synthesis and properties of brominated...

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* E-mail: [email protected], [email protected]; Tel.: 0086-022-23509933 Received November 16, 2009; revised March 2, 2010; accepted March 26, 2010.

Project supported by the National Natural Science Foundation of China (Nos. 20602020, 20971071).

1240 © 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Chin. J. Chem. 2010, 28, 1240—1246

Synthesis and Properties of Brominated 6,6'-Dimethyl-[2,2'-bi- 1H-indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-diones

Chen, Yonga,b(陈勇) Pang, Meili*,a(庞美丽) Cheng, Kaigea(程凯歌) Wang, Yinga(王英) Han, Jiea(韩杰) Meng, Jiben*,a(孟继本)

a Department of Chemistry, Nankai University, Tianjin 300071, China b Department of Chemistry, Anyang Normal University, Anyang, Henan 455002, China

Photochromic 6-bromomethyl-6'-methyl-[2,2'-bi-1H-indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-dione (2), 6,6'- bis(bromomethyl)-[2,2'-bi-1H-indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-dione (3) and 6,6'-bis(dibromomethyl)-[2,2'- bi-1H-indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-dione (4) have been synthesized from 6,6'-dimethyl-[2,2'-bi-1H- indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-dione (1). The single crystal of 4 was obtained and its crystal structure was analyzed. The results indicate that in crystal 4, molecular arrangement is defective tightness compared with its pre-cursor 1. Besides, UV-Vis absorption spectra in CH2Cl2 solution, photochromic and photomagnetic properties in solid state of 2, 3 and 4 were also investigated. The results demonstrate that when the hydrogen atoms in the methyl group on the benzene rings of biindenylidenedione were substituted by bromines, its properties could be affected considerably.

Keywords synthesis, brominated reaction, crystal structure, photochromism, photomagnetism

Introduction

In the past decades, a great number of organic photochromic compounds have been synthesized, but only a few of them have been found to possess photochromic property in solid state. Compared with a larger number of photochromic ones only in solution, solid-state or-ganic photochromic compounds not only have potential application in various optoelectronic devices such as high-density information storage systems, optical mem-ory, light-driven information display devices, optical calculation, and so on,1-7 but also might be used to gain control over other physical properties in the solid state due to the photo-induced molecular reversible transfor-mations.8-10 Typical examples include N-salicylid-ene-anilines,11,12 triarylimidazole dimmers,13,14 aziridi-nes,15 diarylperfluorocyclopentenes,16 diarylethenes,17 and biindenylidenedione derivatives.18 Among them, the biindenylidenedione derivatives are a class of unique photochromic compounds, which simultaneously gener-ate stable radicals and undergo photochromism in the crystalline state.19-25 This property is particularly prom-ising for their potential utility in optoelectronic devices. In order to explore the relationship between the struc-ture and physical properties such as photochromic and photomagnetic ones, we have continuously made modi-fications on biindenylidenedione backbone, and pre-pared a series of biindenylidenedione derivatives.21-28 Most of the structural modifications have been carried

out on the five-membered rings of the biindenylidenedione, and the results showed that such modifications have a considerable effect on both photochromic and photomagnetic properties of this kind of molecules in the solid state.22-28 At the same time, the attempts to introduce other substituents rather than hydrogen on the benzene rings in the biindenylidenedione have been made. For example, new methyl substituted biinde-nylidenedione derivatives dimethyl-[2,2'-bi-1H-indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-diones from 4- methylphthalic anhydride have been successfully syn-thesized,26 and their crystal structures and properties were also investigated. The results reveal that the sub-stituents, even like the simple methyl, on the benzene rings of biindenylidenedione could considerably affect the photochromic property, as well as other properties of this kind of compounds. In order to further investi-gate substituents effect on the benzene rings of biinde-nylidenediones, 6,6'-dimethyl-[2,2'-bi-1H-indene]-3,3'- diethyl-3,3'-dihydroxy-1,1'-dione (1) was brominated with N-bromosuccinimide (NBS) under photoirradiation to yield 6-bromomethyl-6'-methyl-[2,2'-bi-1H-indene]- 3,3'-diethyl-3,3'-dihydroxy-1,1'-dione (2), 6,6'-bis(bromomethyl-[2,2'-bi-1H-indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-dione (3) and 6,6'-bis(dibromomethyl)-[2,2'-bi- 1H-indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-dione (4), respectively (Scheme 1). The results demonstrate that when the hydrogen atoms in the methyl group on the benzene rings of biindenylidenedione were substituted

Brominated 6,6'-Dimethyl-[2,2'-bi-1H-indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-diones

Chin. J. Chem. 2010, 28, 1240—1246 © 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cjc.wiley-vch.de 1241

Scheme 1 The synthetic route for title compounds 2, 3 and 4

by bromines, its properties could be affected considera-bly. Herein, we report the results of our investigation.

