5 J Chem Res April 2009

244

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RESEARCH PAPER

JOURNAL OF CHEMICAL RESEARCH 2009

Synthesis of polymethyl substituted [2.2]metaparacyclophanes and their Lewis-acid induced isomerisation to [2.2]metacyclophanes Tomoe Shimizua, Katsuhiro Hitaa, Arjun Paudela, Junnji Tanakab and Takehiko Yamatoa,* aDepartment bInstitute

of Applied Chemistry, Faculty of Science and Engineering, Saga University, Honjo-machi 1, Saga 840-8502, Japan

for Material Chemistry and Engineering, Kyushu University, 6-1, Kasugakoen, Kasuga 816-8580, Japan

The preparation of polymethyl substituted [2.2]metaparacyclophanes using sulfur method and the X-ray structure determination of 4,5,6,8,12,13,15,16-octamethyl[2.2]metaparacyclophane are described. AlCl3-MeNO2-catalysed trans-tert-butylation of 5-tert-butyl-8,12,13,15,16-pentamethyl[2.2]metaparacyclophane in benzene led to isomerisation reaction to afford the strainless 8,12,13,14,16-pentamethyl[2.2]metacyclophane in 85% yield along with tert-butylbenzene.

Keywords: metacyclophane, metaparacyclophane, Lewis-acid, isomerisation, strain The meta-bridged benzene ring of [2.2]metaparacyclophane (MPCP = metaparacyclophane) (1) has been shown to undergo FRQIRUPDWLRQDOÀLSSLQJ±with a substantial energy barrier (ca. 20 kcal mol-1). According to X-ray crystallographic studies of 1,8 the deformations of benzene rings are similar to those of the corresponding rings in para- and meta[2.2]cyclophanes, with para- and meta-bridged rings bent in a boat- and a chairlike form, respectively. The angle between the two aromatic SODQHV GH¿QHG E\ WKH FDUERQ DWRPV    DQG  RQ RQH hand, and 12, 13, 15 and 16, on the other, is about 13°. It should be noted that the angle between the 11, 12, 16-plane and 10, 11-bond vector (or between 13, 14, 15-plane and 1, 14-bond vector) is even larger than the analogous angle in [2.2]paracyclophane. The para-bridged moiety of 1 is thus more strongly tilted than those of the isomeric compound. Introduction of the substituents at the 8-position increases the strain in the molecule in comparison with the unsubstituted [2.2]MPCP (1); the deformation of para-benzene ring of 8methyl[2.2]MPCP (2) was estimated to 15° by our previous X-ray crystallography.9 Thus introduction of methyl group to the para benzene ring of [2.2]MPCP also increases the strain in the molecule. Therefore, there is substantial interest to prepare the polymethyl substituted [2.2]MPCPs to investigate the relationship between the strain and reactivity.10,11 Previously

Me ClCH2

Results and discussion

The preparative route of polymethyl substituted [2.2]MPCPs 8a and 8b is shown in Scheme 1. The preparation of 2,65 6

+

2

8 16

10

Me Me Me

1

14 13

12

2

1

Me

3

Me

Fig. 1

Me KOH/NaBH4

CH2SH

EtOH high dilution

Me 6

R1 R2

Me

15

11

Me

R1 4 a; R1= R2= Me b; R1= tBu, R2= H

3

9

HSCH2

R2

4

7

Me CH2Cl

R2

we found that 8-methyl- and 8-hydroxy[2.2]MPCPs9 can be conveniently prepared by AlCl3-MeNO2-catalysed trans-tertbutylation of the corresponding tert-butyl derivatives. These results suggest that 8,12,13,15,16-pentamethyl[2.2]MPCP (3) might be also prepared from the corresponding tert-butyl derivative, using the tert-butyl group as a positional protective group on aromatic ring.± We report here the convenient preparation of the title compounds and their treatment with Lewis acid catalyst in a benzene solution.

