- Email: [email protected]
One pot synthesis of bis-silicon-bridged stilbene derivatives
Available online at www.sciencedirect.com
Chinese Chemical Letters 18 (2007) 1436–1438 www.elsevier.com/locate/cclet
One pot synthesis of bis-silicon-bridged stilbene derivatives Chen Hui Li a, Hua Yu Qiu a, Cai Hong Xu b,* a
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Teachers College, Hangzhou 310012, China b Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China Received 24 July 2007
Abstract Bis-silicon-bridged stilbene derivatives were synthesized in a modified procedure that combined the preparation of bis[2(silyl)phenyl]acetylene and its intramolecular reductive cyclization in one pot. The results indicated that the one pot approach produced target products in a comparable yield to that of the two-step method reported previously. # 2007 Cai Hong Xu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Bis-silicon-bridged stilbene; Reductive cyclization; One pot synthesis
Ladder p-conjugated molecules have attracted considerable attention in the past decades, due to their fascinating properties relating to organic electronics and optoelectronics [1–3]. As a fundamental skeleton of new ladder pconjugated systems, we have focused our attention on silicon-bridge containing frameworks. Recently we have reported a facile and effective synthesis of bis-silicon-bridged stilbene homologues via a newly developed intramolecular reductive cyclization reaction [4–7]. The bis-silicon-bridged stilbene derivatives were synthesized via two-step reactions. The first one is preparation of bis[2-(silyl)phenyl]acetylenes from metalation and followed silylation of bis(2-bromophenyl)acetylene. Then the isolated bis[2-(silyl)phenyl]acetylenes further undergoes intramolecular reductive cyclization with lithium naphthalenide (LiNaph) as reductant and iodine as quenching agent to produce target molecules. In this work, we have combined the preparation of bis[2-(silyl)phenyl]acetylene and its intramolecular reductive cyclization in one pot procedure as shown in Scheme 1. This approach produced target products in a comparable yield to that of the two-step method reported previously. 1. Experimental 1
H and 13C nuclear magnetic resonance (NMR) spectra were recorded in CDCl3 solution with a Bruker WM 300 spectrometer. Elemental analysis for C and H were determined with Carlo Erba 1106 analyzer. Thin-layer chromatography (TLC) was performed on plates coated with 0.2 mm thick silica gel. Column chromatography was performed using silica gel as a stationary phase (200–300 mesh). All experiments were carried out under a nitrogen atmosphere. THF was distilled from sodium/benzophenone prior to use. All other chemicals were purchased from Aldrich or Acros and used as received. * Corresponding author. E-mail address: [email protected] (C.H. Xu). 1001-8417/$ – see front matter # 2007 Cai Hong Xu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2007.09.039
C.H. Li et al. / Chinese Chemical Letters 18 (2007) 1436–1438
1437
Scheme 1. .
