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Synthesis 2009(15): 2539-2546  
DOI: 10.1055/s-0029-1216879
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

1,2,3-Thiadiazoles with Unsaturated Side Chains; Synthesis, Polymerization, and Photocrosslinking

Mousa Al-Smadi*a,b, Norbert Hanoldb, Helga Kalbitzb, 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;

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Publication History

Received 23 February 2009
Publication Date:
26 June 2009 (online)

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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 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.

Key words

cyclodimerization - cycloelimination - heterocycles - photochemistry - photoresists

1,2,3-Thiadiazoles 1 represent a prominent class of heterocycles that have attracted attention for their interesting pharmacological and biological properties, but also because they can be used for the preparation of various sulfur-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 intermediates. [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 formation 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]

The extremely high reactivity of the 1,3-diradicals 2 predestinates polymers with attached 1,2,3-thiadiazole rings for photocrosslinking reactions. Several compounds 1 with unsaturated side chains [¹4-²4] 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 drawback for the fabrication of negative photoresists. [²0] [²¹] Therefore, we attempted now to find systems with fairly clean photoprocesses 1 to 9. The dimers 9, dithiafulvenes, have a much lower tendency for secondary sulfur extrusion than other dimers.

4-Phenyl-1,2,3-thiadiazole (1a) fulfills the above-mentioned­ preconditions as a model compound in a nearly perfect manner. After light-induced nitrogen extrusion, a 1,3-diradical 2a is formed, in which the hydrogen atom has a high migration ability 2a→5a (Scheme  [²] ). The generated 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 (λirr ≥230 nm). Apart from 9a some polymers are formed in the photocleavage of 1a, but the other possible reaction routes leading to 3, 6, 7, 8, 10, 11, and 12 can be excluded. [5] [²5]

Our task was then to synthesize 1,2,3-thiadiazoles with 4-aryl substituents, which permit cationic polymerization.

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-alkylidene-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 12 [8]

In order to attach an olefinic chain to the 4-phenyl substituent in 1a, we prepared first 4-(allyloxy)acetophenone (15) by the almost quantitative alkylation of 4-hydroxy­acetophenone (13) with allyl bromide (14) (Scheme  [³] ). [²6] 4-Toluenesulfonyl hydrazide (16) yielded hydrazone 17, which was subjected to Hurd-Mori reaction [²7] 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 chloro­tris(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 moderate, because the thiadiazole ring itself was sensitive to oxidation. 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, and 1b was 29% whereas the total yield for the alternate process via 19 and 1e amounted to 47%.

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 quantitative (90-97%) and left the great majority of the 1,2,3-thia­diazole rings intact, which is important for a good 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′.

The cationic ring-opening polymerization of oxirane 1d, performed with boron trifluoride under the same conditions as for 1c, was less uniform. [²8-³0] Additionally, a partial 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 uniformity prompted us to exclude 1d′ from further studies.

Scheme 2 Photolysis of 4-phenyl-1,2,3-thiadiazole (1a) to 2-ben­zylidene-4-phenyl-1,3-dithiole [(Z/E)-9a]

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 hydrazide (16) is much higher than the reactivity of the bromo 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) generated 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 correct, its nitrogen content was too low.

When commercial poly(4-hydroxystyrene) (26) was reacted with 1f, an ochre powder 1i′ was obtained, which was soluble in acetone. Its nitrogen and sulfur content corresponded largely to intact 1,2,3-thiadiazole rings and a complete alkylation of all phenolic OH groups. The photocrosslinking of the polymers 1c′ and 1i′ could be performed in solution (benzene or dichloromethane) or in thin neat films, which were spin-coated or produced by evaporation of saturated solutions. The absorption maxima of 1c′ and 1i′ occur at 260 nm; additionally to this π→π* transitions, n→π* transitions appear in the form of an extended shoulder at about 310 nm (CH2Cl2).

Scheme 3 Preparation of 4-[4-(prop-1-enyloxy)phenyl]-1,2,3-thiadiazole [(Z/E)-1c]

Scheme 4 Preparation of 4-[4-(oxiran-2-ylmethoxy)phenyl]-1,2,3-thiadiazole (1d)

Figure 1  ¹H and ¹³C NMR data of the monomer (E)-1c and the polymer 1c′ (CDCl3, TMS, δ).

