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Open AccessArticle

Reactions of Substituted Furan-2-carboxaldehydes and Furo[b]pyrrole Type Aldehydes with Benzothiazolium Salts

1
Department of Chemistry, Faculty of Natural Sciences, University of St. Cyril and Methodius in Trnava, SK-917 01 Trnava, Slovak Republic
2
Research Institute for Organic Syntheses, Rybitvi 296, CZ-532 18 Pardubice 20, Czech Republic
*
Author to whom correspondence should be addressed.
Molecules 2004, 9(4), 241-255; https://doi.org/10.3390/90400241
Received: 18 February 2004 / Accepted: 23 March 2004 / Published: 31 March 2004

Abstract

A series of new push-pull compounds were synthesised by reaction of 5-aryl- furan-2-carboxaldehydes and furo[b]pyrrole type aldehydes with benzothiazolium salts. These new condensation products represent highly conjugated systems that have potential biological activity. The reaction of furo[b]pyrrole type aldehydes with benzothiazolium salts give potential precursors of cyanine dyes.
Keywords: 5-Arylfuran-2-carboxaldehydes; 2-formylfuro[3; 2-b]pyrrole-5-carboxylates; 2-formylfuro[2; 3-b]pyrrole-5-carboxylate; benzothiazolium salts; 1H- and 13C-NMR spectra. 5-Arylfuran-2-carboxaldehydes; 2-formylfuro[3; 2-b]pyrrole-5-carboxylates; 2-formylfuro[2; 3-b]pyrrole-5-carboxylate; benzothiazolium salts; 1H- and 13C-NMR spectra.

Introduction

Many compounds containing the benzothiazole moiety are reported to be biologically active and good structure-activity relations have been found using QSAR studies [1,2]. High antimicrobial activity of benzothiazolium salts has been reported for systems bearing electron-donating substituents at C2 and the activity increases if the substituent is bound by a conjugated polyene bridge [3]. The push-pull system is responsible for the high biological activity observed in these compounds. It has also been reported that these compounds can also be used as precursors of cyanine dyes [4].
In the past we have been interested in the synthesis and reactions of 5-arylfuran-2-carboxaldehydes 1 [5]. Many of the published condensation products of 5-arylfuran-2-carboxaldehydes are also reported to be biologically active compounds [6,7] or can be used as intermediates in organic synthesis [8,9]. Furo[b]pyrrole type aldehydes 2 and 3 are heteroanalogues of the pentalene dianion [10]. Their full synthesis and properties were described recently [11]. Only a few condensation products of furo[b]pyrrole type aldehydes have been described [12,13]. We have recently published in this journal the results of the study of the reactions of substituted furan-2-carboxaldehydes and furo[b]pyrrole type aldehydes with hippuric acid [14].
To the best of our knowledge 5-arylfuran-2-carboxaldehydes 1a-h, furo[3,2-b]pyrrole type aldehydes 2 and furo[2,3-b]pyrrole type aldehyde 3 have never been used in reactions with benzothiazolium salts. This fact has prompted us to synthesise a series of new condensation products of 5-arylfuran-2-carboxaldehydes 1a-h with 2,3-dimethyl-benzothiazolium iodide (4a), 3-ethyl-2-methylbenzothiazolium iodide (4b) and 3-benzyl-2-methylbenzothiazolium bromide (4c) under Knoevenagel reaction conditions. In this way we have obtained new highly conjugated systems 5a-7h containing furan and benzothiazole rings with potential biological activity. Further, we also describe condensation products of methyl 2-formyl-4H-furo[3,2-b]pyrrole-5-carboxylate (2a) with 2,3-dimethylbenzothiazolium iodide (4a) and 3-benzyl-2-methylbenzothiazolium bromide (4c). The 4-R derivatives 2b-d and methyl 2-formyl-6-methoxymethylfuro[2,3-b]pyrrole-5-carboxylate (3) were reacted with 3-benzyl-2-methylbenzothiazolium bromide (4c) to obtain a series of new condensation products 8a-d and 9. We have thus prepared 28 new compounds with predictable biological activity containing benzothiazole and substituted furan moieties. The structures of the products are fully supported by spectral data.

Results and Discussion

The reactions of 5-arylfuran-2-carboxaldehydes 1a-h with benzothiazolium salts 4 were carried out under various conditions. In the first case (Method A) acetonitrile was used as solvent and potassium acetate as support/catalyst in the reaction of 5-arylfuran-2-carboxaldehydes 1a-h with benzothiazolium salts 4a,b, as shown in Scheme 1 [19].
Scheme 1.
Scheme 1.
Molecules 09 00241 g001
The products 5a-6h were obtained in 37-88% yield. The yield of the final product was dependent on the benzene ring substitution of the starting aldehydes 1a-h. The lowest yields were obtained when the reaction was carried out with 1e and 1g, which possess ortho-substituents on the benzene ring. The highest yield was obtained with compound 1c having a 4-nitrophenyl group at the C5 position of the furan ring. A disadvantage of this procedure was the low solubility of the starting compounds in the acetonitrile which leads to low yields of the condensation products and in some cases the unreacted starting material was isolated along with the products. The condensation products had to be separated from the crude reaction mixtures by crystallisation and recrystallised to remove the starting material and thus give analytically pure compounds. Due to this experimental observation, for the subsequent reactions of compounds 1a-h with 3-benzyl-2-methylbenzothiazolium bromide (4c) we changed the reaction conditions.
Scheme 2.
Scheme 2.
Molecules 09 00241 g002
The published conditions using methanol as solvent and pyridine as catalyst (Method B) for the reactions shown in Scheme 2 was used [1,2]. With this procedure, products 7a-h were obtained as analytically pure compounds directly from the reaction mixtures in higher yields (43-91%). The same situation as in the reaction with acetonitrile was observed. Ortho-substituted benzene rings in the starting 5-arylfuran-2-carboxaldehydes 1e, 1g, 1h gave the lowest yields of products (~50%) and the 5-arylfuran-2-carboxaldehydes 1a-c with para-substituted benzene rings gave the highest yields of products (~80%). The condensations of furo[b]pyrrole type aldehydes 2 and 3 with benzothiazolium salts 4a,c lead to the corresponding products 8a-d and 9 in satisfactory yields (~40-60%) (Scheme 3, Scheme 4). The reactions were carried out in refluxing methanol with pyridine as catalyst. The character of furo[b]pyrrole type aldehydes [11] causes lower reactivity of carbonyl group in the C2 position in condensation reaction than is the case for 5-arylfuran-2-carboxaldehydes where the carbonyl group at C2 of the furan ring is activated by a benzene ring substituent in the C5 position.
Scheme 3.
Scheme 3.
Molecules 09 00241 g003
Scheme 4.
Scheme 4.
Molecules 09 00241 g004
All the condensation products are high melting stable solids that are sparingly soluble in common solvents. They are characterised by their colour. The absorption maximum appears in the VIS spectrum around 460 - 470 nm 5a-7h and 480 - 500 nm 8a-d and 9.
The 1H- and 13C-NMR spectral data of all synthesised products are collated in the Experimental section. The 1H-NMR spectra of the synthesised compounds display doublets for double bond protons in the 7.50-7.70 ppm region for H-α and 8.10-8.20 ppm for H-β, respectively. The coupling constants of the H-α and H-β protons are 15.2-15.5 Hz, which proves the E configurations of the condensation products. In the 13C-NMR spectra the chemical shifts for the C-α double bond carbons are observed at 110-111 ppm and C-β at 133-135 ppm. The chemical shifts of protons were assigned using gs-H,H-COSY (gradient selected Correlated Spectroscopy) measurements which provided the proton-proton connectivity. 13C-NMR chemical shift assignments were straightforward using gs-HSQC (gradient selected Heteronuclear Quantum Coherence) and gs-HMBC (gradient selected Heteronuclear Multiple Bond Correlation).

