for 20 min and crystallization from CH2Cl2–ether afforded
8aؒPF6Ϫ (215 mg, 81%) as dark blue powder, mp > 300 ЊC (from
CH3CN–ether) (Found: C, 61.9; H, 3.4; S, 10.4. Calc. for
C31H19S2ؒPF6: C, 62.0; H 3.2; S, 10.7%); νmax (KBr disk)/cmϪ1
1472, 1453, 1393, 1291, 1169, 839 and 558; λmax (MeCN)/nm
248 (log ε 4.61), 309 (4.63), 357 (4.47), 404 sh (4.21), 451 sh
(3.95), 594 sh (3.92) and 718 (4.54); m/z (FAB) 455 (Mϩ Ϫ PF6).
adding an appropriate buffer solution (5 ml) and MeCN. The
pH of each sample was made on a Horiba pH meter F-13
calibrated with standard buffers before use. The observed
absorbance at the specific absorption maxima in visible region
of the cations 7a,b, 8a,b and 9a,b were plotted against the pH,
giving classical titration curves whose midpoints were taken as
the pKRϩ values.
Bis[6-isopropyl-9-(azuleno[1,2-b]thienyl)]phenylmethylium
hexafluorophosphate (8bؒPF6 )
؊
Acknowledgements
Ϫ
The same procedure used for the preparation of 7aؒPF6 was
adopted. The reaction of 18b (109 mg, 0.202 mmol) with DDQ
(55 mg, 0.24 mmol) in CH2Cl2 (18 ml) at room temperature for
25 min and crystallization from CH2Cl2–ether afforded 8bؒPF6
The present work was supported by a Grant-in-Aid for
Scientific Research (No. 14540486 to S. I.) from the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
Ϫ
(87 mg, 63%) as dark green plates, mp 135.2–136.0 ЊC (from
CH2Cl2–ether) (Found: C, 65.4; H, 4.5; S, 9.4. Calc. for
C37H31S2ؒPF6: C, 64.9; H 4.6; S, 9.4%); νmax (KBr disk)/cmϪ1
1474, 1393, 1281, 1242, 837 and 558; λmax (MeCN)/nm 250 (log
ε 4.54), 261 sh (4.50), 312 (4.65), 359 (4.48), 404 sh (4.20), 573 sh
(3.83) and 721 (4.46); m/z (FAB) 539 (Mϩ Ϫ PF6).
References and notes
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N. Morita and T. Asao, Bull. Chem. Soc. Jpn., 1996, 69, 3225–3237;
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J. Org. Chem., 1999, 64, 5815–5821.
[9-(Azuleno[1,2-b]thienyl)]diphenylmethylium hexafluoro-
phosphate (9aؒPF6؊)
Ϫ
The same procedure used for the preparation of 7aؒPF6 was
adopted. The reaction of 20a (105 mg, 0.300 mmol) with DDQ
(81 mg, 0.36 mmol) in CH2Cl2 (30 ml) at room temperature for
10 min and crysatllization from CH2Cl2–ether afforded 9aؒPF6
(122 mg, 82%) as red powder, mp 188.8–190.0 ЊC decomp. (from
CH3CN–ether) (Found: C, 60.8; H, 3.8; S, 6.7. Calc. for
C25H17SؒPF6: C, 60.7; H 3.5; S, 6.5%); νmax (KBr disk)/cmϪ1
1547, 1447, 839 and 558; λmax (MeCN)/nm 230 (log ε 4.46), 269
sh (4.25), 284 (4.29), 327 (4.23), 382 (4.14), 441 sh (4.15) and
486 (4.26); m/z (FAB) 349 (Mϩ Ϫ PF6).