R1

R2

R2

5

R2

6

4 8

Me S Me

Me

Me S

P(OEt)3 hu

Me Me

Me

16

15

12

13

Me

Me

7 a; R1= R2= Me (68%) b; R1= tBu, R2= H (54%)

Me 8 a; R1= R2= Me (76%) b; R1= tBu, R2= H (71%)

Scheme 1

* Correspondent. E-mail: [email protected]

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JOURNAL OF CHEMICAL RESEARCH 2009 bis(chloromethyl)toluenes 4a and 4b has already been described previously.12,17 1,4-Bis(sulfanylmethyl)-2,3,5,6tetramethylbenzene 6 was prepared from the corresponding 1,4-bis(chloromethyl)-2,3,5,6-tetramethylbenzene 5 according the reported procedure.18 The cyclisation of bis(chloromethyl) benzenes 4a and 4b and bis(sulfanylmethyl)benzene 6 was carried out under highly diluted conditions in 10% ethanolic KOH in the presence of a small amount of NaBH4, giving the desired 2,11-dithia[3.3]MPCPs 7a and 7b in good yield. Photolysis of 7a and 7b with a high-pressure murcury lamp (400W) in triethylphosphate was carried out according to the reported method19,20 to afford the corresponding [2.2]MPCPs 8a and 8b in good yields, respectively. The structures of 8a and 8b were determined on the basis of their elemental analyses and spectral data. The 1H NMR spectrum of 8b in CDCl3 shows a singlet at G 1.74 ppm for methyl protons at 15,16-positions which is in a strongly shielding region of opposite meta-bridged benzene ring and G 2.31 ppm for external methyl protons at 12,13-positions, respectively. On the other hand, the signals of the internal methyl protons at 8-position and two aromatic protons for &DQG&ZHUHREVHUYHGDWXSSHU¿HOGRIG 1.75 and 6.63 ppm which is in a strongly shielding region of opposite parabridged benzene ring. X-ray crystallographic study of 8a shows that the compound is apparently conformationally more rigid than (1, R=H) because its methyl substituent at 8 position is likely impinge upon the electron cloud of the para-bridged one. It is quite interesting that the increase of degree of deformation of para-benzene ring, which was estimated to 18.84° of 8a compared with that of 2 to 15°. Introduction of the methyl groups at 12,13,15 and 16 positions increases the deformation of para-benzene ring. Thus introduction of methyl groups to the para benzene ring of [2.2]MPCP also increases the strain in the molecule in comparison with the unsubstituted 8-methyl[2.2]MPCP 2.9 It was also found the distortion angle of meta benzene ring from planality is 15.94° in comparison with that of 8,16-dimethyl[2.2]metacyclophane (17.18°).21,22 Attempted TiCl4-catalysed trans-tert-butylation of 8b in benzene carried out under various of conditions failed. Only the recovery of the starting compound 8b resulted. Interestingly, the AlCl3±0H122-catalysed trans-tert-butylation of 8b in

benzene at 50 °C for 3 h the afforded metacyclophanes 9 and 10 in 65 and 30% yields along with the formation of tertbutylbenzene 11. None of the expected product, 8,12,13,15,16pentamethyl[2.2]MPCP 3 was detected under the conditions used. Prolonged reaction for 12 h under the same conditions gave only 10 in 85% yield. This result suggests that 9 might be an intermediate in the formation of 10. Indeed, 10 was also obtained in good yield when 9 was treated with AlCl3±0H122 in benzene under the same reaction conditions (at 50 °C for 12 h). Thus, the present Lewis acid isomerisation was supposed to be much faster than trans-tert-butylation of 8b to afford 3. However, a similar catalytic treatment of 8a with AlCl3± MeNO2 in benzene at 50 °C for 12 h only afforded intractable mixture of products. The structures of the products 9 and 10 were determined from their elemental analyses and spectral data. The 1H NMR spectrum of 9 in CDCl3VKRZVDQXS¿HOGVKLIWRIWKHLQWHUQDO methyl protons at G 0.48 and 0.54 ppm due to the ring current effect23,24 of the opposite aromatic ring compared to those of original [2.2]MPCP 8a 7KH VLPLODU ¿QGLQJV ZHUH REVHUYHG in 10. These data strongly support the [2.2]metacyclophane structures 9 and 10.