Conclusions

The syntheses of 3-methyl-2-[(E)-2-(5-arylfuran-2-yl)vinyl]-1,3-benzothiazolium iodides (5a-h), 3-ethyl-2-[(E)-2-(5-arylfuran-2-yl)vinyl]-1,3-benzothiazolium iodides (6a-h), 3-benzyl-2-{(E)-2-[(E)-2-(5-arylfuran-2-yl)vinyl]-1,3-benzothiazolium bromides (7a-h), 2-{(E)-2-[5-(methoxycarbonyl)-4H-furo[3,2-b]pyrrol-2-yl]vinyl}-3-methyl-1,3-benzothiazolium iodide (8a), 3-benzyl-2-{(E)-2-[5-(ethoxy / methoxycarbonyl)- 4H-, 4-methyl and 4-benzylfuro[3,2-b]pyrrol-2-yl]vinyl}-1,3-benzothiazolium bromides (8b-d) and 3-benzyl-2-{(E)-2-[5-(methoxycarbonyl)-6-methoxymethylfuro[2,3-b]pyrrol-2-yl]vinyl}-1,3-benzothiazolium bromide (9) are described. All synthesised compounds were characterised by spectroscopic measurements and were shown to be the pure E isomers.

Experimental

General

The compounds 1a-h were prepared according to references [15,16]. Furo[3,2-b]pyrrole type aldehydes 2 and 3 were prepared according to the literature [12,17,18]. Benzothiazolium salts 4a-c were prepared according to reference [19]. Melting points were determined using a Kofler hotplate apparatus and are uncorrected. All solvents were pre-distilled and dried appropriately prior to use. Concentration and evaporation refer to the removal of volatile materials under reduced pressure using a Büchi Rotovapor. Substances stated to be identical were so with respect to m.p.s, mixed m.p.s and IR spectra. Elemental analyses were determined using a Carlo Erba CHNS-OEA 1108-Elemental Analyser. UV spectra were measured on WPA UV/VIS Diode-Array spectrophotometer (Cambridge, UK) in methanol (λmax (log ε); λmax in nm, ε in m2mol-1). 1H and 13C NMR spectra were obtained using for: 5a-h, 6a-h BRUKER B-ACS (400 and 100 MHz), 5e BRUKER AMX (360 and 90 MHz), 7d-h VARIAN VRX (300 MHz, 75 MHz), 7a-c, 8a-d and 9 BRUKER AVANCE (500 MHz, 125 MHz) in DMSO-d6 with TMS as an internal standard reference. The methods used for the purpose of NMR assignment were gs-H,H-COSY, gs-HSQC and gs-HMBC. Coupling constants (J) are quoted to the nearest 0.3 Hz. Chemical shifts (δ-scale) are quoted in parts per million and the following abbreviations are used: s = singlet; d = doublet; t = triplet; q = quartet; m = multiplet; br = broad.

General procedures for synthesis of the condensation products.