Results and discussion

Crystal structure studies for compound 4

In order to obtain the single crystal of compounds 2—4, we have tried many ways. At last, only the single crystal of compound 4 was obtained successfully from slow evaporation of its CH2Cl2 solution at room tem-perature. The crystal structure data of compound 4 are available from the Cambridge crystallographic Data Center, CCDC Nos. (CCDC 655852). The X-ray dif-fraction data were collected at 113(2) K using graphite monochromated Mo Kα (λ＝0.71070 Å) on a BRUKER SMART1000 diffractometer. The structure solution and refinement were carried out using the programs SHELXS97 (Sheldric, 1990) and SHELXS97 (Sheldric, 1997). The crystal data and structure refinement details for compound 4 are given in Table 1. Selected bond lengths and bond angles are listed in Table 2.

The structure analysis reveals that compound 4 crystallizes in the triclinic space group p-1, with one molecule per unit cell (Figure 1), and its molecular structure is perfectly center symmetry (Figure 2). Com-pared with starting material compound 1 (Figure 3), the double bond length [C(1)—C(1A)＝1.368(18) Å] and the single bond length [C(9)—C(12)＝1.517(13) Å] in compound 4 are slightly longer than the corresponding bond length [1.354(4) and 1.503(3) Å, respectively] of compound 1.26 In ab-plane of crystal 4, the molecules are arranged side-by-side to form layers, and in each layer, molecules connect with each other through inter-molecular H-bonding [the H-bonding length C(5)—

O(2)…H(11A)—C(11A) is 2.625 Å] (Figures 4 and 5). Between adjacent molecular layers, molecules connect with each other through weak intermolecular H-bonding [the H-bonding length O(1)—H(1)…Br(2) is 2.679 Å],

and adjacent molecular benzene ring parallel arrange in offset face to face. The distance of centroid-centroid of benzene ring of adjacent molecules is 5.980 Å (Figure 4, Figure 5). The distance between benzene rings of adja-cent two molecular layers is too long to any possible intermolecular π-π stacking interaction, so in crystal 4, molecular arrangement is defectively tight compared with its precursor 1. The lower melting point (180—182

Table 1 Some selected crystallographic data for compound 4

Empirical formula C24H20O4Br4

Formula weigh 692.03

Crystal system Triclinic

Space group P-1

Unit cell dimensions a＝8.9793(7) Å, α＝64.949(19)°

b＝9.0466(7) Å, β＝63.37(2)°

c＝9.2896(8) Å, γ＝66.781(19)°

Volume/Å3 591.31(8)

Z 1

Calcd density 1.870 g•cm－3

Reflections collected 4872

Unique reflections 2283 [Rint＝0.0570]

Final R indices [I＞2σ(I)] R1＝0.0574, wR2＝0.1488

R indices (all data) R1＝0.0916, wR2＝0.2310

Absorption coefficient 6.831 mm－1

F(000) 322

Crystal size 0.06 mm×0.05 mm×0.04 mm

θ range for data collection 2.57°－26.00°

Limiting indices － 11≤ h≤ 11, － 11≤ k≤ 10,－11≤1＜11

Max. and min. transmission 0.7718 and 0.6847

Refinement method Full-matrix least-squares on F2

Data/restraints/parameters 2283/7/150

Largest diff. peak and hole 1.886 and －1.252 e•A－3

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Table 2 Selected bond distances (Å), angles (°) and torsion angles (°) for 4

Bond length Bond angle Torsion angle

Br(1)—C(12) 1.934(10) C(1A)-C(1)-C(5) 125.2(10) C(1A)-C(1)-C(2)-O(1) －53.6(15)

Br(2)—C(12) 2.012(10) O(1)-C(2)-C(1) 114.8(8) C(1A)-C(1)-C(2)-C(13) －168.8(12)

O(1)—C(2) 1.420(12) O(1)-C(2)-C(6) 110.2(7) C(3)-C(8)-C(9)-C(12) －176.1(9)

C(1)—C(1A) 1.368(18) O(2)-C(5)-C(1) 126.7(8) C(10)-C(9)-C(12)-Br(1) 155.8(7)

O(2)—C(5) 1.249(10) C(5)-C(9)-C(12) 121.9(8) C(10)-C(9)-C(12)-Br(2) －83.7(9)

