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A novel approach to incorporate fused heteroaromatic chromophores into polythiophenes
Synthetic Metals 107 Ž1999. 93–96 www.elsevier.comrlocatersynmet
A novel approach to incorporate fused heteroaromatic chromophores into polythiophenes Saeid J. Behroozi, Braja K. Mandal
)
Department of Biological, Chemical and Physical Sciences, Illinois Institute of Technology, 3255 South Dearborn, Chicago, IL 60616, USA Received 22 June 1999; accepted 16 July 1999
Abstract A novel polythiophene, containing pendant fused heteroaromatic chromophores, has been synthesized by electrochemical polymerization of a new thiophene monomer, 3-Ž2-indolizinothiophene.. The structural characterization and electrochemical properties of the monomer are described. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Polythiophenes; Indolizines; Cyclazines; Electrochemical polymerization
1. Introduction Polythiophenes have attracted significant attention recently due to their intrinsically low band gaps, ease of the electrochemical preparation of films, and relatively good environmental stabilities w1–3x. Many theoretical and experimental efforts have been devoted to the design and preparation of structurally diverse low band gap polythiophenes by the derivatization of thiophene, primarily at the 3-position, with a wide variety of aryl substituents w4–13x. However, studies on attaching fused electron rich-heteroaromatic systems, such as substituted aryl amines, have been limited. Aryl amines have been studied extensively for their electronic conduction Žthrough the hole migration mechanism. and fluorescencent characteristics in the area of light-emitting diodes w14–16x. For various reasons, we and other groups have investigated compounds containing the indolizine moiety. First, the fully or partially reduced indolizine analogues mimic biologically active alkaloids w17–20x. Second, the indolizine derivatives exhibit fluorescent characteristics and have been considered as potential hole transport agents for electroluminescent devices w14–16x. Our group is inter-
)
Corresponding author. Department of Biological, Chemical and Physical Sciences, Illinois Institute of Technology, Room 182, 3101 S. Dearborn Street, Chicago, IL 60616-3793, USA. Tel.: q1-3125673446; fax: q1-3125673436; e-mail: [email protected]
ested in the synthesis and electrochemical behavior of heteroaryl substituted polythiophenes. Towards this end, we have recently reported a new polythiophene containing pendant carbazole Žphotoconducting chromophore. units w21x. Aryl substitution at the 3-position of thiophene is straightforward and is preferentially accomplished by coupling reactions. These include a Suzuki-type cross-coupling reaction of thiophene boronic acid and a haloaryl compound in the presence of palladium catalyst w1–3x and a reaction between halothiophene and aryl magnesium halide in the presence of an NiŽII. catalyst w22,23x. In this article, we describe a new approach to incorporate fused heteroaromatic systems, such as indolizine, at the 3-position of the thiophene ring. 2. Results and discussion The new polythiophene containing pendant indolizine chromophores was synthesized as shown in Scheme 1. The new compound 1 was prepared in 73% yield by monobromination of commercially available 3-acetylthiophene in the presence of copperŽII. bromide w24x. The Chichibabin reaction w25,26x of 1 with 2-picoline provided the bromide salt 2 in near quantitative yield. On treatment with aqueous sodium bicarbonate, 2 readily underwent intramolecular condensation to give 3-Ž2-indolizinothiophene. 3 in 83% yield. Potentiostatic polymerization of monomer 3 was performed in a single compartment, three electrode assembly
0379-6779r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 Ž 9 9 . 0 0 1 5 2 - 6
94
S.J. Behroozi, B.K. Mandalr Synthetic Metals 107 (1999) 93–96
Scheme 1. Syntheses of new thiopene derivatives.