Method A: A mixture of 5-arylfuran-2-carboxaldehyde 1a-h (2 mmol), benzothiazolium salt 4a,b (2.4 mmol) and a catalytic amount of potassium acetate (0.2 mmol) in dry acetonitrile (10-15 mL) was refluxed with stirring 1-5 h (monitored by TLC using 4:1 chloroform-methanol). After cooling down to room temperature the solid product was separated by filtration, washed with acetonitrile and methanol, dried and purified by crystallisation. Products 5a-6h were prepared using this method.
Method B: A mixture of 5-arylfuran-2-carboxaldehyde 1a-h (2 mmol) or furo[b]type aldehyde 2 or 3 (2 mmol) and benzothiazolium salt 3a,c (2.4 mmol) in methanol (15 mL) was refluxed for 1-4 h in the presence of a catalytic amount of pyridine (15 mg). Reactions were monitored by TLC (4:1 chloroform-methanol). After cooling down to room temperature the solid product was separated by filtration, washed with methanol and dried. Products 7a-9 were prepared by this procedure.
2-{(E)-2-[5-(4-Chlorophenyl)furan-2-yl]vinyl}-3-methyl-1,3-benzothiazolium iodide (5a). Reaction time: 85 min; yield 57%; m.p. 249-254°C (methanol); Calc. for C20H15ClINOS (479.76): 50.07% C, 3.15% H, 7.39% Cl, 2.92% N, 6.68% S; found: 50.22% C, 3.12% H, 7.43% Cl, 2.89% N, 6.71% S; UV: 463 (3.32); 1H-NMR (400 MHz): 8.42 (d, 1H, J(4,5) = 8.1 Hz, H-4), 8.24 (d, 1H, J(6,7) = 8.4 Hz, H-7), 8.08 (d, 2H, J(2´´,3´´) = 8.5 Hz, H-2´´, H-6´´), 8.12 (d, 1H, J(α,β) = 15.6 Hz, H-β), 7.87 (t, 1H, J(4,5) = 8.1 Hz, J(5,6) = 8.3 Hz, H-6), 7.78 (t, 1H, J(5,6) = 8.3 Hz, J(6.7) = 8.4 Hz, H-5), 7.74 (d, 1H, J(α,β) = 15.6 Hz, H-α), 7.61 (d, 2H, J(2´´,3´´) = 8.5 Hz, H-3´´, H-5´´), 7.47 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.43 (d, 1H, J(3´,4´ ) = 3.7 Hz, H-4´), 4.36 (s, 3H, N+CH3); 13C-NMR (100 MHz): 170.9 (C-2), 157.0 (C-5´), 150.5 (C-2´), 142.1 (C-3a), 134.1 (C-4´´), 133.1 (C-β), 129.3 (C-6), 129.2 (C-2´´), 128.2 (C-5), 127.6 (C-7a), 127.5 (C-1´´), 126.7 (C-3´´), 124.2 (C-7), 123.7 (C-3´), 116.7 (C-4), 111.1 (C-4´), 110.1 (C-α), 36.2 (N+CH3).
2-{(E)-2-[5-(4-Bromophenyl)furan-2-yl]vinyl}-3-methyl-1,3-benzothiazolium iodide (5b). Reaction time: 160 min; yield 57%; m.p. 255-258°C (ethanol); Calc. for C20H15BrINOS (524.21): 45.82% C, 2.88% H, 15.24% Br, 2.67% N, 6.12% S; found: 46.05% C, 2.92% H, 15.19% Br, 2.62% N, 6.17% S; UV: 463 (3.69); 1H-NMR (400 MHz): 8.42 (d, 1H, J(4,5) = 8.0 Hz, H-4), 8.24 (d, 1H, J(6,7) = 8.4 Hz, H-7), 8.00 (d, 2H, J(2´´,3´´) = 8.4 Hz, H-2´´, H-6´´), 8.11 (d, 1H, J(α,β) = 15.2 Hz, H-β), 7.87 (t, 1H, J(5,6) = 7.8 Hz, J(6,7) = 8.4 Hz, H-6), 7.78 (t, 1H, J(4,5) = 8.0 Hz, J(5,6) = 8.3 Hz, H-5), 7.73 (d, 1H, J(α,β) = 15.2 Hz, H-α), 7.73 (d, 2H, J(2´´,3´´) = 8.4 Hz, H-3´´, H-5´´), 7.47 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.43 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 4.37 (s, 3H, N+CH3); 13C-NMR (100 MHz): 170.9 (C-2), 157.1 (C-5´), 150.5 (C-2´), 142.0 (C-3a), 132.1 (C-2´´), 133.1 (C-β), 129.3 (C-6), 128.2 (C-5), 127.8 (C-4´´), 127.6 (C-7a), 126.8 (C-3´´), 124.2 (C-7), 122.9 (C-1´´), 123.7 (C-3´), 116.6 (C-4), 111.1 (C-4´), 110.1 (C-α), 36.3 (N+CH3).
3-Methyl-2-{(E)-2-[5-(4-nitrophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium iodide (5c). Reaction time: 270 min; yield 84%; m.p. 242-246°C (ethanol); Calc. for C20H15IN2O3S (490.32): 48.99% C, 3.08% H, 5.71% N, 6.54% S; found: 49.38% C, 3.14% H, 5.91% N, 6.61% S; UV: 453 (3.64); 1H-NMR (400 MHz): 8.44 (d, 1H, J(4,5) = 8.0 Hz, H-4), 8.37 (d, 2H, J(2´´,3´´) = 8.0 Hz, H-3´´, H-5´´), 8.30 (d, 2H, J(2´´,3´´) = 8.0 Hz, H-2´´, H-6´´), 8.27 (d, 1H, J(6,7) = 8.7 Hz, H-7), 8.16 (d, 1H, J(α,β) = 15.6 Hz, H-β), 7.89 (t, 1H, J(4,5) = 8.0 Hz, J(5,6) = 7.7 Hz, H-6), 7.85 (d, 1H, J(α,β) = 15.6 Hz, H-α), 7.80 (t, 1H, J(5,6) = 7.7 Hz, J(6,7) = 8.7 Hz, H-5), 7.66 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.52 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 4.37 (s, 3H, N+CH3); 13C-NMR (100 MHz): 171.4 (C-2), 156.0 (C-5´), 152.4 (C-2´), 147.1 (C-1´´), 142.7 (C-3a), 135.0 (C-4´´), 133.5 (C-β), 130.1 (C-6), 129.0 (C-5), 128.5 (C-7a), 126.3 (C-3´´), 125.0 (C-2´´), 124.9 (C-7), 123.6 (C-3´), 117.0 (C-4), 114.5 (C-4´), 112.2 (C-α), 37.0 (N+CH3).
3-Methyl-2-{(E)-2-[5-(3-nitrophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium iodide (5d). Reaction time: 120 min; yield 82%; m.p. 220-224°C (ethanol); Calc. for C20H15IN2O3S (490.32): 48.99% C, 3.08% H, 5.71% N, 6.54% S; found: 49.26% C, 3.21% H, 5.87% N, 6.65% S; UV: 449 (3.36); 1H-NMR (400 MHz): 8.76 (s, 1H, H-2´´), 8.49 (d, 1H, J(4,5) = 8.0 Hz, H-4), 8.43 (d, 1H, J(5´´,6´´) = 8.1 Hz, H-6´´), 8.27 (d, 1H, J(6,7) = 8.0 Hz, H-7), 8.26 (d, 1H, J(4´´,5´´) = 8.2 Hz, H-4´´), 8.1 (d, 1H, J(α,β) = 15.5 Hz, H-β), 7.88 (t, 1H, , J(4,5) = 8.0 Hz, J(5,6) = 7.5 Hz, H-6), 7.83 (t, 1H, J(4´´,5´´) = 8.2 Hz, J(5´´,6´´) = 8.1 Hz, H-5´´), 7.83 (d, 1H, J(α,β) = 15.5 Hz, H-α), 7.79 (t, 1H, J(5,6) = 7.5 Hz, J(6,7) = 8.0 Hz, H-5), 7.65 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´ ), 7.51 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 4.38 (s, 3H, N+CH3); 13C-NMR (100 MHz): 170.8 (C-2), 155.3 (C-5´), 151.0 (C-2´), 148.5 (C-3´´), 141.9 (C-3a), 132.9 (C-β), 130.7 (C-6´´), 130.6 (C-4´´), 130.1 (C-1´´), 129.3 (C-6), 128.2 (C-5), 127.7 (C-7a), 124.9 (C-7), 124.1 (C-5´´), 122.9 (C-3´), 116.6 (C-4), 119 (C-2´´), 112.3 (C-4´), 111 (C-α), 36.2 (N+CH3).