Fig. 2 X-ray (ellipsoids) structure of 4,5,6,8,12,13,15,16octamethyl[2.2]MPCP 8a. The thermal ellipsoids are given at 50% probability.

tBu

AlCl3/MeNO2 8b

Me Me

Me

benzene 50°C for 3 h

tBu

tBu

Me Me

+

8b

+H+

Me

Me

Me

Me

Me

Me

+

+

Me

Me

Me

Me

3

245

H Me

Me

Me 9

H Me

Me B

A tBu

tBu Me Me

+

Me

Me

Me 10

Me C

Scheme 2

9

10

+

11 Me

-H+

Me Me

+

Me H

Scheme 3

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A mechanism for the formation of the isomerisation products 9 and 10 from 8b is tentatively proposed in Scheme 3. Cram et al. reported25 the AlCl3-catalysed isomerisation of [2.2]paracyclophane to the less strained [2.2]MPCP 1 along with transannular isomerisation products, 1,2,2a,3,4,5hexahydropyrene and [2.2]metacyclophane. In the case of 5-tert-butyl-8,12,13,15,16-pentamethyl[2.2]MPCP 8b, the protonation of the ipso-position of ethylene bridge on the parabenzene ring could afford the cation intermediate (A), which could isomerise to the strainless 5-tert-butyl-8,12,13,14,16pentamethyl[2.2]metacyclophane 9 via cation intermediates B and C. This novel isomerisation reaction might attributed to the methyl group at the 8-position of meta benzene ring and the methyl groups at the 12,13,15,16-positions of para benzene ring, which increase the strain in the molecule in comparison with the unsubstituted [2.2]MPCP 1 and 8-methyl[2.2]MPCP 2. We previously reported the AlCl3±0H122 catalysed trans-tert-butylation of 5-tert-butyl-8-methyl[2.2]MPCP afforded only the desired 8-methyl[2.2]MPCP 2.9 No present isomerisation reaction was observed under the conditions used. These results are attributable to the increase of degree of deformation of para-benzene ring, which was estimated to 18.84° by the X-ray crystallographic study of 8a compared with that of 1 to 13° and 2 to 15°. Finally, the trans-tertbutylation of compound 9 would give 8,12,13,14,16-pentamet hyl[2.2]metacyclophane 10. Conclusions