using glassy carbon as the working electrode, a platinum wire as the counter electrode, and AgrAgq as the reference electrode. Acetonitrile was used as solvent, where the concentrations of the electrolyte Žtetrabutylammonium tetrafluoroborate. and the monomer were 0.1 and 0.01 M, respectively. The cyclic voltammogram of the monomer is shown in Fig. 1a. The increase in current and reduction potential on each scan corresponds to the formation of polythiophene derivative PTIn on the electrode surface ŽFig. 1b.. Similar results were obtained with other solvents such as methylene chloride. We also performed the cyclic voltammetry of the PTIn films Žobtained after 25 cycles, followed by washing with dry acetonitrile. in a fresh electrolyte solution containing no monomer 3. The p-doping process is reversible and varies linearly with the scan rate ŽFig. 2.. It is noteworthy that the films obtained in this manner cannot be reversibly n-doped w21x. The PTIn was insoluble in common organic solvents, thus preventing further characterization of the polymer. We have also prepared another new thiophene monomer substituted with the cyclazine chromophore Ž4. from monomer 3 by cycloaddition of dimethyl acetylenedicarboxylate ŽDMAD. in the presence of palladium on activated carbon catalyst ŽScheme 1.. Surprisingly, the 4 did not polymerize under the conditions used for 3. This
behavior is somewhat unusual, since in a similar study, we were able to polymerize thiophene monomers containing bulky groups such as pyrene w27x and carbazole w21x. This lack of reactivity might be due to the presence of two electron withdrawing carbomethoxy groups. All new compounds have been thoroughly characterized and are in good agreement with the proposed structures in Scheme 1. The electronic absorption spectra of compounds 1, 3 and 4 are shown in Fig. 3. The absorption due to the 3-substituted thiophene ring in all the compounds showed a strong peak near 260 nm. The indolizine moiety showed a weak peak at 348 nm, while the cyclazine residue exhibited two strong peaks at 342 and 416 nm. In conclusion, we have demonstrated a new approach for the preparation of two new 3-substituted heteroaryl thiophene monomers. The thiophene monomer containing the indolizine moiety forms polymeric thin films on electrode surfaces. Further studies involving the incorporation of a long aliphatic chain through the indolizine ring is now underway Že.g., solution properties. on these polymers and will be published separately. 3. Experimental section All starting materials, reagents, and tetrahydrofuran ŽTHF. were purchased from Aldrich Chemical and were of
S.J. Behroozi, B.K. Mandalr Synthetic Metals 107 (1999) 93–96
95
Fig. 3. Electronic absorption spectra of 1, 3 and 4 in dichloromethane.
pieces of sodium metal while distilled into a trap and was checked for dryness with benzophenone prior to use. The trace of water in toluene was removed using a Dean–Stark apparatus. Dichloromethane and acetonitrile used for the polymerization were distilled over calcium hydride and stored over molecular sieves.
Fig. 1. Petentiostatic polymerization of monomer 3 Ž0.01 M. in acetonitrile containing 0.1 M NBu 4 BF4 at 100 mVrs Žvs. AgrAgq .. Ža. First cycle, Žb. second and consequent cycles. The increase in current Žwith increasing number of cycles. is due to the formation of an electroactive polymer layer on the surface of the working electrode.
the highest purity available. The rest of the solvents were purchased from Fisher Scientific. THF was dried over
3.1. 3-Bromoacetylthiophene (1) In a 50-ml three-necked round bottom flask, 3acetylthiophene Ž0.13 g, 1 mmol. and copperŽII. bromide Ž0.45 g, 2 mmol. were suspended in 20 ml of dry THF under an argon atmosphere. The mixture was brought to reflux and kept at this temperature until all of the starting materials were consumed Žca. 6–8 h. The solution was filtered hot and the filtrate was evaporated in a rotovap to afford a light yellow viscous oil. The product was obtained as white needles after column chromatography Žsilica, 1:1 hexanerdichloromethane.. Yield: 0.15 g Ž73%., mp 618C. FTIR: n , 3094.2, 2952.5, 1680.8, 1505.2, 1400.9, 1283.6, 1224.6, 1183.5, 1063.3, 902.0, 882.3, 802.9, 708.4, 660.2, 620.7 cmy1 . 1 H NMR Ž300 MHz CDCl 3 .: d 8.3 Žs, 1H., 7.7 Žd, 1H., 7.5 Žd, 1H., 4.5 Žs, 2H.. 13 C NMR Ž75 MHz CDCl 3 .: d 185.5, 138.7, 133.7, 127.2, 126.8, 31.5. MS: major fragments 205, 186, 124, 111, 95, 78, 67, 61, 54, 48, 40. Anal. Calcd. for C 6 H 5 BrOS: C, 35.14; H, 2.46. Found: C, 35.27; H, 2.47. 3.2. 3-(2-Indolizinothiophene) (3)
Fig. 2. Cyclic voltammograms of PTIn film on glassy carbon electrode, in acetonitrile containing 0.1 M NBu 4 BF4 , taken at increasing scan rates Žvs. AgrAgq ..