C(9)—C(12) 1.517(13) Br(1)-C(12)-Br(2) 107.7(4) C(5)-C(1)-C(2)-O(1) 123.7(8)

O(1)—H(1) 0.83(3) O(1)-C(2)-C(3) 1.6.1(7) C(5)-C(1)-C(2)-C(3) 8.5(9)

C(1)—C*(5) 1.516(12) C(3)-C(2)-C(6) 110.5(7) C(5)-C(1)-C(2)-C(6) －110.3(8)

C(2)—C(6) 1.565(12) C(1)-C(2)-C(6) 111.3(7) O(1)-C(2)-C(3)-C(8) 56.8(12)

C(6)—C(7) 1.532(15) C(8)-C(3)-C(4) 120.7(8) C(1)-C(2)-C(3)-C(8) 178.1(9)

C(4)—C(5) 1.471(12) C(9)-C(12)-Br(1) 115.1(7) O(1)-C(1)-C(2)-C(4) －124.5(8)

C(9)-C(12)-Br(2) 108.4(7) C(9)-C(10)-C(11)-C(4) 4.4(16)

Figure 1 Single crystal structure of compound 4.

Figure 2 Molecular structure and atom numbering scheme for compound 4.

Figure 3 Molecular structure of 1.

℃) of 4 may be owing to the lack ofπ-π stacking inter-action, and its crystal structure is defective tightness compared with compound 1 (269—271 ℃).26 The melting point of compounds 2 (240—242 ℃) and 3

Figure 4 Display of H-bonding interactions for compound 4.

Figure 5 Expanded crystal packing diagram for compound 4.

(261—262 ℃) are also lower compared to compound 1, this might be due to that in solid compounds 2 and 3, molecular arrange is not so tight compared with their precursor 1 although we have not obtained the single crystals of compounds 3 and 4. The inducement of this phenomenon is considerablely due to that the hydrogen atoms in the methyl groups on the benzene rings of bi-indenylidenedione are substituted by bromines.



UV-Vis absorption spectra in solution

UV-Vis absorption peaks and coefficients of com-pounds 2—4 in CH2Cl2 solution are listed in Figure 6 and Table 3. Compounds 2—4 have all two absorption peaks: one is at 234—239 nm; the other is at 319—338 nm. For compounds 2 and 3, the absorption peak strength of long-wavelength band [λmax＝338 nm (2), λmax＝327.5 nm (3)] is more intense than that of short-wavelength band [λmax＝234 nm (2), λmax＝237 nm (3)], which is similar to their precursor compound 1.26 While for compound 4, the absorption peak strength of long-wavelength band (λmax＝319 nm) is less intense than that of short-wavelength band (λmax＝239 nm). For short-wavelength band, from compound 2 to 4, the λmax

increase in turn [234 nm (2), 237 nm (3), and 239 nm (4), respectively], and their λmax are longer than that of compound 1 (λmax＝229.2 nm). For long-wavelength band, from compound 2 to 4, λmax decreases in turn [338 nm (2), 327.5 nm (3), and 319 nm (4), respectively], and their λmax are shorter than that of their precursor com-pound 1 (λmax＝340.8 nm).26 From 1 to 4, the hydrogen atoms in the methyl groups on the benzene rings of biindenylidenedione are substituted by 0, 1, 2, 4 bromo atoms in turn (compound 1, electron-donating CH3; compound 2, one CH2Br group; compound 3, two CH2Br groups; compound 4, two electron with drawing CHBr2 groups). We presume these results are due to the introducing of electron-withdrawing bromo atoms.

Figure 6 UV-Vis absorption spectra of compounds 2 (a) 3 (b) and 4 (c) in CH2Cl2 solution.

Photochromic property in solid state

All compounds 2—4 possess visible photochromism upon irradiation with high pressure Hg lamp. Their color changes after photoirradiation are listed in Table 4. In consistency with our previous observation,21-26 their UV-Vis absorption considerably increases in the wave-length range of 500—800 nm after irradiation with high pressure Hg lamp as illustrated in Figure 7. These ob-servations confirm that the compounds 2—4 are photo-chromic as expected. The photochromic mechanism of 4 is proposed in Scheme 2. The yellow-green solid pow-der of 4a turns to dark-blue 4b upon irradiation with

Table 3 UV-Vis absorption maxima and coefficients of com-pounds 2—4 in CH2Cl2 solution

Compound λmax/nm (ε) c/(mol•L－1)

2 234 (13983), 338 (22032) 2.2×10－5

3 237 (18447), 327.5 (25068) 2.2×10－5

4 239 (25465), 319 (22576) 1.5×10－5

Table 4 The color changes of compounds 2—4 before and after irradiation with high pressure Hg lamp in the solid state

Compd. 2 3 4

Before photoirradiation

Orange Orange Yellow-green Color

After photoirradiation

Brick-red Grey-green Dark-blue

Scheme 2 The photochromic mechanism of compound 4

high Hg lamp for 10 min; 4b is thermally labile, and the dark-blue solid powder returns to the original yel-low-green quickly upon heating.