It is concluded that the above isomerisation reaction of 8methyl[2.2]MPCP to form 8-methyl[2.2]metacyclophane is strongly affected by the bulkiness of the methyl group in the 8-position of meta benzene ring and the methyl groups at the 12,13,15,16-positions of para benzene ring which increase the strain in the molecule. Further studies on the chemical properties of polymethyl substituted [2.2]MPCPs are now in progress. Experimental All melting points are uncorrected. 1H NMR spectra were recorded at 300 MHz on a Nippon Denshi JEOL FT-300 NMR spectrometer in deuteriochloroform with Me4Si as an internal reference. IR spectra were measured as KBr pellets on a Nippon Denshi JIR-AQ2OM spectrometer. Mass spectra were obtained on a Nippon Denshi JMSHX110A Ultrahigh Performance Mass Spectrometer at 75 eV using a direct-inlet system. Elemental analyses were performed by Yanaco MT-5. Materials: 2,6-Bis(chloromethyl)-4-tert-butyltoluene 4b12 and 1,4-bis(chloromethyl)-2,3,5,6-tetramethylbenzene 517 were prepared according to the literature. Preparation of 2,6-bis(chloromethyl)-1,3,4,5-tetramethylbenzene (4a): To a solution of 1,2,3,5-tetramethylbenzene (67.1 g, 0.5 mol) and chloromethyl methyl ether (150 mL) was added zinc chloride (40 g, 0.29 mol) at room temperature. After the reaction mixture was stirred for 10 min, it was poured into ice-water (300 mL) and extracted with CH2Cl2 (200 mL u 3). The CH2Cl2 extract was washed with saturated aqueous NaCl (100 mL u 2), water (200 mL) and dried (Na2SO4) and evaporated in vacuo to leave a colourless solid. Recrystallisation from hexane gave 4a as colourless prisms (88.0 g,  PS± °C (lit.17 114 °C). Preparation of 1,4-bis(sulfanylmethyl)-2,3,5,6-tetramethylbenzene (6): A solution of 1,4-bis(chloromethyl)-2,3,5,6-tetramethylbenzene 5 (9.25 g, 0.40 mmol) and thiourea (6.7 g, 88 mmol) in DMSO (50 mL) was stirred at room temperature under atmosphere of nitrogen for 14 h. After the reaction mixture was poured into a solution of NaOH J LQZDWHUP/ WKHVROXWLRQZDVVWLUUHGIRUKDFLGL¿HG with aqueous 10% HCl and extracted with CH2Cl2 (100 mL u 2). The CH2Cl2 extract was washed with water (100 mL) and saturated aqueous NaCl (100 mL), and dried (Na2SO4) and evaporated in vacuo to leave a colourless solid. Recrystallisation from hexane gave 6 DV FRORXUOHVV SULVPV  J   PS ± °C; Qmax/cm-1 (KBr) 3040, 2960, 2900, 2550, 1430, 1370, 1225, 1010, 790 and 675; GH (CDCl3) 1.56 (2H, t, J = 6.6 Hz, SH), 2.28 (12H, s, CH3) and 3.80 (4H, d, J = 6.6 Hz, CH2); m/z 226 (M+) (Found: C, 63.61; H, 8.13. C12H18S2 (226.4) requires C, 63.66; H, 8.01%).