To a suspension of the 3-bromoacetylthiophene Ž1.03 g, 5 mmol. in diethyl ether Ž35 ml. was added 2-picoline Ž2.33 g, 25 mmol. and stirred at r.t. for 8 h to obtain the bromide salt 2. The salt was filtered, washed with diethyl ether to remove excess 2-picoline, and dried in an oven at
96
S.J. Behroozi, B.K. Mandalr Synthetic Metals 107 (1999) 93–96
608C for 2 h to afford 1.43 g of the salt which was then subjected to the cyclization reaction without further purification. The cyclization was performed by refluxing a mixture of the salt and sodium bicarbonate Ž1.43 g. in a 250-ml flask containing 40 ml of water for about 2.5 h until the mixture was transformed into a white cake. The solid was filtered, washed with water to remove excess sodium bicarbonate and other water soluble impurities, and dried in vacuo at 608C for 2 h. The title compound was obtained in high purity. Yield: 0.8 g Ž83%., mp 228–2308C. 1 H NMR Ž300 MHz CDCl 3 .: d 7.9 Žd, 1H., 7.5 Žs, 1H., 7.4–7.2 Žm, 4H., 6.8–6.6 Žm, 2H., 6.4 Žt, 1H.. 13 C NMR Ž75 MHz CDCl 3 .: d 136.5, 128.3, 126.5, 125.8, 125.0, 124.8, 118.9, 118.7, 117.4, 110.4, 109.3, 96.9. MS: 199.2698; major fragments 165, 149, 120, 84, 65. Anal. Calcd. for C 12 H 9 NS: C, 72.33; H, 4.55; N, 7.03. Found: C, 72.38; H, 4.53; N, 6.99.
Acknowledgements This work is supported in part by the US Army Research Office under grant aDAAH04-96-I-0130 and by the IIT-ERIF grant. We thank Christopher J. Walsh and Thanasat Sooksimuang for their help in electrochemical studies. References w1x w2x w3x w4x w5x w6x w7x w8x w9x
3.3. 3-(3-(1,2-Dicarbomethoxycycl[3.2.2]azino)thiophene) (4) To a solution of TPIn Ž0.2 g, 1.0 mmol. in dry toluene Ž30 ml. under an argon atmosphere was added 5% palladium on activated carbon Ž0.14 eq.. Dimethylacetylene dicarboxylate Ž270.45 ml, 2.2 mmol. was added dropwise to the solution which was brought to reflux for 6 h, at which time all of the indolizine starting material was consumed, as indicated by thin layer chromatography. The solution was filtered under vacuum while hot to remove palladium catalyst. The filtrate was concentrated under reduced pressure and the dark residue purified by column chromatography Žsilica, CH 2 Cl 2 . to afford a fluorescent yellow product. Yield: 0.23 g Ž67%., mp 152–1538C. FTIR: n 3108.8, 2950.2, 1732.3, 1704.4, 1487.3, 1446.4, 1275.0, 1220.5, 1116.2, 1070.7, 791.6 cmy1 . 1 H NMR Ž300 MHz CDCl 3 .: d 8.4 Žd, 1H., 8.0–7.9 Žm, 2H., 7.8–7.7 Žm, 1H., 7.5 Žm, 1H., 7.4 Žs, 2H.. 4.1 Žs, 3H., 4.0 Žs, 3H.. 13 C NMR ŽMHz CDCl 3 .: d 167.2, 164.3, 134.8, 132.1, 131.3, 128.7, 127.5, 126.5, 125.5, 124.2, 124.1, 122.2, 116.0, 113.9, 111.5, 111.3, 53.1, 51.8. MS: 339.3650; major fragments 304, 271, 242, 214, 172, 101, 64, 46. Anal. Calcd. for C 18 H 13 NO4 S: C, 63.71; H, 3.86; N, 4.13. Found: C, 63.81; H, 3.89; N, 4.09.