ESR spectra

As identified previously,21-26 biindenylidenedione derivatives simultaneously generate radicals while un-dergoing photochromism. Hence, ESR technique could provide solid evidence for the existence of radical spe-cies upon photochromism. Before photoirradiation, compounds 2—4 do not show ESR signals in solid state at room temperature; after photoirradiation, they show ESR signals in solid state at room temperature (Figure 8). The characteristic values of ESR signals are as fol-lows: 2 (g＝2.0030, ∆Hpp＝7.3313), 3 (g＝2.0026, ∆Hpp

＝17.59546), 4 (g＝2.0026, ∆Hpp＝14.66284), respec-tively. By comparison with their precursor 1, the char-acteristic values of ESR signals of 2—4 show consider-able differences. For example, ∆Hpp of compounds 2—4 (especially compounds 3 and 4) are considerably larger than their precursors' (1, ∆Hpp＝7.03809).26 We pre-sume these results are due to that the amount of elec-tron-withdrawing bromo atoms increases in turn from compound 1 to 4. When the irradiated 2—4 were dis-solved in dichloromethane, the resulting solutions did not show any ESR signal and photochromism. The re-sults indicated clearly that the radicals generated from two indanione moieties are quenched in the solution.



Figure 7 The changes of UV-Vis spectra of compounds 2 (a), 3 (b) and 4 (c) before and after irradiation with high pressure Hg lamp in the solid state.

Experimental

Materials and instruments

All chemicals were purchased from commercial sources, and solvents were dried by refluxing over an appropriate drying agent and distilled prior to use. Melting points were determined with Yanagimoto MP-35 melting point apparatus and uncorrected. 1H NMR spectra were recorded on BRUKER AC-P300. UV-Vis spectra were recorded on Schimadzu UV-

Figure 8 ESR spectra of compounds 2—4 upon irradiation with high pressure Hg lamp in the solid state at room temperature (work frequency, 9.858 GHz).

2101PC UV-Vis spectrophotometer. The mass spectra were recorded on Thermo Finnigan LCQ Advantage spectrometer in ESI mode-I with spray voltage 4.8 kV. Infrared spectra were recorded on a NICOLET-380- FT-IR spectrophotometer. A Yamaco CHN CORDER MT-3 apparatus was used for elemental analysis. The X-ray diffraction data were collected using Mo Kα ra-diation (λ＝0.71073 Å) on a BRUKER SMART 1000 diffractometer. The powder ESR spectra were recorded using a Bruker A-320 EPR spectrometer.

Synthesis and characterization

The synthetic route for title compounds 2—4 are



shown in Scheme 1. The starting material 1 was pre-pared according to our reported literature26 and its structure was confirmed by the X-ray crystallography (Figure 3). Data for 1 were collected using Mo Kα ra-diation (λ＝0.71073 Å) at 294(2) K. Empirical formula C24H24O4, formula weight 376.43, monoclinic, space group P2(1)/n, a＝8.571(4) Å, b＝7.472(3) Å, c＝15.531(6) Å, α＝90°, β＝100.566(6)°, γ＝90°, V＝977.8(7) Å3, Z＝2, d(calc)＝1.279 g•cm－3, reflection collected/unique 5034/2014 [R(int)＝0.0552], final R indices [I＞2σ(I)] R1＝0.0538, wR2＝0.1327, R indices (all data) R1＝ 0.1067, wR＝ 0.1584, GOF＝ 1.004, CCDC 627737.

Synthesis of 6-bromomethyl-6'-methyl-[2,2'-bi-1H- indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-dione (2)

Compound 1 (1.000 g, 2.66 mmol), N-bromosuccinimide (1.000 g, 5.62 mmol) and benzoyl peroxide (30 mg) in 80 mL dry benzene were irradiated with in-candescent light and refluxed for 10 h. The solvent was then removed under reduced pressure, the solid residue was obtained, which was further purified by column chromatography (silica, V(hexane)∶V(EtOAc)∶V(dichloromethane)＝50∶6∶1). Compound 2 was ob-tained as orange solid (0.472 g, 39%). m.p. 240—242 ℃; 1H NMR (CDCl3, 300 MHz) δ: 0.55—0.58 (t, J＝15 Hz, 6H, CH2CH3), 2.14—2.28 (m, 4H, CH2CH3), 2.54 (s, 3H, ArCH3), 4.58 (s, 2H, ArCH2Br), 6.60 (s, 1H, OH), 6.77(s, 1H, OH), 7.35—7.86 (m, 6H, ArH); MS (ESI) m/z: 455.33 [M－1]; IR (KB): 1054, 1216, 1283, 1400, 1450, 1607, 1663, 2932, 2966, 3352 cm－1. Anal. calcd for C24H23BrO4: C 63.31, H 5.09; found C 63.37, H 5.05.