3-Methyl-2-{(E)-2-[5-(2-nitrophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium iodide (5e). Reaction time: 7 hours (synthesised without using a catalyst); yield 37%; m.p. 240-243°C (ethanol); Calc. for C20H15IN2O3S (490.32): 48.99% C, 3.08% H, 5.71% N, 6.54% S; found: 48.66% C, 3.19% H, 5.82% N, 6.48% S; UV: 439 (3.49); 1H-NMR (360 MHz): 8.43 (d, 1H, J(4,5) = 8.7 Hz, H-4), 8.25 (d, 1H, J(6,7) = 8.6 Hz, H-7 ), 8.12 (d, 1H, J(α,β) = 15.5 Hz, H-β ), 8.1 (d, 1H, J(5´´,6´´) = 7.9 Hz, H-6´´), 8.02 (d, 1H, J(3´´,4´´) = 8.1 Hz, H-3´´), 7.85 (t, 1H, J(4,5) = 8.7 Hz, J(5,6) = 7.7 Hz, H-6), 7.84 (t, 1H, J(4´´,5´´) = 8.6 Hz, J(5´´,6´´) = 7.9 Hz, H-5´´), 7.74 (t, 1H, J(3´´,4´´) = 8.1 Hz, J(4´´,5´´) = 8.6 Hz, H-4´´), 7,70 (t, J(5,6) = 7.7 Hz, J(6,7) = 8.6 Hz, 1H, H-5), 7.51 (d, 1H, J(α,β) = 15.5 Hz, H-α), 7.48 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.22 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 4,30 (s, 3H, N+CH3); 13C-NMR (100 MHz): 171 (C-2), 152.9 (C-5´), 151.8 (C-2´), 147.7 (C-2´´), 142.4 (C-3a), 133.3 (C-β), 133.3 (C-5´´), 131.3 (C-4´´), 130.1 (C-6´´), 129.9 (C-6), 128.9 (C-5), 128.3 (C-7a), 124.8 (C-3´´), 124.7 (C-7), 122.5 (C-3´), 122 (C-1´´), 117.2 (C-4), 114.3 (C-4´), 111.5 (C-α), 36.3 (N+CH3).
3-Methyl-2-((E)-2-{5-[3-(trifluoromethyl)phenyl]furan-2-yl}vinyl)-1,3-benzothiazolium iodide (5f). Reaction time: 150 min; yield 46%; m.p. 242-246°C (methanol); Calc. for C21H15F3INOS (513.32): 49.14% C, 2.95% H, 2.73% N, 6.25% S; found: 49.30% C, 3.01% H, 2.69% N, 6.22% S; UV: 449 (3.32); 1H-NMR (400 MHz): 8.52 (d, 1H, J(4,5) = 8.0 Hz, H-4), 8.29 (d, 1H, J(5´´,6´´) = 8.2 Hz, H-6´´), 8.33 (s, 1H, H-2´´), 8.26 (d, 1H, J(6,7) = 8.2 Hz, H-7), 8.17 (d, 1H, J(α,β) = 15.4 Hz, H-β ), 7.85 (t, 1H, J(4,5) = 8.0 Hz, J(5,6) = 8.0 Hz, H-6), 7.82 (t, 1H, J(5,6) = 8.0 Hz, J(6,7) = 8.2 Hz, H-5 ), 7.76 (d, 1H, J(4´´,5´´) = 7.9 Hz, H-4´´), 7,72 (d, 1H, J(α,β) = 15.4 Hz, H-α) 7.69 (t, 1H, J(4´´,5´´) = 7.9 Hz, J(5´´,6´´) = 8.2 Hz, H-5´´), 7.59 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.55 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 4.50 (s, 3H, N+CH3); 13C-NMR (100 MHz): 171.4 (C-2), 155.8 (C-5´), 151.0 (C-2´), 143.2 (C-3a), 134.1 (C-β), 130.9 (C-5´´), 130.1 (CF3), 129.5 (C-6), 128.9 (C-6´´), 128.1 (C-5), 127.9 (C-7a), 126.1 (C-4´´), 124.8 (C-7), 123.7 (C-3´), 122.2 (C-1´´), 117.1 (C-4), 112.0 (C-4´), 110.5 (C-α), 37.1 (N+CH3).
2-{(E)-2-[5-(2-Bromophenyl)furan-2-yl]vinyl}-3-methyl-1,3-benzothiazolium iodide (5g). Reaction time: 60 min; yield 60%; m.p. 215-219°C (ethanol); Calc. for C20H15BrINOS (524.21): 45.82% C, 2.88% H, 15.24% Br, 2.67% N, 6.12% S; found: 45.96% C, 2.79% H, 15.31% Br, 2.59% N, 6.20% S; UV: 449 (3.44); 1H-NMR (400 MHz): 8.62 (d, 1H, J(4,5) = 8.0 Hz, H-4), 8.44 (d, 1H, J(6,7) = 8.0 Hz, H-7 ), 8.35 (d, 1H, J(5´´,6´´) = 7.8 Hz, H-6´´), 8.33 (d, 1H, J(α,β) = 15.5 Hz, H-β), 8.06 (d, 1H, J(4´´,5´´) = 7.7 Hz, H-5´´), 7.97 (t, 1H, J(3´´,4´´) = 8.0 Hz, J(4´´,5´´) = 7.7 Hz, H-4´´), 7.90 (d, 1H, J(α,β) = 15.5 Hz, H-α), 7.77 (t, 1H, J(4,5) = 8.4 Hz, J(5,6) = 7.7 Hz, H-6), 7.72 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.69 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 7.59 (t, 1H, J(5,6) = 7.7 Hz, J(6,7) = 8.0 Hz, H-5) 4.53 (s, 3H, N+CH3); 13C-NMR (100 MHz): 171.2 (C-2), 155.6 (C-5´), 150.7 (C-2´), 142.4 (C-3a), 134.9 (C-β), 133.5 (C-5´´), 131.3 (C-4´´), 130.3 (C-6´´), 129.8 (C-6), 129.4 (C-2´´), 128.7 (C-3´´), 128.6 (C-5), 128.1 (C-7a), 123.5 (C-7), 122.9 (C-3´), 120 (C-1´´), 117.1 (C-4), 114.3 (C-4´), 111.2 (C-α), 36.7 (N+CH3).
2-{(E)-2-[5-(2,4-Dichlorophenyl)furan-2-yl]vinyl}-3-methyl-1,3-benzothiazolium iodide (5h). Reaction time: 60 min; yield: 86 %; m.p. 248-253°C (ethanol); Calc. for C20H14Cl2INOS (514.21): 46.72% C, 2.74% H, 13.79% Cl, 24.68% I, 2.72% N, 3.11% O, 6.24% S; found: 46.72% C, 2.74% H, 13.79% Cl, 2.72% N, 6.24% S; UV: 449 (3.59); 1H-NMR (400 MHz): 8.35 (d, 1H, J(4,5) = 8.4 Hz, H-4), 8.30 (d, 1H, J(5´´,6´´) = 8.6 Hz, H-6´´ ), 8.25 (d, 1H, J(6,7) = 8.0 Hz, H-7 ), 8.15 (d, 1H, J(α,β) = 15.5 Hz, H-β), 7.88 (t, 1H, J(4,5) = 8.4 Hz, J(5,6) = 7.6 Hz, H-6), 7.84 (s, 1H, H-3´´), 7.79 (t, 1H, J(5,6) = 7.6 Hz, J(6,7) = 8.0 Hz, H-5), 7.77 (d, 1H, J(α,β) = 15.5 Hz, H-α), 7.64 (d, 1H, J(5´´,6´´) = 8.6 Hz, H-5´´), 7.53 (d, 1H, J(3´,4´) = 3.8 Hz, H-3´), 7.50 (d, 1H, J(3´,4´) = 3.8 Hz, H-4´), 4.36 (s, 3H, N+CH3); 13C-NMR (100 MHz): 170.7 (C-2), 152.6 (C-5´), 150.2 (C-2´), 141.9 (C-3a), 134.1 (C-4´´), 132.8 (C-β), 130.7 (C-2´´), 130.4 (C-5´´), 130 (C-3´´), 129.3 (C-6), 128.2 (C-6´´), 127.8 (C-5), 127.7 (C-7a), 125.8 (C-1´´), 124.1 (C-7), 122.5 (C-3´), 116.6 (C-4), 115.5 (C-4´), 111.1 (C-α), 36.2 (N+CH3).
2-{(E)-2-[5-(4-Chlorophenyl)furan-2-yl]vinyl}-3-ethyl-1,3-benzothiazolium iodide (6a). Reaction time: 150 min; yield 62%; m.p. 245-246°C (methanol); Cal. for C21H17ClINOS (493.79): 51.08% C, 3.47% H, 7.18% Cl, 2.84% N, 6.49% S; found: 51.74% C, 3.55% H, 7.21% Cl, 2.79% N, 6.53% S; UV 468 (3.61); 1H-NMR (400 MHz): 8.43 (d, 1H, J(4,5) = 8.0 Hz, H-4), 8.28 (d, 1H, J(6,7) = 8.5 Hz, H-7), 8.07 (d, 2H, J(2´´,3´´) = 8.6 Hz, H-2´´, H-6´´), 8.14 (d, 1H, J(α,β) = 15.4 Hz, H-β), 7.87 (t, 1H, J(4,5) = 8.0 Hz, J(5,6) = 7.8 Hz, H-6), 7.78 (t, 1H, J(5,6) = 7.8 Hz, J(6,7) = 8.5 Hz, H-5), 7.71 (d, 1H, J(α,β) = 15.4 Hz, H-α), 7.61 (d, 2H, J(2´´,3´´) = 8.6 Hz, H-3´´, H-5´´), 7.50 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.43 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 4.97 (q, 2H, N+CH2), 1.49 (t, 3H, CH3); 13C-NMR (100 MHz): 171.4 (C-2), 158.1 (C-5´), 151.4 (C-2´), 141.9 (C-3a), 135.1 (C-4´´), 134.6 (C-β), 130.4 (C-6), 130.1 (C-2´´), 129.2 (C-5), 129 (C-7a), 128.4 (C-1´´), 127.7 (C-3´´), 125.4 (C-7), 124.8 (C-3´), 117 (C-4), 112.1 (C-4´), 110.2 (C-α), 45.3 (N+CH2), 15.1 (CH3).