Irradiations of the films with a mercury medium pressure lamp, equipped with a Vycor filter (λirr ≥230 nm) generated cross-linked polymers 1c′′, and 1i′′, which were totally insoluble in organic solvents. Exactly this behavior is a fundamental precondition for the application of 1c′/1c′′ and 1i′/1i′′ as negative photoresists. According to the reaction of the model compound 1a→9a, we assumed a 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 process is unlikely within a chain (intramolecular reaction). The cross-linking segment of 1i′′ is more flexible. Therefore, intra- and intermolecular photoreactions are possible.

How can the presumed type of photocrosslinking shown in Scheme  [6] be verified? For this purpose we reinvestigated the ¹³C NMR and IR characterization of model compound 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 signals in CDCl3 range from δ = 111.7-113.2 for the methine CH of the 2-methylene-1,3-dithiole moiety, to δ = 132.6-134.3 for the Cq of the S-heterocycles and to δ = 135.2-136.7 for the Cq of the benzene rings. The remaining aromatic CH signals are between δ = 125.6-128.8. The solid state ¹³C NMR of the cross-linked polymers 2c′′ and 2i′′ exhibit strongly superimposed signals in this area 110 ≤ δ ≤ 140, but the resolution of the magic angle spinning measurement 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.

Scheme 5 Preparation of the polymers 1h′ and 1i′

Scheme 6 Photoreactions of the soluble polymers 1c′ and 1i′ to the insoluble cross-linked polymers 1c′′ and 1i′′, respectively

Model compound 9a exhibits intense bands at 1578, 1556, and 1484 cm-¹, [³³] which appear also in IR spectra of polydithiafulvenes. [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 measurements and the behavior toward trifluoroacetic acid as good hints for the cross-linking type shown in Scheme  [6] .

Summarizing the results, we can make the following statement: Soluble polymers 1c′ and 1d′ could be prepared by cationic polymerization of the 4-phenyl-1,2,3-thiadiazoles 1c and 1d, which contain polymerizable functionalities in 4-position of the phenyl groups. In a second approach polymer 1i′ was obtained by attaching 1,2,3-thiadiazole containing side chains to the main chain of poly(4-hydroxystyrene). The uniform polymers 1c′ and 1i′ have intact 1,2,3-thiadiazole rings, which show nitrogen extrusion on irradiation. The resulting 1,3-diradicals rearrange partly to thioketenes, which then enter a cycloaddition 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 insoluble, so that the systems 1c′/1c′′ and 1i′/1i′′ fulfill the conditions 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 applicable. 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 resolution of imaging techniques with these negative photoresists can be expected.

Melting points were determined on a Büchi melting point apparatus and are uncorrected. The Bruker spectrometers AM 400 and ARX 400 served for the measurement of the ¹H and ¹³C NMR spectra. CDCl3 was used as solvent and TMS as internal standard, if not otherwise 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 chromatography 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.

Synthesis of the Monomeric 1,2,3-Thiadiazoles4-(Allyloxy)acetophenone (15)

4-Hydroxyacetophenone (13, 5.2 g, 38.1 mmol), 3-bromoprop-1-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): δ = 2.29 (s, 3 H, CH3), 4.32-4.37 (m, 2 H, CH2), 5.02-5.07 (m, ³ J cis  = 10.0 Hz, 1 H, =CH2), 5.22-5.28 (m, ³ J trans  = 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): δ = 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).

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 colorless powder; mp 138 ˚C.

¹H NMR (CDCl3): δ = 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, ³ J cis  = 10.0 Hz, 1 H, =CH2), 5.38-5.43 (m, ³ J trans  = 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).

¹³C NMR (CDCl3): δ = 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).

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.

4-[4-(Allyloxy)phenyl]-1,2,3-thiadiazole (1b); Typical Procedure

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.

¹H NMR (CDCl3): δ = 4.58-4.63 (m, 2 H, CH2), 5.25-5.30 (m, ³ J cis  = 10.0 Hz, 1 H, =CH2), 5.45-5.49 (m, ³ J trans  = 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 (CDCl3): δ = 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 (FD): m/z (%) = 218 (100) [M+].