w10x w11x w12x w13x w14x w15x w16x w17x w18x w19x w20x w21x w22x w23x w24x w25x w26x w27x
R.D. McCullough, Adv. Mater. 10 Ž1998. 93. J. Roncali, Chem. Rev. 97 Ž1997. 173. J. Roncali, Chem. Rev. 92 Ž1992. 711. J.M. Toussaint, J.L. Bredas, Macromolecules 26 Ž1993. 5240. Y.-S. Lee, M. Kertesz, J. Chem. Phys. 88 Ž1988. 2609. J.L. Bredas, Synth. Met. 17 Ž1987. 115. M. Kertesz, Y.-S. Lee, J. Phys. Chem. 91 Ž1987. 2690. H. Sarker, Y. Gofer, J.G. Killian, T.O. Poehler, P.C. Searson, Synth. Met. 88 Ž1997. 179. M. Onoda, H. Nakayama, S. Morita, K. Yoshino, Synth. Met. 55r57 Ž1993. 275. A. Rudge, I. Raistrick, S. Gottesfeld, J.P. Ferraris, Elctrochim. Acta 39 Ž1993. 273. M. Ueda, Y. Miyaji, T. Ito, Y. Oba, T. Sone, Macromolecules 24 Ž1991. 2694. M. Sato, S. Tanaka, K. Kaeriyama, Makromol. 190 Ž1989. 1233. M. Sato, S. Tanaka, K. Kaeriyama, J. Chem. Soc. Chem. Commun. Ž1987. 1725. D.B. Romero, F. Nuesch, T. Benaaai, D. Ades, A. Siove, L. Zuppirol, Adv. Mater. 9 Ž1997. 1158. H.K. Shim, H.J. Kim, T. Ahn, I.N. Kang, T.Y. Zyung, Synth. Met. 91 Ž1997. 289. E.S. Kolb, R.A. Gaudiana, P.G. Mehta, Macromolecules 29 Ž1996. 2359. J.O. Smith, B.K. Mandal, Heterocycl. Chem. 34 Ž1997. 1441. J.O. Smith, PhD Thesis, Illinois Institute of Technology, 1996. R.P. Polniaszek, S.E. Belmont, J. Org. Chem. 55 Ž1990. 4688. J.W. Daly, T.F. Spande, in: S.W. Pelletier ŽEd.., Alkaloids: Chemical and Biological Perspectives, Chap. 1, Wiley, New York, 1986. C.J. Walsh, T. Sooksimuang, B.K. Mandal, Macromolecules 32 Ž1999. 2397. V. Bethmont, A.E. Kassmi, F. Fache, M. Lemaire, Synth. Met. 93 Ž1998. 197. K. Tamao, S. Kodama, I. Nakajima, M. Kumada, A. Minato, K. Suzuki, Tetrahedron 38 Ž1982. 3347. L.C. King, K.G. Ostrum, J. Org. Chem. 29 Ž1964. 3459. R.J. Windgassen, W.H. Saunders Jr., V. Boekelheide, J. Am. Chem. Soc. 81 Ž1959. 1459. A.E. Chichibabin, Ber. 60 Ž1927. 1607. S.J. Behroozi, B.K. Mandal, unpublished data.