2-{(E)-2-[5-(4-Bromophenyl)furan-2-yl]vinyl}-3-ethyl-1,3-benzothiazolium iodide (6b). Reaction time: 180 min; yield 45 %; m.p. 248-249°C (methanol); Calc. for C21H17BrINOS (538.24): 46.86% C, 3.18% H, 14.85% Br, 2.60% N, 5.96% S; found: 46.80% C, 3.08% H, 14.69% Br, 2.62% N, 5.82% S; UV 468 (3.61); 1H-NMR (400 MHz): 8.43 (d, 1H, J(4,5) = 8.0 Hz, H-4), 8.27 (d, 1H, J(6,7) = 8.4 Hz, H-7), 7.98 (d, 2H, J(2´´,3´´) = 8.6 Hz, H-2´´, H-6´´), 8.11 (d, 1H, J(α,β) = 15.4 Hz, H-β), 7.85 (t, 1H, J(5,6) = 7.8 Hz, J(6,7) = 8.4 Hz, H-6), 7.76 (t, 1H, J(4,5) = 8.0 Hz, J(5,6) = 7.8 Hz, H-5), 7.71 (d, 1H, J(α,β) = 15.4 Hz, H-α), 7.70 (d, 2H, J(2´´,3´´) = 8.6 Hz, H-3´´, H-5´´), 7.49 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.43 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 4.98 (q, 2H, N+CH2), 1,47 (t, 3H, CH3); 13C-NMR (100 MHz): 171.5 (C-2), 158.1 (C-5´), 151.5 (C-2´), 141.9 (C-3a), 134.6 (C-β), 133.0 (C-2´´), 130.4 (C-6), 129.2 (C-5), 129 (C-7a), 128.7 (C-4´´), 127.9 (C-3´´), 125.4 (C-7), 124.8 (C-3´), 123.8 (C-1´´), 117.4 (C-4), 112.1 (C-4´), 110.3 (C-α), 45.3 (N+CH2), 15.1 (CH3).
3-Ethyl-2-{(E)-2-[5-(4-nitrophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium iodide (6c). Reaction time: 220 min; yield 79%; m.p. 265-268°C (ethanol); Calc. for C21H17IN2O3S (504.34): 50.01% C, 3.40% H, 5.55% N, 6.36% S; found: 50.08% C, 3.45% H, 5.61% N, 6.42% S; UV: 458 (3.57); 1H-NMR (400 MHz): 8.46 (d, 1H, J(4,5) = 8.9 Hz, H-4), 8.35 (d, 2H, J(2´´,3´´) = 8.9 Hz, H-3´´, H-5´´), 8.29 (d, 2H, J(2´´,3´´) = 8.9 Hz, H-2´´, H-6´´), 8.29 (d, 1H, J(6,7) = 8.9 Hz, H-7), 8.17 (d, 1H, J(α,β) = 15.5 Hz, H-β), 7.88 (t, 1H, J(4,5) = 8.9 Hz, J(5,6) 7.6 Hz, H-6), 7.80 (t, 1H, J(5,6) = 7.6 Hz, J(6,7) = 8.9 Hz, H-5), 7.71 (d, 1H, J(α,β) = 15.5 Hz, H-α), 7.66 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.55 (d, 1H, J(3´,4´) = 3.7Hz, H-4´), 5.01 (q, 2H, N+CH2), 1.51 (t, 3H, CH3); 13C-NMR (100 MHz): 170.3 (C-2), 155.3 (C-5´), 151.6 (C-2´), 146.9 (C-1´´), 142.8 (C-3a), 134.1 (C-4´´), 133.3 (C-β), 129.5 (C-6), 128.3 (C-5), 128.2 (C-7a), 125.6 (C-3´´), 124.3 (C-2´´), 124.3 (C-7), 123.1 (C-3´), 116.5 (C-4), 113.7 (C-4´), 110.7 (C-α), 44.4 (N+CH2), 14.1 (CH3).
3-Ethyl-2-{(E)-2-[5-(3-nitrophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium iodide (6d). Reaction time: 90 min; yield 74%; m.p. 246-248°C (ethanol); Calc. for C21H17IN2O3S (504.34): 50.01% C, 3.40% H, 5.55% N, 6.36% S; found: 49.89% C, 3.35% H, 5.48% N, 6.41% S; UV: 449 (3.36); 1H-NMR (400 MHz): 8.75 (s, 1H, H-2´´), 8.49 (d, 1H, J(4,5) = 8.0 Hz, H-4), 8.43 (d, 1H, J(5´´,6´´) = 8.0 Hz, H-6´´), 8.31 (d, 1H, J(4´´,5´´) = 7.9 Hz, H-4´´), 8.27 (d, 1H, J(6,7) = 8.5 Hz, H-7), 8.2 (d, 1H, J(α,β) = 15.4 Hz, H-β), 7.88 (t, 1H, J(4,5) = 8.0 Hz, J(5,6) = 7.7 Hz, H-6), 7.85 (t, 1H, J(4´´,5´´) = 7.9 Hz, J(5´´,6´´) = 8.0 Hz, H-5´´), 7.80 (d, 1H, J(α,β) = 15.4 Hz, H-α), 7.80 (t, 1H, J(5,6) = 7.7 Hz, J(6,7) = 8.5 Hz, H-5), 7.66 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.55 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 4.99 (q, 2H, N+CH2), 1.51 (t, 3H, CH3); 13C-NMR (100 MHz): 170.5 (C-2), 155.4 (C-5´), 151.0 (C-2´), 148.5 (C-3´´), 140.8 (C-3a), 133.5 (C-β), 130.7 (C-4´´), 130.6 (C-1´´), 129.4 (C-6), 128.2 (C-5), 128.1 (C-7a), 124.3 (C-5´´), 123.5 (C-7), 123.0 (C-3´´), 119.0 (C-2´´), 116.5 (C-4), 112.4 (C-4´), 110.7 (C-α), 44.3 (N+CH2), 14.0 (CH3).
3-Ethyl-2-{(E)-2-[5-(2-nitrophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium iodide (6e). Reaction time: 190 min; yield 46%; m.p. 227-231°C (ethanol); Calc. for C21H17IN2O3S (504.34): 50.01% C, 3.40% H, 5.55% N, 6.36% S; found: 50.21% C, 3.42% H, 5.61% N, 6.41% S; UV: 439 (3.47); 1H-NMR (400 MHz): 8.45 (d, 1H, J(4,5) = 8.0 Hz, H-4), 8.32 (d, 1H, J(6,7) = 8.4 Hz, H-7 ), 8.16 (d, 1H, J(α,β) = 15.5 Hz, H-β ), 8.1 (d, 1H, J(5´´,6´´) = 7.7 Hz, H-6´´), 8.01 (d, 1H, J(3´´,4´´) = 7.9 Hz, H-3´´), 7.88 (t, 1H, J(4,5) = 8.0 Hz, J(5,6) = 7.7 Hz, H-6), 7.84 (t, 1H, J(4´´,5´´) = 8.8 Hz, J(5´´,6´´) = 7.7 Hz, H-5´´), 7.80 (t, 1H, J(3´´,4´´) = 7.8 Hz, J(4´´,5´´) = 8.8 Hz, H-4´´), 7.72 (t, J(5,6) = 7.7 Hz, J(6,7) = 8.4 Hz, 1H, H-5), 7.50 (d, 1H, J(α,β) = 15.5 Hz, H-α), 7.50 (d, 1H, J(3´,4´) = 3.7, H-3´), 7.29 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 5.01(q, 2H, N+CH2), 1.51 (t, 3H, CH3); 13C-NMR (100 MHz): 169.9 (C-2), 152.3 (C-5´), 151.2 (C-2´), 147.1 (C-2´´), 140.8 (C-3a), 133.1 (C-β), 132.5 (C-5´´), 130.7 (C-4´´), 129.5 (C-6), 129.2 (C-6´´), 128.3 (C-5), 128.2 (C-7a), 124.4 (C-3´´), 124.0 (C-7), 122.0 (C-3´), 121.2 (C-1´´), 116.4 (C-4), 113.6 (C-4´), 110.52 (C-α), 44.3 (N+CH2), 13.8 (CH3).