HRMS: m/z [M+] calcd for C11H10N2OS: 218.0514; found: 218.0518.

( 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, toluene)]. 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; colorless crystals; mp 81-82 ˚C; ratio Z/E 56:44 (¹H NMR). Later fractions consist of starting compound 1b and some 4-(1,2,3-thiadiazol-4-yl)phenol (1e), which was formed by ether cleavage.

¹H NMR (CDCl3): δ [(E)-1c] = 1.65-1.69 (m, 3 H, CH3), 5.41-5.46 (m, ³ J = 15.0 Hz, 1 H, =CH), 6.43-6.48 (m, ³ J = 15.0 Hz, 1 H, =CH), 7.06/7.96 (AA′BB′, 4 H, Harom), 8.53 (s, 1 H, H5); δ [(Z)-1c] = 1.70-1.74 (m, 3 H, CH3), 4.92-4.97 (m, ³ J = 8.0 Hz, 1 H, =CH), 6.40-6.45 (m, ³ J = 8.0 Hz, 1 H, =CH), 7.09/7.98 (AA′BB′, 4 H, Harom), 8.53 (s, 1 H, H5).

¹³C NMR (CDCl3): δ [(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).

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.

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 chromatographed (silica gel, 3 × 80 cm, EtOH-CH2Cl2, 1:40). The first fraction 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): δ = 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): δ = 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 (%) = 234 (100) [M+].

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.

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 started 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-d 6): δ = 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).

¹³C NMR (DMSO-d 6): δ = 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).

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.

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]

¹H NMR (DMSO-d 6): δ = 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-d 6): δ = 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-(chloro­methyl)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 chromatography (silica gel, 4 × 70 cm, CH2Cl2-EtOH, 20:1) to give 1d as colorless crystals; yield: 0.20 g (63%); mp 77-78 ˚C.

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 purified by column chromatography [silica gel, 5 × 100 cm, petroleum 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]

¹H NMR (CDCl3): δ = 2.26-2.30 (m, 2 H, CH2), 2.50 (s, 3 H, CH3), 3.55 (t, ³ J = 6.4 Hz, 2 H, CH2Br), 4.11 (t, ³ J = 5.9 Hz, 2 H, OCH2), 6.88/7.86 (AA′BB′, 4 H, Harom).

¹³C NMR (CDCl3): δ = 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-Toluenesulfonylhydrazone (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 concentrated till the product began to precipitate. The colorless powder was washed (cold EtOH) and recrystallized (EtOH); yield: 2.3 g (92%); mp 126 ˚C.

¹H NMR (CDCl3): δ = 2.11 (s, 3 H, CH3), 2.26-2.30 (m, 2 H, CH2), 2.38 (s, 3 H, CH3), 3.58 (t, ³ J = 6.3 Hz, 2 H, CH2Br), 4.08 (t, ³ J = 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): δ = 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).

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.

4-[4-(3-Bromopropoxy)phenyl]-1,2,3-thiadiazole (1f)

Hydrazone 23 (0.5 g, 1.18 mmol) was slowly added to freshly distilled 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 added 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 product 1f (0.30 g, 96%) as colorless crystals; mp 95-97 ˚C.

¹H NMR (CDCl3): δ = 2.30-2.36 (m, 2 H, CH2), 3.61 (t, ³ J = 6.4 Hz, 2 H, CH2Br), 4.15 (t, ³ J = 5.9 Hz, 2 H, OCH2), 6.99/7.96 (AA′BB′, 4 H, Harom), 8.50 (s, 1 H, H5).

¹³C NMR (CDCl3): δ = 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.

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 recrystallized (CH2Cl2) to give an ochre powder; yield: 0.2 g (64%) ; mp 67-68 ˚C.

¹H NMR (CDCl3): δ = 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): δ = 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).

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.

Synthesis of PolymersPolymer 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 product that started to melt at 62 ˚C and decomposed at 167 ˚C. It was soluble in many organic solvents. In order to remove small oligomers, which can be seen in the MS (FD), we precipitated it several times from THF.