A novel approach to incorporate fused heteroaromatic chromophores into polythiophenes Saeid J. Behroozi, Braja K. Mandal
)
Department of Biological, Chemical and Physical Sciences, Illinois Institute of Technology, 3255 South Dearborn, Chicago, IL 60616, USA Received 22 June 1999; accepted 16 July 1999
Abstract A novel polythiophene, containing pendant fused heteroaromatic chromophores, has been synthesized by electrochemical polymerization of a new thiophene monomer, 3-Ž2-indolizinothiophene.. The structural characterization and electrochemical properties of the monomer are described. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Polythiophenes; Indolizines; Cyclazines; Electrochemical polymerization
1. Introduction Polythiophenes have attracted significant attention recently due to their intrinsically low band gaps, ease of the electrochemical preparation of films, and relatively good environmental stabilities w1–3x. Many theoretical and experimental efforts have been devoted to the design and preparation of structurally diverse low band gap polythiophenes by the derivatization of thiophene, primarily at the 3-position, with a wide variety of aryl substituents w4–13x. However, studies on attaching fused electron rich-heteroaromatic systems, such as substituted aryl amines, have been limited. Aryl amines have been studied extensively for their electronic conduction Žthrough the hole migration mechanism. and fluorescencent characteristics in the area of light-emitting diodes w14–16x. For various reasons, we and other groups have investigated compounds containing the indolizine moiety. First, the fully or partially reduced indolizine analogues mimic biologically active alkaloids w17–20x. Second, the indolizine derivatives exhibit fluorescent characteristics and have been considered as potential hole transport agents for electroluminescent devices w14–16x. Our group is inter-
)
Corresponding author. Department of Biological, Chemical and Physical Sciences, Illinois Institute of Technology, Room 182, 3101 S. Dearborn Street, Chicago, IL 60616-3793, USA. Tel.: q1-3125673446; fax: q1-3125673436; e-mail: [email protected]
ested in the synthesis and electrochemical behavior of heteroaryl substituted polythiophenes. Towards this end, we have recently reported a new polythiophene containing pendant carbazole Žphotoconducting chromophore. units w21x. Aryl substitution at the 3-position of thiophene is straightforward and is preferentially accomplished by coupling reactions. These include a Suzuki-type cross-coupling reaction of thiophene boronic acid and a haloaryl compound in the presence of palladium catalyst w1–3x and a reaction between halothiophene and aryl magnesium halide in the presence of an NiŽII. catalyst w22,23x. In this article, we describe a new approach to incorporate fused heteroaromatic systems, such as indolizine, at the 3-position of the thiophene ring. 2. Results and discussion The new polythiophene containing pendant indolizine chromophores was synthesized as shown in Scheme 1. The new compound 1 was prepared in 73% yield by monobromination of commercially available 3-acetylthiophene in the presence of copperŽII. bromide w24x. The Chichibabin reaction w25,26x of 1 with 2-picoline provided the bromide salt 2 in near quantitative yield. On treatment with aqueous sodium bicarbonate, 2 readily underwent intramolecular condensation to give 3-Ž2-indolizinothiophene. 3 in 83% yield. Potentiostatic polymerization of monomer 3 was performed in a single compartment, three electrode assembly
0379-6779r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 Ž 9 9 . 0 0 1 5 2 - 6
94
S.J. Behroozi, B.K. Mandalr Synthetic Metals 107 (1999) 93–96
Scheme 1. Syntheses of new thiopene derivatives.