3-Ethyl-2-((E)-2-{5-[3-(trifluoromethyl)phenyl]furan-2-yl}vinyl)-1,3-benzothiazolium iodide (6f). Reaction time: 100 min; yield 58%; m.p. 170-174°C (methanol); Calc. for C22H17F3INOS (527.34): 50.11% C, 3.25% H, 2.66% N, 6.08% S; found: 50.22% C, 3.31% H, 2.72% N, 6.11% S; UV: 453 (3.24); 1H-NMR (400 MHz): 8.47 (d, 1H, J(4,5) = 8.0 Hz, H-4), 8.35 (d, 1H, J(5´´,6´´) = 7.6 Hz, H-6´´), 8.33 (s, 1H, H-2´´), 8.31 (d, 1H, J(6,7) = 8.7 Hz, H-7), 8.17 (d, 1H, J(α,β) = 15.2 Hz, H-β ), 7.85 (t, 1H, J(4,5) = 8.0 Hz, J(5,6) = 7.6 Hz, H-6), 7.8 (t, 1H, J(5,6) = 7.6 Hz, J(6,7) = 8.7 Hz, H-5), 7.78 (d, 1H, J(4´´,5´´) = 7.7 Hz, H-4´´), 7,78 (d, 1H, J(α,β) = 15.2 Hz, H-α) 7.77 (t, 1H, J(4´´,5´´) = 7.7 Hz, J(5´´,6´´) = 7.6 Hz, H-5´´), 7.61 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.55 (d, 1H, J(3´,4´ ) = 3.7 Hz, H-4´), 4.99 (q, 2H, N+CH2), 1.50 (t, 3H, CH3); 13C-NMR (100 MHz): 170.6 (C-2), 156.3 (C-5´), 150.9 (C-2´), 141.0 (C-3a), 133.7 (C-β), 130.3 (C-5´´), 129.9 (d, CF3), 129.5 (C-6), 128.6 (C-6´´), 128.3 (C-5), 128.2 (C-7a), 125.7 (C-4´´), 124.4 (C-7), 123.4 (C-3´), 122.6 (C-1´´), 116.5 (C-4), 112.0 (C-4´), 110.1 (C-α), 44.4 (N+CH2), 14.1 (CH3).
2-{(E)-2-[5-(2-Bromophenyl)furan-2-yl]vinyl}-3-ethyl-1,3-benzothiazolium iodide (6g). Reaction time: 90 min; yield 47 %; m.p. 235-237°C (methanol); Calc. for C21H17BrINOS (538.24); 46.86% C, 3.18% H, 15.24% Br, 2.67% N, 6.12% S; found: 46.95% C, 3.06% H, 15.32% Br, 2.74% N, 6.09% S; UV: 449 (3.65); 1H-NMR (400 MHz): 8.44 (d, 1H, J(4,5) = 7.9 Hz, H-4), 8.30 (d, 1H, J(6,7) = 8.4 Hz, H-7), 8.18 (d, 1H, J(α,β) = 15.5 Hz, H-β), 8.1 (d, 1H, J(5´´,6´´) = 7.9 Hz, H-6´´), 7.84 (t, 1H, J(4´´,5´´) = 7.6 Hz, J(5´´,6´´) = 7.9 Hz, H-5´´), 7.79 (t, 1H, J(3´´,4´´) = 8.0 Hz, J(4´´,5´´) 7.6 Hz, H-4´´), 7.70 (d, 1H, J(α,β) = 15.5 Hz, H-α), 7.59 (t, 1H, J(4,5) = 7.9 Hz, J(5,6) = 8.0 Hz, H-6), 7.40 (t, 1H, J(5,6) = 8.0 Hz, J(6,7) = 8.4 Hz, H-5), 7.55 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.52 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 4.96 (q, 2H, N+CH2), 1.49 (t, 3H, CH3); 13C-NMR (100 MHz): 171.0 (C-2), 155.7 (C-5´), 150.7 (C-2´), 141.3 (C-3a), 133.8 (C-β), 132.5 (C-5´´), 131.3 (C-4´´), 130.7 (C-6´´), 129.4 (C-6), 129.3 (C-2´´), 128.7 (C-3´´), 128.7 (C-7a), 128.6 (C-5), 124.8 (C-7), 122.9 (C-3´), 120.0 (C-1´´), 116.9 (C-4), 115.1 (C-4´), 110.5 (C-α), 44.8 (N+CH2), 14.5 (CH3).
2-{(E)-2-[5-(2,4-Dichlorophenyl)furan-2-yl]vinyl}-3-ethyl-1,3-benzothiazolium iodide (6h). Reaction time: 130 min; yield: 88 %, m.p. 260-263°C (methanol); Calc. for C21H16Cl2INOS (528.23): 47.75% C, 3.05% H, 13.42% Cl, 2.65% N, 6.07% S; found: 47.90% C, 3.15% H, 13.46% Cl, 2.71% N, 6.11% S; UV: 449 (3.59); 1H-NMR (400 MHz): 8.44 (d, 1H, J(4,5) = 8.1 Hz, H-4), 8.30 (d, 1H, J(6,7) = 8.5 Hz, H-7), 8.27 (d, 1H, J(5´´,6´´) = 8.8 Hz, H-6´´), 8.17 (d, 1H, J(α,β) = 15.5 Hz, H-β), 7.87 (t, 1H, J(4,5) = 8.1 Hz, J(5,6) = 7.7 Hz, H-6), 7.83 (s, 1H, H-3´´), 7.80 (t, 1H, J(5,6) = 7.7 Hz, J(6,7) = 8.5 Hz, H-5), 7.75 (d, 1H, J(α,β) = 15.5 Hz, H-α), 7.64 (d, 1H, J(5´´,6´´) = 8.8 Hz, H-5´´), 7.54 (br s, 2H, H-3´, H-4´), 4.99 (q, 2H, N+CH2), 1.48 (t, 3H, CH3); 13C-NMR (100 MHz): 170.4 (C-2), 152.9 (C-5´), 150.2 (C-2´), 140.8 (C-3a), 134.1 (C-4´´), 133.4 (C-β), 130.8 (C-2´´), 130.4 (C-5´´), 130.1 (C-3´´), 129.5 (C-6), 128.1 (C-6´´), 128.1 (C-7a), 127.9 (C-5), 125.9 (C-1´´), 124.3 (C-7), 122 (C-3´), 116.4 (C-4), 113.6 (C-4´), 110.5 (C-α), 44.3 (N+CH2), 14 (CH3).
3-Benzyl-2-{(E)-2-[5-(4-chlorophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium bromide (7a). Reaction time: 70 min; yield: 91%; m.p. 232-235°C; Calc. for C26H19BrClNOS (508.85): 61.37% C, 3.76% H, 15.70% Br, 6.97% Cl; found: 61.21% C, 3.63% H, 15.81% Br, 7.06% Cl; UV: 478 (3.96); 1H-NMR (500 MHz): 8.55(d, 1H, J(4,5) = 8.0 Hz, H-4), 8.24 (d, 1H, J(6,7) = 8.5 Hz, H-7), 8.00 (d, 2H, J(2´´,3´´) = 8.6 Hz, H-2´´, H-6´´), 8.26 (d, 1H, J(α,β) = 15.3 Hz, H-β), 7.82 (t, 1H, J(4,5) = 8.0 Hz, J(5,6) = 7.8 Hz, H-6), 7.84 (t, 1H, J(5,6) = 7.8 Hz, J(6,7) = 8.5 Hz, H-5), 7.93 (d, 1H, J(α,β) = 15.4 Hz, H-α), 7.63 (d, 2H, J(2´´,3´´) = 8.6 Hz, H-3´´, H-5´´), 7.58 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 7.47 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 6.34 (s, 2H, N+CH2Ph), 7.40-7.44 (m, 4H, ArH); 13C-NMR (125 MHz): 171.78 (C-2), 157.44 (C-5´), 150.59 (C-2´), 141.44 (C-3a), 134.29 (C-4´´), 134.25 (C-β), 129.64 (C-6), 129.26 (C-3´´), 128.13 (C-7a), 128.36 (C-5), 127.49 (C-1´´), 126.81 (C-2´´), 124.69 (C-4), 124.54 (C-4´), 116.89 (C-7), 111.38 (C-3´), 109.63 (C-α), 51.46 (N+CH2Ph), 134.15, 129.26, 128.61, 127.11.
3-Benzyl-2-{(E)-2-[5-(4-bromophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium bromide (7b). Reaction time: 100 min; yield: 87%; m.p. 225-228°C; Calc. for C26H18Br2NOS (553.31): 56.44% C, 3.46% H, 28.88% Br, 2.53% N, 5.80% S; found: 56.62% C, 3.35% H, 29.21% Br, 2.74% N, 6.12% S; UV: 478 (3.67); 1H-NMR (500 MHz): 8.55 (d, 1H, J(4,5) = 8.0 Hz, H-4), 8.23 (d, 1H, J(6,7) = 8.4 Hz, H-7), 8.32 (d, 1H, J(α,β) = 15.4 Hz, H-β), 8.00 (d, 2H, J(2´´,3´´) = 8.6 Hz, H-2´´, H-6´´), 7.86 (t, 1H, J(4,5) = 8.0 Hz, J(5,6) = 7.8 Hz, H-6), 7.82 (t, 1H, J(5,6) = 7.8 Hz, J(6,7) = 8.4 Hz, H-5), 7.79 (d, 2H, J(2´´,3´´) = 8.6 Hz, H-3´´, H-5´´), 7.71 (d, 1H, J(α,β) = 15.4 Hz, H-α), 7.56 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 7.48 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 6.34 (s, 2H, N+CH2Ph); 13C-NMR (125 MHz): 171.84 (C-2), 157.49 (C-5´), 150.59 (C-2´), 141.44 (C-3a), 134.26 (C-β), 132.27 (C-3´´), 129.67 (C-6), 128.64 (C-5), 128.13 (C-7a), 127.84 (C-1´´),127.11 (C-2´´), 124.65 (C-4), 124.50 (C-4´), 123.12 (C-4´´), 116.89 (C-7), 114.43 (C-3´), 109.68 (C-α), 51.48 (N+CH2Ph), 129.29, 128.72, 127.14.
