture was
stirred at 0 °C for 30 min and at r.t. for 90 min and the reaction was
quenched by addition of MeOH (5 mL). The volatile parts were
evaporated, the filtered residue washed (cold MeOH) and dried in
vacuo (0.1 kPa) for 48 h to give 1c¢ (195 mg, 97%) as an ochre prod-
uct that started to melt at 62 °C and decomposed at 167 °C. It was
soluble in many organic solvents. In order to remove small oligo-
mers, which can be seen in the MS (FD), we precipitated it several
times from THF.
13C NMR (CDCl3): d = 26.2 (CH3), 29.6 (CH2), 32.1 (CH2Br), 65.6
(CH2O), 114.2, 130.5 (CHarom), 130.5, 162.6 (arom Cq), 196.5 (CO).
4-(3-Bromopropoxy)acetophenone 4-Toluenesulfonylhydra-
zone (23)
Ketone 22 (1.5 g, 5.83 mmol) and TsNHNH2 (16, 1.1 g, 5.91 mmol)
were heated in EtOH (8 mL) to reflux. After 1 h the soln was con-
centrated till the product began to precipitate. The colorless powder
was washed (cold EtOH) and recrystallized (EtOH); yield: 2.3 g
(92%); mp 126 °C.
3
1H NMR (CDCl3): d = 1.08 (d, J = 6.4 Hz, 3 H, CH3), 1.82–1.86
(m, 1 H, CH), 3.97 (t, 3J = 5.7 Hz, 1 H, OCH), 7.04/7.97 (AA¢BB¢,
4 H, Harom), 8.50 (s, 1 H, H5).
1H NMR (CDCl3): d = 2.11 (s, 3 H, CH3), 2.26–2.30 (m, 2 H, CH2),
2.38 (s, 3 H, CH3), 3.58 (t, 3J = 6.3 Hz, 2 H, CH2Br), 4.08 (t, 3J = 5.9
Hz, 2 H, OCH2), 6.82/7.90 (AA¢BB¢, 4 H, Harom), 7.29/7.57
(AA¢BB¢, 4 H, Harom), 7.91 (s, 1 H, NH).
13C NMR (CDCl3): d = 10.5 (CH3), 22.5 (CH), 69.6 (OCH), 115.1,
128.7 (CHarom), 123.3, 160.1 (arom Cq), 128.3 (C5), 162.8 (C4).
13C NMR (CDCl3): d = 13.2, 21.5 (CH3), 29.7, 32.2, 65.4 (CH2),
114.2, 127.8, 128.1, 129.5 (CHarom), 130.2, 135.6, 144.0, 152.5
(arom Cq), 152.5 (CN).
The NMR data are related to the repeat unit; end groups could not
be identified. Comparison of the elemental analysis (Table 1) with
the data of the monomer reveals that the 1,2,3-thiadiazole rings
were intact.
MS (FD): m/z (%) = 424/426 (100) [M+, Br isotope pattern].
Anal. Calcd for C18H21BrN2O3S (425.35): C, 50.83; H, 4.98; Br,
18.79; N, 6.59; S, 7.54. Found: C, 50.88; H, 5.19; Br, 18.45; N,
6.60; S, 7.44.
Polymer 1d¢
The cationic polymerization of 1d to 1d¢ was performed according
to typical procedure to give 1c¢. A yellow solid (90%) was obtained,
which started to melt at 58 °C and decomposed above 190 °C. The
1H and 13C NMR characterization of the well-soluble product
showed a large number of broad signals, which hint to a non-uni-
form ring-opening polymerization. The elemental analysis revealed
a too low content of N (10.93%) and S (11.87%) compared to the
monomer: N (11.89%), S (13.64%). These values permit the con-
clusion that 8–13% of the 1,2,3-thiadiazole rings did not survive the
polymerization. Therefore we did not continue our studies with
polymer 1d¢.
4-[4-(3-Bromopropoxy)phenyl]-1,2,3-thiadiazole (1f)
Hydrazone 23 (0.5 g, 1.18 mmol) was slowly added to freshly dis-
tilled SOCl2 (24.0 mL, 39.3 g, 330 mmol). The vigorously stirred
mixture started immediately to react at r.t.; an ice-water bath was
used for cooling. Further hydrazone 23 (1.95 g, 458 mmol) was add-
ed in small portions over 20 min. The mixture was stirred at r.t. for
6 h and then excess SOCl2 was removed and the residue purified by
column chromatography (silica gel, 5 × 100 cm, toluene). The 1st
fraction consisted of TsCl and the 2nd fraction contained the prod-
uct 1f (0.30 g, 96%) as colorless crystals; mp 95–97 °C.