1.1. Synthesis of bis-dimethylsilylene-bridged stilbene using HMe2SiCl for silylation To a solution of bis(2-bromophenyl)acetylene (0.43 g, 1.28 mmol) in THF (15 mL) was added hexane solution of n-BuLi (1.6 mol/L, 1.7 mL, 2.72 mmol) dropwise at 78 8C. After stirred for 1.5 h, HMe2SiCl (0.4 mL, 3.60 mmol) was added via syringe at the same temperature. The mixture was gradually warmed to room temperature with stirring over 7 h. Then the resulting mixture was added to the solution of lithium naphthalenide prepared from granular lithium (35.8 mg, 5.16 mmol) and naphthalene (661.4 mg, 5.16 mmol) in THF (4 mL). After stirred for 5 min, the reaction mixture was quenched with a THF (5 mL) solution of iodine (1.31 g, 5.16 mmol). A saturated Na2S2O3 aqueous solution was added, and the mixture was extracted with ether. The organic layer was washed with brine, dried over MgSO4, filtered, and concentrated under reduced pressure. The crude product was subjected to a silica gel column chromatography with hexane as an eluent (Rf = 0.29), and was purified by recrystalization from hexane to give 160.9 mg (0.55 mmol) of bis-silicon-bridged stilbene (R = H, R0 = Me) in 43% yield [4]. 1.2. Synthesis of bis-dimethylsilylene-bridged stilbene using Me2(NEt2)SiCl for silylation To a solution of bis(2-bromophenyl)acetylene (0.50 g, 1.49 mmol) in THF (15 mL) was added a hexane solution of n-BuLi (1.6 mol/L, 1.9 mL, 3.04 mmol) dropwise at 78 8C. After stirred for 1 h, Me2(NEt2)SiCl (0.51 g, 3.08 mmol) was added via syringe at the same temperature and the mixture was allowed to warm to room temperature over 8 h under stirring. Ethanol (0.2 mL, 3.42 mmol) and NH4Cl (18 mg, 0.34 mmol) were added to the resulting mixture under nitrogen stream, followed by stirring for 11 h. Then the resulting mixture was added to the solution of lithium naphthalenide prepared from granular lithium (41.4 mg, 5.97 mmol) and naphthalene (763.9 mg, 5.96 mmol) in THF (5 mL). After stirred for 5 min, the reaction mixture was quenched with a THF (5 mL) solution of iodine (1.51 g, 5.96 mmol). A saturated Na2S2O3 aqueous solution was added, and the mixture was extracted with ether. The organic layer was washed with brine, dried over MgSO4, filtered, and concentrated under reduced pressure. The crude product was subjected to a silica gel column chromatography with hexane as an eluent (Rf = 0.29), and was purified by recrystalization from hexane to give 225.2 mg (0.77 mmol) of bis-silicon-bridged stilbene (R = H, R0 = Me) in 39% yield. Table 1 Synthesis of bis-silicon-bridged stilbene by one-pot procedure
R
X
R0
Yield (%) a
H H H OMe OMe F
H OEt H OEt H H
Me Me Ph Me Hexyl Hexyl
43 39 40 62 68 48
a
Data in parentheses are the overall yield prepared by two-step method and based on bis(2-bromophenyl)acetylenes. See Refs. [4–7].
(47) (44) (33) (68) (72) (56)
1438
C.H. Li et al. / Chinese Chemical Letters 18 (2007) 1436–1438
2. Results and discussion For comparison, the yields of bis-silicon-bridged stilbene derivatives that prepared from the one-pot procedure and previous two steps method were given in Table 1, respectively. It can be shown, calculated from acetylene starting materials, the yields of bis-silicon-bridged stilbenes produced from the one pot synthesis are similar to the overall yields produced by the two-step method. These results demonstrate good tolerance of reaction conditions in the intramolecular reductive double cyclization. The existence of some impurities, such as lithium chloride as byproduct, and NH4Cl, as catalyst in the first step, shows negligible effect on the yield of bis-silicon-bridged stilbene derivatives. Acknowledgment We gratefully acknowledge the financial support of the National Natural Science Foundation of China (No. 50673094). References [1] [2] [3] [4] [5] [6] [7]
M.D. Watson, A. Fechtenko¨tter, K. Mu¨llen, Chem. Rev. 101 (2001) 1267. H.E. Katz, Z. Bao, S.L. Gilat, Acc. Chem. Res. 34 (2001) 359. M. Bendikov, D.F. Perepichka, F. Wudl, Chem. Rev. 104 (2004) 4891. S. Yamaguchi, C. Xu, K. Tamao, J. Am. Chem. Soc. 125 (2003) 13662. S. Yamaguchi, C. Xu, H. Yamada, A. Wakamiya, J. Organomet. Chem. 690 (2006) 5365. S. Yamaguchi, C. Xu, J. Org. Syn. Chem. Jpn. 63 (2006) 1115. C. Xu, H. Yamada, A. Wakamiya, S. Yamaguchi, K. Tamao, Macromolecules 37 (2004) 8978.