3-Benzyl-2-{(E)-2-[5-(4-nitrophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium bromide (7c). Reaction time: 130 min; yield: 64%; m.p. 235-240°C; Calc. for C26H19BrN2O3S (519.41): 60.12% C, 3.69% H, 15.38% Br, 5.39% N, 6.17% S; found: 60.44% C, 3.45% H, 15.37% Br, 5.62% N, 6.22% S; UV: 463 (3.58); 1H-NMR (500 MHz): 8.54 (d, 1H, J(4,5) = 8.6 Hz, H-4), 8.40 (d, 2H, J(2´´,3´´) = 8.9 Hz, H-3´´, H-5´´), 8.31 (d, 2H, J(2´´,3´´) = 8.9 Hz, H-2´´, H-6´´), 8.27 (d, 1H, J(6,7) = 8.6 Hz, H-7), 8.32 (d, 1H, J(α,β) = 15.5 Hz, H-β), 7.88 (t, 1H, J(4,5) = 8.9 Hz, J(5,6) 7.6 Hz, H-5), 7.82 (t, 1H, J(5,6) = 7.6 Hz, J(6,7) = 8.6 Hz, H-6), 8.05 (d, 1H, J(α,β) = 15.5 Hz, H-α), 7.71 (d, 1H, J(3´,4´) = 3.7Hz, H-4´), 7.60 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 6.38 (s, 2H, N+CH2Ph); 13C-NMR (125 MHz): 171.85 (C-2), 155.78 (C-5´), 151.85 (C-2´), 147.27 (C-4´´), 141.48 (C-3a), 134.35 (C-1´´), 134.12 (C-β), 129.82 (C-6), 128.64 (C-5), 128.37 (C-7a), 125.84, (C-2´´), 124.77 (C-4), 124.59 (C-3´´), 117.09 (C-7), 123.85 (C-3´), 114.16 (C-4´), 111.2 (C-α), 51.66 (N+CH2Ph), 129.34, 128.72, 127.18.
3-Benzyl-2-{(E)-2-[5-(3-nitrophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium bromide (7d). Reaction time: 100 min; yield: 86%; m.p. 245-247°C; Calc. for C26H19BrN2O3S (519.41): 60.12% C, 3.69% H, 15.38% Br, 5.39% N, 6.17% S; found: 60.13% C, 3.52% H, 15.43% Br, 5.56% N, 6.24% S; UV: 458 (3.73); 1H-NMR (300 MHz): 8.74 (s, 1H, H-2´´), 8.50 (d, 1H, J(4,5) = 7.5 Hz, H-4), 8.44-8.48 (m, 3H, Harom), 8.27 (d, 1H, J(5´´,6´´) = 7.5 Hz, H-6´´), 8.26 (d, 1H, J(α,β) = 15.6 Hz, H-β), 7.94 (d, 1H, J(α,β) = 15.6 Hz, H-α ), 7.78-7.86 (m, 3H, Harom), 7.66 (d, 1H, J(3´,4´) = 3.6 Hz, H-3´), 7.42 (d, 1H, J(3´,4´) = 3.6 Hz, H-4´), 7.37 – 7.39 (m, 4H, Harom), 6.32 (s, 2H, CH2Ph); 13C-NMR (75 MHz): 171.65 (C-2), 155.64 (C-5´), 151.0 (C-2´), 148.55 (C-3´´), 141.37 (C-3a), 134.01 (C-β), 130.81 (C-6´´), 130.08 (C-4´´), 129.63 (C-1´´), 128.15 (C-6), 127.00 (C-7a), 124.56 (C-7), 123.73 (C-5´´), 123.65 (C-3´), 116.83 (C-4´), 110.56 (C-α), 51.4 (CH2Ph), 128.55, 128.40, 119.06.
3-Benzyl-2-{(E)-2-[5-(2-nitrophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium bromide (7e). Reaction time: 75 min; yield: 68%; m.p. 194-198°C; Calc. for C26H19BrN2O3S (519.41): 60.12% C, 3.69% H, 15.38% Br, 5.39% N, 6.17% S; found: 60.32% C, 3.65% H, 15.47% Br, 5.61% N, 6.14% S; UV: 449 (3.62); 1H-NMR (300 MHz): 8.49 (d, 1H, J(4,5) = 8.5 Hz, H-4), 8.31 (d, 1H, J(6,7) = 8.3 Hz, H-7), 8.21 – 8.29 (m, 5H, Harom), 8.19 (d, 1H, J(α,β) = 15.5 Hz, H-β), 7.98 – 8.06 (m, 6H, Harom), 7.53 (d, 1H, J(α,β) = 15.5 Hz, H-α), 7.39 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.24 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 6.20 (s, 2H, CH2Ph); 13C-NMR (75 MHz): 171.23 (c-2), 154.98 (C-5´), 151.16 (C-2´), 149.11 (C-3´´), 141.49 (C-3a), 134.11 (C-β), 130.91 (C-6´´), 130.22 (C-4´´), 129.68 (C-1´´), 128.40 (C-6), 128.01 (C-7a), 124.70 (C-7), 123.33 (C-5´´), 123.65 (C-3´), 116.78 (C-4´), 111.00 (C-α), 51.38 (CH2Ph), 128.77, 128.70, 119.12.
3-Benzyl-2-((E)-2-{5-[3-(trifluoromethyl)phenyl]furan-2-yl}vinyl)-1,3-benzothiazolium bromide (7f). Reaction time: 90 min; yield: 66%; m.p. 250-254°C; Calc. for C27H19BrF3NOS (542.41): 59.79% C, 3.53% H, 14.73% Br, 2.58% N, 5.91% S; found: 60.10% C, 3.43% H, 14.86% Br, 2.64% N, 6.05% S; UV: 463 (3.58); 1H-NMR (300 MHz): 8.49 (d, 1H, J(4,5) = 8.1 Hz, H-4), 8.31 (d, 1H, J(6,7) = 8.3 Hz, H-7), 8.21-8.29 (m, 5H, Harom), 8.19 (d, 1H, J(α,β) = 15.7 Hz, H-β), 7.98 – 8.06 (m, 6H, Harom), 7.79 (d, 1H, J(α,β) = 15.7 Hz, H-α), 7.53 (d, 1H, J(3´,4´) = 3.6 Hz, H-3´), 7.39 (d, 1H, J(3´,4´) = 3.6 Hz, H-4´), 6.20 (s, 2H, CH2Ph); 13C-NMR (75 MHz): 171.65 (C-2), 153.18 (C-5´), 150.29 (C-2´), 141.33 (C-3a), 133.91 (C-β), 130.83 (C-5´), 130.50 (C-4´´), 130.03 (C-6´´), 129.61 (C-6), 129.12 (C-2´´), 128.49 (C-3´´), 128.40 (C-7a), 128.16 (C-5), 128.81 (C-7), 124.58 (C-3´), 123.23 (C-1´), 116.83 (C-4), 115.36 (C-4´), 110.72 (C-α), 51.4 (CH2Ph), 134.28, 127.98, 126.92.
3-Benzyl-2-{(E)-2-[5-(2-bromophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium bromide (7g). Reaction time: 120 min; yield: 52%; m.p. 220-224°C; Calc. for C26H18Br2NOS (553.31): 56.44% C, 3.46% H, 28.88% Br, 2.53% N, 5.80% S; found: 56.65% C, 3.33% H, 29.07% Br, 2.84% N, 6.43% S; 1H-NMR (300 MHz): 8.48 (d, 1H, J(4,5) = 8.2 Hz, H-4), 8.28 (d, 1H, J(6,7) = 8.1 Hz, H-7), 8.10-8.26 (m, 5H, Harom), 8.08 (d, 1H, J(α,β) = 15.5 Hz, H-β), 7.79 – 7.84 (m, 6H, Harom), 7.62 (d, 1H, J(α,β) = 15.5 Hz, H-α), 7.59 (d, 1H, J(3´,4´) = 3.6 Hz, H-3´), 7.53 (d, 1H, J(3´,4´) = 3.6 Hz, H-4´), 6.27 (s, 2H, CH2Ph); 13C-NMR (75 MHz): 171.68 (C-2), 155.12 (C-5´), 150.21 (C-2´), 141.36 (C-3a), 133.89 (C-β), 130.95 (C-5´), 129.82 (C-4´´), 129.60 (C-6´´), 129.01 (C-6), 128.79 (C-2´´), 128.46 (C-3´´), 128.38 (C-7a), 128.19 (C-5), 128.11 (C-7), 124.55 (C-3´), 123.11 (C-1´), 116.76 (C-4), 114.67 (C-4´), 110.24 (C-α), 51.33 (CH2Ph), 134.46, 134.23, 126.85.