using glassy carbon as the working electrode, a platinum wire as the counter electrode, and AgrAgq as the reference electrode. Acetonitrile was used as solvent, where the concentrations of the electrolyte Žtetrabutylammonium tetrafluoroborate. and the monomer were 0.1 and 0.01 M, respectively. The cyclic voltammogram of the monomer is shown in Fig. 1a. The increase in current and reduction potential on each scan corresponds to the formation of polythiophene derivative PTIn on the electrode surface ŽFig. 1b.. Similar results were obtained with other solvents such as methylene chloride. We also performed the cyclic voltammetry of the PTIn films Žobtained after 25 cycles, followed by washing with dry acetonitrile. in a fresh electrolyte solution containing no monomer 3. The p-doping process is reversible and varies linearly with the scan rate ŽFig. 2.. It is noteworthy that the films obtained in this manner cannot be reversibly n-doped w21x. The PTIn was insoluble in common organic solvents, thus preventing further characterization of the polymer. We have also prepared another new thiophene monomer substituted with the cyclazine chromophore Ž4. from monomer 3 by cycloaddition of dimethyl acetylenedicarboxylate ŽDMAD. in the presence of palladium on activated carbon catalyst ŽScheme 1.. Surprisingly, the 4 did not polymerize under the conditions used for 3. This
behavior is somewhat unusual, since in a similar study, we were able to polymerize thiophene monomers containing bulky groups such as pyrene w27x and carbazole w21x. This lack of reactivity might be due to the presence of two electron withdrawing carbomethoxy groups. All new compounds have been thoroughly characterized and are in good agreement with the proposed structures in Scheme 1. The electronic absorption spectra of compounds 1, 3 and 4 are shown in Fig. 3. The absorption due to the 3-substituted thiophene ring in all the compounds showed a strong peak near 260 nm. The indolizine moiety showed a weak peak at 348 nm, while the cyclazine residue exhibited two strong peaks at 342 and 416 nm. In conclusion, we have demonstrated a new approach for the preparation of two new 3-substituted heteroaryl thiophene monomers. The thiophene monomer containing the indolizine moiety forms polymeric thin films on electrode surfaces. Further studies involving the incorporation of a long aliphatic chain through the indolizine ring is now underway Že.g., solution properties. on these polymers and will be published separately. 3. Experimental section All starting materials, reagents, and tetrahydrofuran ŽTHF. were purchased from Aldrich Chemical and were of
S.J. Behroozi, B.K. Mandalr Synthetic Metals 107 (1999) 93–96
95
Fig. 3. Electronic absorption spectra of 1, 3 and 4 in dichloromethane.
pieces of sodium metal while distilled into a trap and was checked for dryness with benzophenone prior to use. The trace of water in toluene was removed using a Dean–Stark apparatus. Dichloromethane and acetonitrile used for the polymerization were distilled over calcium hydride and stored over molecular sieves.
Fig. 1. Petentiostatic polymerization of monomer 3 Ž0.01 M. in acetonitrile containing 0.1 M NBu 4 BF4 at 100 mVrs Žvs. AgrAgq .. Ža. First cycle, Žb. second and consequent cycles. The increase in current Žwith increasing number of cycles. is due to the formation of an electroactive polymer layer on the surface of the working electrode.
the highest purity available. The rest of the solvents were purchased from Fisher Scientific. THF was dried over
3.1. 3-Bromoacetylthiophene (1) In a 50-ml three-necked round bottom flask, 3acetylthiophene Ž0.13 g, 1 mmol. and copperŽII. bromide Ž0.45 g, 2 mmol. were suspended in 20 ml of dry THF under an argon atmosphere. The mixture was brought to reflux and kept at this temperature until all of the starting materials were consumed Žca. 6–8 h. The solution was filtered hot and the filtrate was evaporated in a rotovap to afford a light yellow viscous oil. The product was obtained as white needles after column chromatography Žsilica, 1:1 hexanerdichloromethane.. Yield: 0.15 g Ž73%., mp 618C. FTIR: n , 3094.2, 2952.5, 1680.8, 1505.2, 1400.9, 1283.6, 1224.6, 1183.5, 1063.3, 902.0, 882.3, 802.9, 708.4, 660.2, 620.7 cmy1 . 1 H NMR Ž300 MHz CDCl 3 .: d 8.3 Žs, 1H., 7.7 Žd, 1H., 7.5 Žd, 1H., 4.5 Žs, 2H.. 13 C NMR Ž75 MHz CDCl 3 .: d 185.5, 138.7, 133.7, 127.2, 126.8, 31.5. MS: major fragments 205, 186, 124, 111, 95, 78, 67, 61, 54, 48, 40. Anal. Calcd. for C 6 H 5 BrOS: C, 35.14; H, 2.46. Found: C, 35.27; H, 2.47. 3.2. 3-(2-Indolizinothiophene) (3)
Fig. 2. Cyclic voltammograms of PTIn film on glassy carbon electrode, in acetonitrile containing 0.1 M NBu 4 BF4 , taken at increasing scan rates Žvs. AgrAgq ..