Ϫ
[6-Isopropyl-9-(azuleno[1,2-b]thienyl)]diphenylmethylium hexa-
؊
fluorophosphate (9bؒPF6 )
Ϫ
The same procedure used for the preparation of 7aؒPF6 was
adopted. The reaction of 20b (73 mg, 0.19 mmol) with DDQ
(130 mg, 0.573 mmol) in CH2Cl2 (8 ml) at room temperature for
20 min and crystallization from CH3CN–ether afforded
Ϫ
9bؒPF6 (95 mg, 95%) as red powder, mp 139.0–140.0 ЊC
decomp. (from CH2Cl2–ether) (Found: C, 62.8; H, 4.1; S, 5.9.
Calc. for C28H23SؒPF6: C, 62.7; H 4.3; S, 5.8%); νmax (KBr disk)/
cmϪ1 1439, 1325, 1175, 837 and 558; λmax (MeCN)/nm 233 (log ε
4.40), 272 sh (4.31), 281 (4.33), 326 (4.17), 387 (4.14) and 481
(4.17); m/z (FAB) 391 (Mϩ Ϫ PF6).
10 K. Yamamura, N. Kusuhara, Y. Houda, M. Sasabe, H. Takagi and
M. Hashimoto, Tetrahedron Lett., 1999, 40, 6609–6611.
11 T. Sato, Bull. Chem. Research Inst. Non-Aqueous Solutions, Tohoku
Univ., 1959, 8, 47–62 (Chem. Abs., 1960, 10509).
12 The average chemical shift for the cations 7a,b was calculated by
simply taking an average of the entire chemical shift values in the
seven-membered ring without the distinction of the conformational
isomers 7A and 7B.
The pKR؉ value
Ϫ
Sample solutions of the hexafluorophosphates 7a,bؒPF6 and
8bؒPF6Ϫ were prepared by dissolving 1–2 mg of the hexafluoro-
phosphates in MeCN and a glycine (0.1 M) solution (50 ml) and
made up to 100 ml by further adding MeCN; the sample solu-
tion with lower acidity was made by further alkalification with
20% aqueous NaOH. For the preparation of a sample solution
13 PM3 semi-emprical MO calculations were performed by MOPAC
version 6 on a Tektronix CAChe WorkSystem.
Ϫ
Ϫ
of the hexafluorophosphates 8aؒPF6 and 9a,bؒPF6 , buffer
solutions of slightly different acidities were prepared by mixing
CH3COONa (1 M) and HCl (1 M) for pH 1.0–3.0, CH3COONa
(0.1 M) and CH3COOH (0.1 M) for pH 3.2–5.0, KH2PO4
(0.1 M) and Na2B4O7 (0.05 M) for pH 6.0–9.0, Na2B4O7 (0.05
M) and Na2CO3 (0.05 M) for pH 10.0, and Na2B4O7 (0.05 M)
and NaOH (0.1 M) for pH 11.0–11.4, in various portions. Each
1 ml portion of the stock solution, prepared by dissolving
2–3 mg of the hexafluorophosphates 8aؒPF6Ϫ and 9a,bؒPF6Ϫ in
MeCN (20 ml), was pipetted out and made up to 10 ml by
14 (a) T. Asao and S. Ito, J. Synth. Org. Chem., Jpn., 1996, 54, 2–14;
(b) S.-I. Takekuma, M. Tanizawa, M. Sasaki, T. Matsumoto
and H. Takekuma, Tetrahedron Lett., 2002, 43, 2073–2078;
(c) M. Sasaki, M. Nakamura, G. Hannita, H. Takekuma,
T. Minematsu, M. Yoshihara and S.-I. Takekuma, Tetrahedron Lett.,
2003, 44, 275–279; (d ) M. Sasaki, M. Nakamura, T. Uriu,
H. Takekuma, T. Minematsu, M. Yoshihara and S.-I. Takekuma,
Tetrahedron, 2003, 59, 505–516.
15 (a) R. C. Kerber and H. M. Hsu, J. Am. Chem. Soc., 1973, 95, 3239–
3245; (b) K. Komatsu, K. Masumoto, Y. Waki and K. Okamoto,
Bull. Chem. Soc. Jpn., 1982, 55, 2470–2479.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 2 5 7 2 – 2 5 8 0
2580