Preparation of 5,6,7,9,14,15,17,18-octamethyl-2,11-dithia[3.3] metaparacyclophane (7a): A solution of 4a (5.27 g, 20 mmol) and 6 (4.52 g, 20 mmol) in benzene (100 mL) was added dropwise over a period of 12 h from a Hershberg funnel with stirring under nitrogen to a solution of potassium hydroxide (4.0 g, 71 mmol) and sodium borohydride (1 g) in ethanol (4 l). After the addition, the reaction mixture was concentrated and the residue was extracted with CH2Cl2 (200 mL u 2). The CH2Cl2 extract was concentrated and the residue was chromatographed on silica gel (Wako C-300, 400 g) (hexanebenzene, 1 : 1 v/v, as eluent) to give a colourless solid. Recrystallisation from hexane-benzene 1 : 1 (v/v) gave 5,6,7,9,14,15,17,18-octamethyl2,11-dithia[3.3]metaparacyclophane (7a) as colourless prisms (5.22 J PS± °C; GH (CDCl3) 1.74 (3H, s, CH3), 1.79 (6H, s, CH3), 2.12 (3H, s, CH3), 2.27 (6H, s, CH3), 2.36 (6H, s, CH3), 3.62 (2H, d, J = 16.2 Hz, CH2), 3.67 (2H, d, J = 13.7 Hz, CH2), 3.70 (2H, d, J = 16.2 Hz, CH2) and 4.34 (2H, d, J = 13.5 Hz, CH2); GC (CDCl3) 16.05, 16.21, 16.73, 17.88, 18.44, 30.12, 30.66, 129.43, 131.72, 132.69, 133.28, 133.39, 133.44 and 133.60; m/z 384 (M+) (Found: C, 75.05; H, 8.45. C24H32S2 (384.64) required C, 74.94; H, 8.39). Cyclisation reactions of 4b and 6 were carried out using the same procedure as described above to afford 7b. 6-tert-Butyl-9,14,15,17,18-pentamethyl-2,11-dithia[3.3]metaparacyclophane (7b &RORXUOHVVSULVPVJ PS± °C; GH (CDCl3) 1.32 (9H, s, tBu), 1.79 (3H, s, CH3), 1.89 (6H, s, CH3), 2.34 (6H, s, CH3), 3.50 (2H, d, J = 15.2 Hz, CH2), 3.61 (2H, d, J = 14.2 Hz, CH2), 3.62 (2H, d, J = 15.2 Hz, CH2), 4.25 (2H, d, J = 14.2 Hz, CH2) and 7.10 (2H, s, ArH); GC (CDCl3) 14.79. 16.44, 17.90. 30.76, 31.59. 32.24, 34.27, 124.90, 128.66, 131.91, 132.33, 133.80, 136.99 and 145.51; m/z 398 (M+) (Found: C, 75.46; H, 8.42. C25H34S2 (398.67) required C, 75.32; H, 8.6). 3KRWRO\VLV RI GLVXO¿GH 7a to give 4,5,6,8,12,13,14,16-octamethyl [2.2]metaparacyclophane (8a): A solution of 7a (480 mg, 1.25 mmol) in triethylphosphate (100 mL) was irradiated with a 100 W high pressure mercury lamp (Riko Kagaku Sangyo Co.) for 6 h at URRP WHPSHUDWXUH LQ DUJRQ DWRPRVSKHUH $ 3\UH[ ¿OWHU ZDV XVHG $IWHU WKH UHDFWLRQ PL[WXUH ZDV SRXUHG WR LFH± 1D2+ VROXWLRQ (200 mL), it was stirred at room temperature for 3 h and and extracted with CH2Cl2 (200 mL u 2). The CH2Cl2 extract was washed with water (100 mL), brine (100 mL) and dried (Na2SO4) and evaporated in vacuo to leave the residue. The residue was chromatographed on silica gel (Wako C-300, 400 g) (hexane as eluent) to give a colourless solid. Recrystallisation from hexane gave 4,5,6,8,12,13,14,16-octamethyl[2.2]metaparacyclophane (8a) as colourless prisms (304 mg,  PS± °C; GH (CDCl3) 1.61 (6H, s, CH3), 1.72 (3H, s, CH3), 2.07 (3H, s, CH3), 2.19 (6H, s, CH3), 2.31 (6H, s, CH3) and ± + P CH2); GC (CDCl3) 15.83, 15.98. 16.07, 16.26, 18.82, 26.85, 28.32, 129.38, 130.0, 130.5, 131.7, 133.9, 135.1 and 136.2; m/z 320 (M+) (Found: C, 90.13; H, 10.19. C24H32 (320.52) required C, 89.94; H, 10.06). Photolysis of 7b was carried out using the same procedure as described above to afford 8b in 71% yield. 5-tert-Butyl-8,12,13,15,16-pentamethyl[2.2]metaparacyclophane (8b  &RORXUOHVV SULVPV PS±ƒ& GH (CDCl3) 1.29 (9H, s, tBu), 1.74 (6H, s, CH3), 1.75 (3H, s, CH3), 2.31 (6H, s, CH3 ± 2.60 (2H, m, CH2 ±+PCH2 ±+PCH2) and 6.63 (2H, s, ArH); GC (CDCl3) 16.57, 16.89, 17.33, 29.67, 29.90, 32.20, 34.45, 123.41, 131.38, 132.35, 133.23, 135.76, 138.72, and 144.55; m/z 334 (M+) (Found: C, 89.73; H, 10.17. C25H34 (334.55) required C, 89.76; H,10.24). AlCl3-MeNO2 Catalysed trans-tert-butylation of 8b in benzene: To a solution of 8b (230 mg, 0.68 mmol) in benzene (30 mL) was added a solution of AlCl3 (27.2 mg, 0.204 mmol) in MeNO2 (0.05 ml). After the reaction mixture had been stirred for 3 h at 50 °C, it was poured into ice-water and extracted with ether (30 mL u 2). The ether extract was dried (Na2SO4) and concentrated under reduced pressure to leave the residue. The residue was chromatographed on silica gel (Wako C-300, 200 g) (hexane as eluent) to give 9 (148 mg, 65%) and 10 (57 mg, 30%) as a colourless solid, respectively. The formation of tert-butylbenzene (11 ZDVFRQ¿UPHGE\*/& 5-tert-Butyl-8,12,13,15,16-pentamethyl[2.2]metacyclophane (9): &RORXUOHVVSULVPVKH[DQH PS±ƒ&GH (CDCl3) 0.48 (3H, s, CH3), 0.54 (3H, s, CH3), 1.29 (9H, s, tBu), 2.15 (3H, s, CH3), 2.31 (6H, s, CH3  ± + P CH2  ± + P CH2), ± + P CH2  ± + P CH2) and 7.12 (2H, s, ArH); GC (CDCl3) 14.07, 15.42, 14.44, 31.41, 32.51, 33.93, 34.91, 123.88, 129.70, 131.77, 132.63, 136.89, 139.15, 139.26 and 146.88; m/z 334 (M+) (Found: C, 89.68; H, 10.15. C25H34 (334.55) required C, 89.76; H,10.24).