Chinese Chemical Letters 18 (2007) 1436–1438 www.elsevier.com/locate/cclet
One pot synthesis of bis-silicon-bridged stilbene derivatives Chen Hui Li a, Hua Yu Qiu a, Cai Hong Xu b,* a
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Teachers College, Hangzhou 310012, China b Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China Received 24 July 2007
Abstract Bis-silicon-bridged stilbene derivatives were synthesized in a modified procedure that combined the preparation of bis[2(silyl)phenyl]acetylene and its intramolecular reductive cyclization in one pot. The results indicated that the one pot approach produced target products in a comparable yield to that of the two-step method reported previously. # 2007 Cai Hong Xu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Bis-silicon-bridged stilbene; Reductive cyclization; One pot synthesis
Ladder p-conjugated molecules have attracted considerable attention in the past decades, due to their fascinating properties relating to organic electronics and optoelectronics [1–3]. As a fundamental skeleton of new ladder pconjugated systems, we have focused our attention on silicon-bridge containing frameworks. Recently we have reported a facile and effective synthesis of bis-silicon-bridged stilbene homologues via a newly developed intramolecular reductive cyclization reaction [4–7]. The bis-silicon-bridged stilbene derivatives were synthesized via two-step reactions. The first one is preparation of bis[2-(silyl)phenyl]acetylenes from metalation and followed silylation of bis(2-bromophenyl)acetylene. Then the isolated bis[2-(silyl)phenyl]acetylenes further undergoes intramolecular reductive cyclization with lithium naphthalenide (LiNaph) as reductant and iodine as quenching agent to produce target molecules. In this work, we have combined the preparation of bis[2-(silyl)phenyl]acetylene and its intramolecular reductive cyclization in one pot procedure as shown in Scheme 1. This approach produced target products in a comparable yield to that of the two-step method reported previously. 1. Experimental 1
H and 13C nuclear magnetic resonance (NMR) spectra were recorded in CDCl3 solution with a Bruker WM 300 spectrometer. Elemental analysis for C and H were determined with Carlo Erba 1106 analyzer. Thin-layer chromatography (TLC) was performed on plates coated with 0.2 mm thick silica gel. Column chromatography was performed using silica gel as a stationary phase (200–300 mesh). All experiments were carried out under a nitrogen atmosphere. THF was distilled from sodium/benzophenone prior to use. All other chemicals were purchased from Aldrich or Acros and used as received. * Corresponding author. E-mail address: [email protected] (C.H. Xu). 1001-8417/$ – see front matter # 2007 Cai Hong Xu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2007.09.039
C.H. Li et al. / Chinese Chemical Letters 18 (2007) 1436–1438
1437
Scheme 1. .