Synthesis of 6,6'-bis(bromomethy)l-[2,2'-bi-1H- indene]-3,3'-diethyl-3,3'-dihydroxy -1,1'-dione (3)

Compound 1 (1.000 g, 2.66 mmol), N-bromosuccinimide (1.500 g, 8.43 mmol) and benzoyl peroxide (30 mg) in 80 mL dry benzene were irradiated with in-candescent light and refluxed for 15 h. The solvent was then removed under reduced pressure, and the solid resi-due was obtained, which was further purified by column chromatography (silica, V(hexane)∶V(EtOAc)∶V(dichloromethane)＝50∶6∶1). 3 was obtained as orange solid (0.302 g, 21%). m.p. 261—262 ; ℃

1H NMR (CDCl3, 300 MHz) δ: 0.55—0.60 (t, J＝15 Hz, 6H, CH2CH3), 2.14—2.28 (m, 4H, CH2CH3), 4.58 (s, 4H, ArCH2Br), 6.59 (s, 2H, OH), 7.58—7.91 (m, 6H, ArH); MS (ESI) m/z: 533.2 [M－1]; IR (KB): 1048, 1221, 1289, 1395, 1450, 1602, 1675, 1714, 2927, 2966, 3340 cm－1. Anal. calcd for C24H22Br2O4: C 53.96, H 4.15; found C 53.91, H, 4.19.

Synthesis of 6,6'-bis(dibromomethyl)-[2,2'-bi-1H- indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-dione (4)

Compound 1 (1.000 g, 2.66 mmol), N-bromosuccinimide (2.500 g, 14.04 mmol) and benzoyl peroxide (30 mg) in 80 mL dry benzene were irradiated with in-candescent light and refluxed for 90 h. The solvent was

then removed under reduced pressure, and the solid residue was obtained, which was crystallized from di-chloromethane to give 4 as yellow-green solid (0.860 g, 49%). m.p. 180—182 ; ℃

1H NMR (CDCl3, 300 MHz) δ: 0.58—0.63 (t, J＝15 Hz, 6H, CH2CH3), 2.15—2.32 (m, 4H, CH2CH3), 6.53 (s, 2H, ArCHBr2), 6.72 (s, 2H, OH), 7.82—7.91 (m, 6H, ArH); MS (ESI) m/z: 690.9 [M－1]; IR (KB): 1051, 1217, 1395, 1607, 1669, 1719, 2934, 2963, 3386 cm－1. Anal. calcd for C24H20Br4O4: C 41.65, H 2.91; found C 41.58, H 2.87.

Conclusion

In this work, 6-bromomethyl-6'-methyl-[2,2'-bi-1H- indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-dione (2), 6,6'- bis(bromomethyl)-[2,2'-bi-1H-indene]-3,3'-diethyl-3,3'- dihydroxy-1,1'-dione (3), and 6,6'-bis(dibromomethyl)- [2,2'-bi-1H-indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'- dione (4) were synthesized from 6,6'-dimethyl-[2,2'- bi-1H-indene]-3,3'-diethyl-3,3'-dihydroxy-1,1'-dione (1). The single crystal of 4 was obtained and its crystal structure was analyzed. The results indicate that in crystal 4, molecular arrangement is defectively tight compared with its precursor 1. The UV-Vis absorption spectra in CH2Cl2 solution, photochromic and pho-tomagnetic properties in solid state of 2—4 were inves-tigated. The results reveal that in CH2Cl2 solution, for short-wavelength band, from compound 2 to 4, λmax in-crease, while for long-wavelength band, from com-pound 2 to 4, λmax decrease. After photoirradiation, the color of compounds 2—4 in solid state changed, and at the same time, ESR spectra (∆Hpp) of 2—4 in solid state showed an obvious different signal. All of these results demonstrate when the hydrogen atoms in the methyl group on the benzene rings of biindenylidenedione are substituted by bromines, its properties could be affected considerably.

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