Polymer 1h¢
1H NMR (CDCl3): d = 2.30–2.36 (m, 2 H, CH2), 3.61 (t, 3J = 6.4 Hz,
2 H, CH2Br), 4.15 (t, 3J = 5.9 Hz, 2 H, OCH2), 6.99/7.96 (AA¢BB¢,
4 H, Harom), 8.50 (s, 1 H, H5).
4-Isopropenylphenol (25, 0.33 g, 2.44 mmol), 1,2,3-thiadiazole 1f
(0.73 g, 2.44 mmol), K2CO3 (0.35 g, 2.52 mmol), and KI (0.78 g,
4.70 mmol) were heated in anhyd acetone (60 mL) to reflux. After
40 h the mixture was stirred with H2O (30 mL). A pale brown pre-
cipitate was filtered off, washed with CH2Cl2 and dried in vacuo
(0.1 kPa). The product could not be dissolved in NMR solvents such
as CDCl3, acetone-d6, DMSO-d6, etc.
13C NMR (CDCl3): d = 29.7, 32.3, 65.6 (CH2), 115.2, 128.8
(CHarom), 123.9, 159.7 (arom Cq), 128.4 (C5), 162.6 (C4).
MS (EI): m/z (%) 300/298 (5) [M+, Br isotope pattern], 149 (100).
Anal. Calcd for C11H11BrN2OS: C, 44.16; H, 3.71; N, 9.36. Found:
C, 43.79; H, 3.99; N, 9.06.
Anal. Calcd for the repeat unit C20H20O2N2S: C, 68.16; H, 5.72; N,
7.95; S, 9.10. Found for the polymer 1h¢: C, 69.44; H, 6.64; N, 7.21;
S, 8.91. These values reveal that almost all OH groups reacted with
the bromide and that the majority of 1,2,3-thiadiazole rings were
kept intact. Due to the insolubility, the material cannot be used as
negative photoresist.
4-[4-(3-Phenoxypropoxy)phenyl]-1,2,3-thiadiazole (1g)
Phenol (24, 0.1 g, 1.06 mmol), 1f (0.30 g, 1.00 mmol), K2CO3 (0.15
g, 1.09 mmol), and KI (0.35 g, 2.11 mmol) were heated to reflux in
anhyd acetone (30 mL). After 30 h, the mixture was treated with
H2O (40 mL) and extracted with CH2Cl2 (3 × 40 mL). The dried
(MgSO4) organic phase was evaporated and the residue recrystal-
lized (CH2Cl2) to give an ochre powder; yield: 0.2 g (64%) ; mp 67–
68 °C.
Polymer 1i¢
1,2,3-Thiadiazole 1f (0.33 g, 1.10 mmol), which bears a bromo sub-
stituent, was reacted with poly(4-hydroxystyrene) (26, 0.12 g, 1.00
mmol related to monomer, Mw = 5800), K2CO3 (0.15 g, 1.08
mmol), and KI (0.36 g, 2.17 mmol) in anhyd acetone (40 mL). The
mixture was heated to reflux for 30 h and then H2O (30 mL) was
added to the vigorously stirred mixture. Extraction with CH2Cl2 (3
× 50 mL) gave an organic phase, which was dried (MgSO4) and
evaporated. The obtained ochre powder 1i¢ (0.33 g, 98%) was
washed (cold Et2O) and purified by dissolving and precipitating
1H NMR (CDCl3): d = 2.80–2.85 (m, 2 H, CH2), 4.14–4.19 (m, 2 H,
CH2), 4.20–4.26 (m, 2 H, OCH2), 6.90–6.95 (m, 3 H, Harom), 7.03/
7.96 (AA¢BB¢, 4 H, Harom), 7.25–7.29 (m, 2 H, Harom), 8.49 (s, 1 H,
H5).
13C NMR (CDCl3): d = 29.4, 64.3, 64.8 (CH2), 114.6, 115.2, 120.8,
128.8, 129.5 (CHarom), 123.7, 158.9, 159.9 (arom Cq), 128.3 (C5),
162.7 (C4).