1.1. Synthesis of bis-dimethylsilylene-bridged stilbene using HMe2SiCl for silylation To a solution of bis(2-bromophenyl)acetylene (0.43 g, 1.28 mmol) in THF (15 mL) was added hexane solution of n-BuLi (1.6 mol/L, 1.7 mL, 2.72 mmol) dropwise at 78 8C. After stirred for 1.5 h, HMe2SiCl (0.4 mL, 3.60 mmol) was added via syringe at the same temperature. The mixture was gradually warmed to room temperature with stirring over 7 h. Then the resulting mixture was added to the solution of lithium naphthalenide prepared from granular lithium (35.8 mg, 5.16 mmol) and naphthalene (661.4 mg, 5.16 mmol) in THF (4 mL). After stirred for 5 min, the reaction mixture was quenched with a THF (5 mL) solution of iodine (1.31 g, 5.16 mmol). A saturated Na2S2O3 aqueous solution was added, and the mixture was extracted with ether. The organic layer was washed with brine, dried over MgSO4, filtered, and concentrated under reduced pressure. The crude product was subjected to a silica gel column chromatography with hexane as an eluent (Rf = 0.29), and was purified by recrystalization from hexane to give 160.9 mg (0.55 mmol) of bis-silicon-bridged stilbene (R = H, R0 = Me) in 43% yield [4]. 1.2. Synthesis of bis-dimethylsilylene-bridged stilbene using Me2(NEt2)SiCl for silylation To a solution of bis(2-bromophenyl)acetylene (0.50 g, 1.49 mmol) in THF (15 mL) was added a hexane solution of n-BuLi (1.6 mol/L, 1.9 mL, 3.04 mmol) dropwise at 78 8C. After stirred for 1 h, Me2(NEt2)SiCl (0.51 g, 3.08 mmol) was added via syringe at the same temperature and the mixture was allowed to warm to room temperature over 8 h under stirring. Ethanol (0.2 mL, 3.42 mmol) and NH4Cl (18 mg, 0.34 mmol) were added to the resulting mixture under nitrogen stream, followed by stirring for 11 h. Then the resulting mixture was added to the solution of lithium naphthalenide prepared from granular lithium (41.4 mg, 5.97 mmol) and naphthalene (763.9 mg, 5.96 mmol) in THF (5 mL). After stirred for 5 min, the reaction mixture was quenched with a THF (5 mL) solution of iodine (1.51 g, 5.96 mmol). A saturated Na2S2O3 aqueous solution was added, and the mixture was extracted with ether. The organic layer was washed with brine, dried over MgSO4, filtered, and concentrated under reduced pressure. The crude product was subjected to a silica gel column chromatography with hexane as an eluent (Rf = 0.29), and was purified by recrystalization from hexane to give 225.2 mg (0.77 mmol) of bis-silicon-bridged stilbene (R = H, R0 = Me) in 39% yield. Table 1 Synthesis of bis-silicon-bridged stilbene by one-pot procedure
R
X
R0
Yield (%) a
H H H OMe OMe F
H OEt H OEt H H
Me Me Ph Me Hexyl Hexyl
43 39 40 62 68 48
a
Data in parentheses are the overall yield prepared by two-step method and based on bis(2-bromophenyl)acetylenes. See Refs. [4–7].
(47) (44) (33) (68) (72) (56)
1438
C.H. Li et al. / Chinese Chemical Letters 18 (2007) 1436–1438
2. Results and discussion For comparison, the yields of bis-silicon-bridged stilbene derivatives that prepared from the one-pot procedure and previous two steps method were given in Table 1, respectively. It can be shown, calculated from acetylene starting materials, the yields of bis-silicon-bridged stilbenes produced from the one pot synthesis are similar to the overall yields produced by the two-step method. These results demonstrate good tolerance of reaction conditions in the intramolecular reductive double cyclization. The existence of some impurities, such as lithium chloride as byproduct, and NH4Cl, as catalyst in the first step, shows negligible effect on the yield of bis-silicon-bridged stilbene derivatives. Acknowledgment We gratefully acknowledge the financial support of the National Natural Science Foundation of China (No. 50673094). References [1] [2] [3] [4] [5] [6] [7]
M.D. Watson, A. Fechtenko¨tter, K. Mu¨llen, Chem. Rev. 101 (2001) 1267. H.E. Katz, Z. Bao, S.L. Gilat, Acc. Chem. Res. 34 (2001) 359. M. Bendikov, D.F. Perepichka, F. Wudl, Chem. Rev. 104 (2004) 4891. S. Yamaguchi, C. Xu, K. Tamao, J. Am. Chem. Soc. 125 (2003) 13662. S. Yamaguchi, C. Xu, H. Yamada, A. Wakamiya, J. Organomet. Chem. 690 (2006) 5365. S. Yamaguchi, C. Xu, J. Org. Syn. Chem. Jpn. 63 (2006) 1115. C. Xu, H. Yamada, A. Wakamiya, S. Yamaguchi, K. Tamao, Macromolecules 37 (2004) 8978.