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JOURNAL OF CHEMICAL RESEARCH 2009 8,12,13,15,16-Pentamethyl[2.2]metacyclophane (10): Colourless SULVPV KH[DQH  PS± °C; GH (CDCl3) 0.48 (3H, s, CH3), 0.49 (3H, s, CH3), 2.16 (3H, s, CH3), 2.32 (6H, s, CH3), 2.50 (2H, ddd, J = 4.5, 12.0, 13.1 Hz, CH2), 2.70 (2H, ddd, J = 3.9, 12.0, 12.2 Hz, CH2), 2.84 (2H, ddd, J = 3.0, 4.5, 12.5 Hz, CH2), 3.26 (2H, ddd, J = 3.0, 3.9, 13.1 Hz, CH2), 6.87 (1H, t, J = 7.3 Hz, ArH) and 7.01 (2H, d, J = 7.3 Hz, ArH); GC (CDCl3) 14.07, 15.42, 14.44, 31.41, 32.51, 33.93, 34.91, 123.88, 129.70, 131.77, 132.63, 136.89, 139.15, 139.26 and 146.88; m/z 278 (M+) (Found: C, 90.75; H, 9.56. C21H26 (278.44) required C, 90.59; H, 9.41). Trans-tert-butylation of 8b with AlCl3±0H122 in benzene was carried out for 12 h under the same reaction conditions and the reaction mixture was treated as described above to afford 10 in 85% yield as a colourless prisms. AlCl3–MeNO2 Catalysed trans-tert-butylation of 9 in benzene: To a solution of 9 (230 mg, 0.68 mmol) in benzene (30 mL) was added a solution of AlCl3 (27.2 mg, 0.204 mmol) in MeNO2 (0.05 mL). After the reaction mixture had been stirred for 12 h at 50 °C, it was poured into ice-water and extracted with ether (30 mL u 2). The ether extract was dried (Na2SO4) and concentrated under reduced pressure to leave the residue. The residue was chromatographed on silica gel (Wako C-300, 200 g) (hexane as eluent) to give 10 (161 mg, 85%) as a colourless solid. Crystallographic data (8a): Crystal data for 8a: C24H32, M = 320.52, monoclinic, P121/n 1, a = 12.557(5), b = 8.833(3), c = 17.250(7) Å, V = 1814.4(13) Å3, E = 108.4873(16), Z = 4, Dc = 1.173 g cm-3, P (Mo-KD) = 3.068 mm-1, T = 296 K, colourless prisms; 20741 UHÀHFWLRQV PHDVXUHG RQ D 5LJDNX 6DWXUQ &&' GLIIUDFWRPHWHU RI which 4021 were independent, data corrected for absorption on the basis of symmetry equivalent and repeated data (min and max transmission factors: 0.896 0.997) and Lp effects, Rint = 0.048, structure solved by direct methods (Sir2002), F2 UH¿QHPHQW R1 = 0.1036 for 3757 data with F2> 2V(F2), wR2 = 0.2836 for all data, 218 parameters. Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication numbers CCDC 711541. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: 144-1223-336033 or e-mail: [email protected]].