Synthesis 2009, No. 15, 2539–2546 © Thieme Stuttgart · New York

PAPER
Photocrosslinking with 1,2,3-Thiadiazole
2545
Table 1 Change of the Elemental Composition by Photocrosslinking of the Polymers 1c¢ and 1i¢ to 1c¢¢ and 1i¢¢, Respectively
Analysis (%)
C
H
N
S
Calcd for repeat unit C11H10N2OS
60.53
60.90
67.99
64.46
67.43
67.81
73.12
78.41
4.62
5.01
5.34
5.76
5.36
5.66
6.20
7.25
12.83
12.60
0.21
0.53
8.28
8.09
0.31
0.74
14.69
14.58
16.55
16.42
9.47
1c¢ found
1c¢¢ (film)
1c¢¢ (soln)
Calcd for repeat unit C19H18N2O2S
1i¢ found
1i¢¢ (film)
1i¢¢ (soln)
9.37
10.48
10.63
from acetone. The carefully dried yellow-ochre product (0.31 g,
92%) started to melt at 70 °C and decomposed above 110 °C.
Acknowledgment
We are grateful to the Deutsche Forschungs-Gemeinschaft, the
Fonds der Chemischen Industrie and the Centre of Materials Sci-
ence of the University of Mainz for financial support.
1H NMR (acetone-d6): d = 1.23–1.29 (m, 2 H, CH2), 2.25–2.31 (m,
2 H, CH2), 3.01–3.07 (m, 1 H, CH), 3.43–3.49 (m, 2 H, OCH2),
4.12–4.19 (m, 2 H, OCH2), 6.63–6.69 (m, 4 H, Harom), 7.09/8.08
(AA¢BB¢, 4 H, Harom), 9.24 (s, 1 H, H5). The data are related to the
repeat units, in which the OH groups have completely reacted.
References
13C NMR (acetone-d6): d = 22.9, 23.1 (CH2), 33.8 (CH), 68.7, 68.7
(CH2), 115.9, 115.9, 120.1, 124.9, 129.5, 130.7, 155.8, 160.8, 163.7
(arom and heteroarom CH and Cq).
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Photoreactions
(Z)-2-Benzylidene-4-phenyl-1,3-dithiole (Z-9a); Photochemis-
try of the Model Compound 1a
4-Phenyl-1,2,3-thiadiazole27,39 (1a, 1.62 g, 10.0 mmol), dissolved in
O2-free, anhyd benzene (600 mL) was irradiated in an N2 atmo-
sphere with a 450-W Hanovia medium pressure lamp, equipped
with a Vycor filter (l 230 nm). When the TLC control (silica gel,
toluene) indicated the complete consumption of 1a, the solvent was
evaporated and the residue (1.34 g, 100%) purified by column fil-
tration (silica gel, 10 × 15 cm, HCO2H) to give (Z/E)-2-ben-
zylidene-4-phenyl-1,3-dithiole [(E/Z)-9a] (0.94 g, 70%) as
colorless crystals. The identification was achieved by comparison
with an authentic sample.25 Crystallization (MeOH) afforded the
pure (Z)-2-benzylidene-4-phenyl-1,3-dithiole [(Z)-9a]; mp 207 °C.
1H NMR (DMSO-d6): d = 6.73 (s, 1 H, =CHPh), 7.19 (s, 1 H, H5),
7.31–7.54 (m, 10 H, Harom).
13C NMR (CDCl3): d = 111.7 (HC5), 113.2 (exo-CH), 125.6, 126.2,
126.6, 128.3, 128.5, 128.8 (CHarom), 132.6 (Cq-2), 134.3 (Cq-4),
135.2, 136.7 (arom Cq).
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Photocrosslinking of the Polymers; General Procedure
Sat. solns of 1c¢ or 1i¢ in CH2Cl2, CHCl3, acetone were used for the
formation of films by spin-coating (DELTA T) or by evaporation on
quartz plates (1 × 3.5 cm). Analogous experiments were made with
concentrated solutions of 1c¢ or 1i¢ [polymer (100 mg) in CH2Cl2
(200 mL)]. A 450-W Hanovia medium pressure lamp, equipped
with a Vycor filter (l 230 nm) served for the irradiation of the
films or solns. In both cases N2 was evolved and after an irradiation
period of 20 min (film) or 60–100 min (soln) an ochre material was
obtained, which was insoluble in organic solvents (including sol-
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(13) Katritzky, A. R.; Moyano, E. L.; Yranzo, G.; Singh, S. K.
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The elemental analyses (Table 1) revealed a negligible N content
and a preserved S content in 1c¢¢ and 1i¢¢.
Synthesis 2009, No. 15, 2539–2546 © Thieme Stuttgart · New York

2546
M. Al-Smadi et al.
PAPER
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Synthesis 2009, No. 15, 2539–2546 © Thieme Stuttgart · New York