To a suspension of the 3-bromoacetylthiophene Ž1.03 g, 5 mmol. in diethyl ether Ž35 ml. was added 2-picoline Ž2.33 g, 25 mmol. and stirred at r.t. for 8 h to obtain the bromide salt 2. The salt was filtered, washed with diethyl ether to remove excess 2-picoline, and dried in an oven at
96
S.J. Behroozi, B.K. Mandalr Synthetic Metals 107 (1999) 93–96
608C for 2 h to afford 1.43 g of the salt which was then subjected to the cyclization reaction without further purification. The cyclization was performed by refluxing a mixture of the salt and sodium bicarbonate Ž1.43 g. in a 250-ml flask containing 40 ml of water for about 2.5 h until the mixture was transformed into a white cake. The solid was filtered, washed with water to remove excess sodium bicarbonate and other water soluble impurities, and dried in vacuo at 608C for 2 h. The title compound was obtained in high purity. Yield: 0.8 g Ž83%., mp 228–2308C. 1 H NMR Ž300 MHz CDCl 3 .: d 7.9 Žd, 1H., 7.5 Žs, 1H., 7.4–7.2 Žm, 4H., 6.8–6.6 Žm, 2H., 6.4 Žt, 1H.. 13 C NMR Ž75 MHz CDCl 3 .: d 136.5, 128.3, 126.5, 125.8, 125.0, 124.8, 118.9, 118.7, 117.4, 110.4, 109.3, 96.9. MS: 199.2698; major fragments 165, 149, 120, 84, 65. Anal. Calcd. for C 12 H 9 NS: C, 72.33; H, 4.55; N, 7.03. Found: C, 72.38; H, 4.53; N, 6.99.
Acknowledgements This work is supported in part by the US Army Research Office under grant aDAAH04-96-I-0130 and by the IIT-ERIF grant. We thank Christopher J. Walsh and Thanasat Sooksimuang for their help in electrochemical studies. References w1x w2x w3x w4x w5x w6x w7x w8x w9x
3.3. 3-(3-(1,2-Dicarbomethoxycycl[3.2.2]azino)thiophene) (4) To a solution of TPIn Ž0.2 g, 1.0 mmol. in dry toluene Ž30 ml. under an argon atmosphere was added 5% palladium on activated carbon Ž0.14 eq.. Dimethylacetylene dicarboxylate Ž270.45 ml, 2.2 mmol. was added dropwise to the solution which was brought to reflux for 6 h, at which time all of the indolizine starting material was consumed, as indicated by thin layer chromatography. The solution was filtered under vacuum while hot to remove palladium catalyst. The filtrate was concentrated under reduced pressure and the dark residue purified by column chromatography Žsilica, CH 2 Cl 2 . to afford a fluorescent yellow product. Yield: 0.23 g Ž67%., mp 152–1538C. FTIR: n 3108.8, 2950.2, 1732.3, 1704.4, 1487.3, 1446.4, 1275.0, 1220.5, 1116.2, 1070.7, 791.6 cmy1 . 1 H NMR Ž300 MHz CDCl 3 .: d 8.4 Žd, 1H., 8.0–7.9 Žm, 2H., 7.8–7.7 Žm, 1H., 7.5 Žm, 1H., 7.4 Žs, 2H.. 4.1 Žs, 3H., 4.0 Žs, 3H.. 13 C NMR ŽMHz CDCl 3 .: d 167.2, 164.3, 134.8, 132.1, 131.3, 128.7, 127.5, 126.5, 125.5, 124.2, 124.1, 122.2, 116.0, 113.9, 111.5, 111.3, 53.1, 51.8. MS: 339.3650; major fragments 304, 271, 242, 214, 172, 101, 64, 46. Anal. Calcd. for C 18 H 13 NO4 S: C, 63.71; H, 3.86; N, 4.13. Found: C, 63.81; H, 3.89; N, 4.09.
w10x w11x w12x w13x w14x w15x w16x w17x w18x w19x w20x w21x w22x w23x w24x w25x w26x w27x
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