¹H NMR (CDCl3): δ = 1.08 (d, ³ J = 6.4 Hz, 3 H, CH3), 1.82-1.86 (m, 1 H, CH), 3.97 (t, ³ J = 5.7 Hz, 1 H, OCH), 7.04/7.97 (AA′BB′, 4 H, Harom), 8.50 (s, 1 H, H5).

¹³C NMR (CDCl3): δ = 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).

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.

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-uniform 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 conclusion 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′.

Polymer 1h′

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 precipitate 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-d 6, DMSO-d 6, etc.

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.

Polymer 1i′

1,2,3-Thiadiazole 1f (0.33 g, 1.10 mmol), which bears a bromo substituent, was reacted with poly(4-hydroxystyrene) (26, 0.12 g, 1.00 mmol related to monomer, M w = 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 from acetone. The carefully dried yellow-ochre product (0.31 g, 92%) started to melt at 70 ˚C and decomposed above 110 ˚C.

¹H NMR (acetone-d 6): δ = 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.

¹³C NMR (acetone-d 6): δ = 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).

Elemental analysis in Table  [¹] .

Photoreactions( Z )-2-Benzylidene-4-phenyl-1,3-dithiole ( Z -9a); Photochemistry of the Model Compound 1a

4-Phenyl-1,2,3-thiadiazole [²7] [³9] (1a, 1.62 g, 10.0 mmol), dissolved in O2-free, anhyd benzene (600 mL) was irradiated in an N2 atmosphere with a 450-W Hanovia medium pressure lamp, equipped with a Vycor filter (λ ≥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 filtration (silica gel, 10 × 15 cm, HCO2H) to give (Z/E)-2-benzylidene-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-d 6): δ = 6.73 (s, 1 H, =CHPh), 7.19 (s, 1 H, H5), 7.31-7.54 (m, 10 H, Harom).

¹³C NMR (CDCl3): δ = 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).

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 (λ ≥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 solvents like NMP or 1,2-dichlorobenzene).

The elemental analyses (Table  [¹] ) revealed a negligible N content and a preserved S content in 1c′′ and 1i′′.

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 4.62 12.83 14.69
1c′ found 60.90 5.01 12.60 14.58
1c′′ (film) 67.99 5.34  0.21 16.55
1c′′ (soln) 64.46 5.76  0.53 16.42
Calcd for repeat unit C19H18N2O2S 67.43 5.36   8.28  9.47
1i′ found 67.81 5.66  8.09  9.37
1i′′ (film) 73.12 6.20  0.31 10.48
1i′′ (soln) 78.41 7.25  0.74 10.63

Acknowledgment

We are grateful to the Deutsche Forschungs-Gemeinschaft, the Fonds der Chemischen Industrie and the Centre of Materials Science of the University of Mainz for financial support.

28

For the polymerization of related phenylglycidyl ethers see refs. 29 and 30.

31

The ¹³C NMR signals of 9a published in ref. 32 cannot be correct, because they contain too many CH and too few Cq signals.

28

For the polymerization of related phenylglycidyl ethers see refs. 29 and 30.

31

The ¹³C NMR signals of 9a published in ref. 32 cannot be correct, because they contain too many CH and too few Cq signals.

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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-alkylidene-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 12 [8]

Scheme 2 Photolysis of 4-phenyl-1,2,3-thiadiazole (1a) to 2-ben­zylidene-4-phenyl-1,3-dithiole [(Z/E)-9a]

Scheme 3 Preparation of 4-[4-(prop-1-enyloxy)phenyl]-1,2,3-thiadiazole [(Z/E)-1c]

Scheme 4 Preparation of 4-[4-(oxiran-2-ylmethoxy)phenyl]-1,2,3-thiadiazole (1d)

Figure 1  ¹H and ¹³C NMR data of the monomer (E)-1c and the polymer 1c′ (CDCl3, TMS, δ).

Scheme 5 Preparation of the polymers 1h′ and 1i′

Scheme 6 Photoreactions of the soluble polymers 1c′ and 1i′ to the insoluble cross-linked polymers 1c′′ and 1i′′, respectively