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Received 4 December 2008; accepted 2 February 2009 Paper 08/0316 doi: 10.3184/030823409X430185 Published online: 29 April 2009 References 1 T. Shimizu, R. Ueno, M. Ziewandy and T. Yamato, J. Chem. Research, 2009, 60. 2 S.A. Sherrod and V. Boekelheide, J. Am. Chem. Soc., 1968, 90, 6887. 3 S.A. Sherrod and R.L. da Costa, Tetrahedron Lett., 1973, 2083. 4 S.A. Sherrod, R.L. da Costa, R.A. Barnes and V. Boekelheide, J. Am. Chem. Soc., 1974, 96, 1565. 5 F. Vögtle, Chem. Ber., 1969, 102, 3077.   '7+HIHO¿QJHUDQG'-&UDPJ. Am. Chem. Soc., 1970, 92, 1073.   '7+HIHO¿QJHUDQG'-&UDPJ. Am. Chem. Soc., 1971, 93, 4767. 8 A. Renault, C. Cohen-Addad, J. Lajzerowicz-Bonneteau, J.P. Dutasta and M.J. Cris, Acta Crystallogr., Sect. B, 1987, 43, 480. 9 T. Yamato, J. Matsumoto, K. Tokuhisa, K. Tsuji, K. Suehiro and M. Tashiro, J. Chem. Soc., Perkin Trans. 1, 1992, 2675. 10 T. Yamato, K. Tokuhisa and H. Tsuzuki, Can. J. Chem., 2000, 78, 238. 11 T. Yamato, K. Noda and H. Tsuzuki, New. J. Chem., 2001, 25, 721. 12 M. Tashiro and T. Yamato, J. Org. Chem., 1981, 46, 1543. 13 M. Tashiro, K. Koya and T. Yamato, J. Am. Chem. Soc., 1982, 104, 3707. 14 M. Tashiro and T. Yamato, J. Org. Chem., 1985, 50, 2939. 15 T. Yamato, T. Arimura and M. Tashiro, J. Chem. Soc., Perkin Trans. I., 1987, 1. 16 M. Tashiro, A. Tsuge, T. Sawada, T. Makishima, S. Horie, T. Arimura, S. Mataka and T. Yamato, J. Org. Chem., 1990, 55, 2404. 17 T. Sato and T. Takemura, J. Chem. Soc., Perkin 2, 1976, 1195. 18 M. Tashiro and T. Yamato, J. Org. Chem., 1981, 46, 4556. 19 K.K. Ellis, B. Wilke, Y. Zhang and S.T. Diver, Org. Lett., 2000, 2, 3785. 20 K.K. Ellis-Holder, B.P. Peppers, A.Y. KJovalevsky and S.T. Diver, Org. Lett., 2006, 8, 32511. 21 A.W. Hanson, Acta Crystallogr., 1962, 15, 956. 22 K. Yasushi, Y. Noritake and K. Nobutani, Acta Crystallogr., 1977, B33, 759.  3 .HHKQ DQG 60 5RVHQ¿HOG HGV Cyclophanes, Academic Press: New York, 1983, vol. 1, chap. 6, p. 428. 24 F. Vögtle, Cyclophane-chemistry, Wiley, Chichester, 1993. 25 D.J. Cram, D.L. Helgeson, D. Lock and L.A. Singer, J. Am. Chem. Soc., 1966, 88, 1324.

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