3-Benzyl-2-{(E)-2-[5-(2,4-dichlorophenyl)furan-2-yl]vinyl}-1,3-benzothiazolium bromide (7h). Reaction time: 120 min; yield: 43%; m.p. 227-230°C; Calc. for C26H18BrCl2NOS (543.30): 57.48% C, 3.34% H, 13.05% Br, 14.71% Cl, 2.58% N, 5.90% S; found: 57.62% C, 3.23% H, 13.15% Br, % 14.81 Cl, 2.64% N, 5.85% S; UV: 463 (3.59); 1H-NMR (300 MHz): 8.48 (d, 1H, J(4,5) = 8.1 Hz, H-4), 8.28 (d, 1H, J(6,7) = 8.1 Hz, H-7), 8.10 – 8.26 (m, 5H, Harom), 8.08 (d, 1H, J(α,β) = 15.4 Hz, H-β), 7.78 – 8.07 (m, 6H, Harom), 7.62 (d, 1H, J(α,β) = 15.4 Hz, H-α), 7.59 (d, 1H, J(3´,4´) = 3.7 Hz, H-3´), 7.52 (d, 1H, J(3´,4´) = 3.7 Hz, H-4´), 6.27 (s, 2H, CH2Ph). δC (75 MHz): 171.65 (C-2), 153.18 (C-5´), 150.29 (C-2´), 141.33 (C-3a), 133.91(C-β), 130.83 (C-5´), 130.03 (C-4´´), 129.61 (C-6´´), 129.12 (C-6), 128.49 (C-2´´), 128.40 (C-3´´), 128.16 (C-7a), 127.98 (C-5), 126.91 (C-7), 124.56 (C-3´), 123.23 (C-1´), 116.83 (C-4), 11.36 (C-4´), 110.71 (C-α), 51.40 (CH2Ph), 134.27, 130.49, 125.81.
2-{(E)-2-[5-(Methoxycarbonyl)-4H-furo[3,2-b]pyrrol-2-yl]vinyl}-3-methyl-1,3-benzothiazolium iodide (8a). Yield 61%; m.p. 288-292°C (methanol); Calc. for C18H15IN2O3S (466.29): 46.36% C, 3.24% H, 6.01% N, 6.88% S; found: 46.51% C, 3.33% H, 6.03% N, 6.92% S. UV: 483 (3.66); 1H-NMR (500 MHz): 12.24 (s, 1H, NH), 8.42 (d, 1H, H-7), 8.25 (d, 1H, H-4), 8.11 (d, 1H, J(α,β) = 15.4 Hz, H-β), 7.88 (t, 1H, H-5), 7.79 (t, 1H, H-6), 7.63 (d, 1H, J(α,β) = 15.4 Hz, H-α), 7.48 (s, 1H, H-3´), 6.89 (s, 1H, H-6´), 4.32 (s, 3H, N+CH3), 3.87 (s, 3H, CO2CH3); 13C-NMR (125 MHz): 170.59 (C-2), 161.27 (CO2CH3), 156.07 (C-2´), 151.54 (C-6´a), 142.26 (C-3a), 134.37 (C-β), 130.79 (C-3´a), 129.2 (C-5´), 128.49 (C-6), 127.82 (C-7a), 124.1 (C-7), 121.63 (C-5), 116.86 (C-4), 109.91 (C-α), 108.8 (C-3´), 95.65 (C-6´), 52.18 (CO2CH3), 36.30 (N+CH3).
3-Benzyl-2-{(E)-2-[5-(methoxycarbonyl)-4H-furo[3,2-b]pyrrol-2-yl]vinyl}-1,3-benzothiazolium bromide (8b). Reaction time: 120 min; yield: 70%; m.p. 235-238°C; Calc. for C24H19BrN2O3S (495.39): 58.19% C, 3.87% H, 5.65% N, 6.47% S; found: 58.40% C, 3.72% H, 5.72% N, 6.54% S; UV: 497 (3.76); 1H-NMR (500 MHz): 12.30 (s, 1H, NH), 8.51 (d, 1H, J(4,5) = 8.2 Hz, H-4), 8.27 (d, 1H, J(α,β) = 15.3 Hz, H-β), 8.20 (d, 1H, J(6,7) = 8.1 Hz, H-4), 7.84 (t, 1H, H-6), 7.79 (t, 1H, H-5), 7.76 (d, 1H, J(α,β) = 15.3 Hz, H-α), 7.60 (s, 1H, H-3´), 7.44-7.36 (m, 5H, Harom), 6.86 (s, 1H, H-5´), 6.29 (s, 2H, N+CH2), 3.87 (s, 3H, CO2CH3); 13C-NMR (125 MHz): 171.35 (C-2), 160.99 (C-4´), 155.92 (C-2´), 151.69 (C-6a´), 141.41 (C-3a), 135.43 (C-β), 134.52 (C-3a´), 129.63 (C-6), 129.54 (CO2CH3), 128.32 (C-5), 127.98 (C-7a), 124.67 (C-4), 116.75 (C-7), 109.38 (C-3´), 109.02 (C-α), 95.55 (C-5´), 51.98 (CO2CH3), 51.13 (N+CH2), 133.98, 129.21, 128.47, 126.73.
3-Benzyl-2-{(E)-2-[5-(ethoxycarbonyl)-4-methylfuro[3,2-b]pyrrol-2-yl]vinyl}-1,3-benzothiazolium bromide (8c). Reaction time: 110 min; yield: 48%; m.p. 223-226°C; Calc. for C26H23BrN2O3S (523.44): 59.66% C, 4.43% H, 5.35% N, 6.13% S; found: 59.84% C, 4.20% H, 5.27% N, 6.07% S; UV: 497 (3.83); 1H-NMR (500 MHz): 8.51 (d, 1H, J(4,5) = 8.3 Hz, H-4), 8.29 (d, 1H, J(α,β) = 15.3 Hz, H-β), 8.21 (d, 1H, J(6,7) = 8.2 Hz, H-7), 7.84 (t, 1H, H-6), 7.79 (t, 1H, H-5), 7.76 (d, 1H, J(α,β) = 15.3 Hz, H-α), 7.69 (s, 1H, H-3´), 7.45-7.36 (m, 5H, Harom), 6.83 (H-6´), 6.29 (s, 2H, N+CH2), 4.31 (q, 2H, CO2CH2CH3), 4.01 (NCH3), 1.34 (t, 3H, CO2CH2CH3); 13C-NMR (125 MHz): 171.36 (C-2), 160.56 (CO2CH2CH3), 155.55 (C-2´), 149.13 (C-6a´), 141.38 (C-3a), 135.59 (C-β), 129.66 (C-6), 129.30 (C-4´), 133.94, 129.26, 128.50, 128.37 (C-5), 128.05 (C-7a), 124.60 (C-4), 116.72 (C-7), 109.36 (C-α), 108.86 (C-3´), 96.84 (C-5´), 60.59 (CO2CH2CH3), 51.17 (N+CH2), 35.08 (NCH3), 14.30 (CO2CH2CH3), 133.94, 129.26, 128.50, 126.77.
3-Benzyl-2-{(E)-2-[5-(ethoxycarbonyl)-4-benzylfuro[3,2-b]pyrrol-2-yl]vinyl}-1,3-benzothiazolium bromide (8d). Reaction time: 120 min; yield: 67%; m.p. 242-245°C; Calc. for C32H27BrN2O3S (599.54): 64.11% C, 4.54% H, 4.67% N, 5.35% S; found: 64.28% C, 4.38% H, 4.72% N, 5.41% S; UV: 497 (3.98); 1H-NMR (500 MHz): 8.49 (d, 1H, J(4,5) = 8.1 Hz, H-4), 8.27 (d, 1H, J(α,β) = 15.3 Hz, H-β), 8.21 (d, 1H, J(6,7) = 8.1 Hz, H-7), 7.85 (t, 1H, H-6), 7.79 (t, 1H, H-5), 7.76 (d, 1H, J(α,β) = 15.3 Hz, H-α), 7.52 (s, 1H, H-3´), 7.44-7.25 (m, 10H, Harom), 6.99 (s, 1H, H-5´), 6.28 (N+CH2), 5.78 (NCH2), 4.31 (q, 2H, CO2CH2CH3), 1.32 (t, 3H, CO2CH2CH3); 13C-NMR (125 MHz): 171.51 (C-2), 160.59 (CO2CH2CH3), 155.75 (C-2´), 149.46 (C-6a´), 141.44 (C-3a), 135.40 (C-β), 134.50 (C-3a´), 129.74 (C-6), 129.30 (C-4´), 128.42 (C-5), 116.81 (C-4), 109.82 (C-α), 108.98 (C-3´), 98.01(C-5´), 60.73 (CO2CH2CH3), 51.26 (N+CH2), 50.17 (NCH2), 14.25 (CO2CH2CH3), 137.68, 133.94, 129.25, 128.80, 128.54, 127.78, 127.10.
3-Benzyl-2-{(E)-2-[5-(methoxycarbonyl)-6-methoxymethylfuro[2,3-b]pyrrol-2-yl]vinyl}-1,3-benzo-thiazolium bromide (9). Reaction time: 160 min; yield: 45%; m.p. 278-282°C; Calc. for C26H23BrN2O4S (539.44): 57.89% C, 4.30% H, 5.19% N, 5.94% S; found: 58.12% C, 4.18% H, 5.27% N, 5.95% S; 1H-NMR (500 MHz): 8.48 (d, 1H, J(4,5) = 8.3 Hz, H-4), 8.30 (d, 1H, J(α,β) = 15.3 Hz, H-β), 8.22 (d, 1H, J(6,7) = 8.1 Hz, H-7), 7.87 (t, 1H, H-6), 7.81 (t, 1H, H-6), 7.68 (d, 1H, J(α,β) = 15.3 Hz, H-α), 7.67 (s, 1H, H-4´), 7.42-7.37 (m, 5H, Harom), 7.19 (s, 1H, H-3´), 6.26 (N+CH2), 5.83 (s, 2H, CH2OCH3), 3.87 (s, 3H, CO2CH3), 3.31 (s, 3H, CH2OCH3).

Acknowledgements

A. K. thanks the VEGA Grant Agency of Slovak Ministry of Education for financial support of project No. 1/0069/03. The authors are grateful to Dr. Darina Tóthová for UV spectra measurement. Z. P. appreciates Prof. Dr. Ferenc Fülöp’s kindness and help during her CEEPUS SK-20 stay at the Institute of Pharmaceutical Chemistry, University of Szeged, Hungary.

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